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Posted by: horizontally-opposed Jan 26 2021, 12:21 PM

I've been reviewing past discussions on these (links below) off and on, having test fit a 215/60R15 Pirelli P6000 on a 911R wheel into both rear fenders of my narrow-body 914. It seems doable, but it's going to take some massaging on the outer fender, custom spacers, and—maybe—narrowed trailing arms. Which got me to thinking about the current state of the 914 trailing arm, which is the same it's been since 1970.

Basically, those heavy, non-adjustable steel trailing arms are one of the very few things on the 914 that hasn't been addressed or evolved by the aftermarket.

I'm running PMB-rebuilt trailing arms with PMB-rebuilt calipers, and can redo them again with reinforcements and/or some reshaping, but I wonder how hard would it be to do blade-type trailing arms of similar strength with less weight and/or more adjustment. Could a 911 spring plate, or a triangulated or otherwise reinforced version of it, be adapted? Looking at the basic design of the 914 arm, it doesn't look all that complicated, but I'm no engineer.

EDIT: Possible use of a machined 986 wheel carrier, an aluminum casting by Brembo that incorporates the 986 e-brake and 986 four-piston caliper mounts, comes up later—a very interesting idea from @http://www.914world.com/bbs2/index.php?showuser=431, particularly as the castings are available for $100-200ea used or new from Porsche. Bolting that carrier to a new steel trailing arm with a lower damper mount seems viable to me, but here to learn.

The custom work to narrow factory 914 trailing arms looks extensive, but has been done by both @http://www.914world.com/bbs2/index.php?showuser=137 and @http://www.914world.com/bbs2/index.php?showuser=2744 as well as, it looks like, Rich Johnson. I could see doing it in the process of moving to 911 e-brakes and 986 2.5 brakes, maybe, but I wonder if a group buy might attract a 914 vendor we all want to support?

Relevant threads:

http://www.914world.com/bbs2/index.php?showtopic=101992&st=0&p=1247827&#entry1247827

http://www.914world.com/bbs2/index.php?showtopic=618&hl=trailing&st=0

http://www.914world.com/bbs2/index.php?showtopic=238144&st=0

http://www.914world.com/bbs2/index.php?showtopic=234391&st=0

Posted by: Mark Henry Jan 26 2021, 12:32 PM

I'll look through the links later, interesting.

One issue is the 215/60R15 tires, your choice beyond sucks, best tire you can do is a very short list of all season and winter tires.

Now do this and fit in 17x7" rims and you might have a winner.

Posted by: horizontally-opposed Jan 26 2021, 12:32 PM

Test fit of 215/60R15 in stock rear fenders:


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Posted by: horizontally-opposed Jan 26 2021, 12:37 PM

And on a 911R wheel with stacked washers to optimize spacing.

The wheel/tire fit into both fenders so that the car could be safely lowered, but the fenders would need a bit of rolling/pull before the wheels were spaced further out. It's been done with regular 15x7 Fuchs and Cookie Cutters, but the 911R wheel will provide better offset.


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Posted by: horizontally-opposed Jan 26 2021, 12:40 PM

Interference!


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Posted by: eeyore Jan 26 2021, 04:21 PM

If you want to go off into the weeds for ideas, look at the rear suspension bits for the Audi/VW MQB platform (e.g. Tiguan 4motion, Q3 or Q5?)

They have a blade type rear suspension with transverse links for camber and toe control.

Posted by: gms Jan 26 2021, 04:34 PM

I have always thought it would be great if someone made trailing arms out of cast aluminum like the later 911s

Posted by: Chris914n6 Jan 26 2021, 04:41 PM

I have a 225/50-16 stuffed in the rear. I ran out of room between the sheet metal way before the arm could be an issue.

2nd thing... why would I ever want an oversized 215/60-15 with huge sidewall bulge?

Posted by: horizontally-opposed Jan 26 2021, 04:45 PM

This. Or carbon fiber if it makes sense, at this point.



On factory 16x7s, right? I have seen it done a few times. I'm more interested in getting the tire inboard on a 911R-style wheel, as I want to stay with 15s and the "narrow body" look.

185/70R15 or 195/65R15 front and 215/60R15 are the correct spec with the right overall diameter for a lot of Porsches—from the 1973 911 Carrera RS through Carrera 3.2s and 944s of the late 1980s. Good setup, several performance tires available, and period correct looks. There's a lot to like about factory tire sizes—and now there are some good wheel choices as well, ready to mount for similar or less money than "normal" Fuchs that need to be restored and a lot less than previously unobtanium 911R wheels.

https://tremotorsports.com/exterior/fuch-style-deep-6-7-wheels

Posted by: SirAndy Jan 26 2021, 04:48 PM

From the looks of it, even if you did use slimmer trailing arms, you don't have *any* space left for the tire to move as the suspension loads.

Every little bump in the road will make the inside of the tire rub. What you show in the pic below is not nearly enough clearance to deal with camber changes as the suspension moves.

Posted by: horizontally-opposed Jan 26 2021, 04:54 PM

Precisely my point above re: dynamic clearance. I know a 215 or 225 can be snuck into the fender, though. Plenty of people have done it.

Tire is going to have to come out, which means more spacer. That may alleviate the need for a relocated brake line or a narrowed trailing arm somewhat, but I am not sure that it would help enough given 914timo's experiences.

Posted by: 914forme Jan 26 2021, 05:34 PM

I ran 225 on 15s never 16s, spacers where used for inner clearance. Fenders ended up being mildly flared to do it.

LOL these where Hoosiers A7 so they tend to run a bit wider than the numbers on the sidewalls. Rule of thumb in NASA racing is the Hoosier run 20 over the number posted on the sidewall.

Would prefer to do a carbon fiber arms if redesigning an arm, but lets be real, if going to all that, change it from a trailing arm to something a bit better. Not going to say what the would be but for me I have had my dream setup for a long time.

Then I hit the easy button and bought a Boxster. Now I can run 285 out back, and 255s up front. Problems solved. All that is missing is an LSD and more power just like the 914, one of two of these items will be solved shortly. The other will be solved when the right car pops up on coparts

Posted by: mskala Jan 26 2021, 07:22 PM

I'm not sure of your goal, here. Is your desire wide tires? Or
60-series tires (balloons)? Or do you really just want 911R rims?
Or do you love fabricating stuff just to say you did it?

So my comments may or may not be helpful. On my -6, I can
run Hoosier A7 205/45/16 on a 7.5" rim. It does not have flares.
The fender lips were flattened and pulled on a bit, and I am
using about 2 degrees negative camber. They have rubbed the
paint off the inner fender over time. I needed to get the spacers
right, and I have them in 3mm increments.

Before I had hoosiers, I video taped my suspension with other
racy tires, and like Andy said, they move a lot under side loads.
If you have good paint you don't want to destroy, give yourself
1/2" on each side. The 914 is great if you have plastic bushings,
since you can disconnect the shock and move the arm up and
down as far as you want to check the static fit.

In my opinion, you will never be able to fit the tires you're showing
without fender work.

I don't understand what the trailing arm width has to do with
fitting tires, the stock ones will accept a wide wheel in the location
it needs to be.

Rather than fabricate arms for no reason, you can just get some
Fuchs and have them widened on the inside, and use appropriate
spacers. That has to be cheaper and easier than custom arms,
and probably nobody will will be able to tell.

Posted by: mepstein Jan 26 2021, 08:00 PM

Pete - I don't think you will get wider tires on the car without messing with your fenders in some fashion. In addition, the higher aspect ratio tires will always move more side to side and need more room to keep them off the fender. Ive seen a couple 914's and 911's burn through the paint on the fender from tires that "just fit".

Posted by: horizontally-opposed Jan 26 2021, 08:08 PM

^ Several people have narrowed the trailing arms. I've had 205/60s and 205/55s in my stock rear fenders over the years with no issue. Others have gone up to 225/50R16 or 225/50R15 in stock fenders "with a bit of work." That work has varied. There are a number of threads.

215/60s are hardly "balloons," as that's the factory aspect ratio/overall diameter for all 15-inch applications. I happen to love the bulging sidewall with 215/60—but it's a matter of taste as 50- or 45-series rubber looks incorrect on these old cars. Again, a matter of taste/preference.

Agree on dynamic clearance, and well aware of that phenomenon, but feel that can be dealt with on the fender side and a wheel spacer. Trailing arm/brake line clearance was a bigger problem when I did the test fit, so it would be good to address it.

Trailing arm question came after reviewing threads of others' experiences in sneaking more rubber into a narrow body car. Many of them narrowed the trailing arms, particularly with wheels that tuck the tire inward with the 911R offset (my preference), which I believe is preferable as an offset to a standard 15x7 Fuchs—both technically and visually.

Finally, trailing arm question is prompted by the idea of paying for a second round of work on my trailing arms. By the time you narrow a pair, adapt 911 e-brakes, add new bearings, etc, one begins to wonder if you want the same old boat anchor—and if you're alone. Curious if Dave Darling remembers who built/offered/canceled the blade type arms with camber/toe adjustment at the rear of the arms. Unsprung weight is always nice to get rid of, too—and I know several people building 914s that might be able to justify a better option for the rear arms. Perhaps the economics/demand is different now than it was then—but the hours involved in reworking old trailing arms may help offset the cost of something better.

The right design should have merit regardless of what wheels are used. If it provides more tire clearance on the inside, well, that's a boon.

Posted by: horizontally-opposed Jan 26 2021, 08:10 PM

^ Totally agree. This project, if it happens, will require a mix of things to sneak them in. But it's been done before.

Posted by: Chris914n6 Jan 26 2021, 09:37 PM

Stock wheels & tires, for a Boxster
With spacers I think I ended up at Fuchs 911 offset and a bit of camber and rolled the fender.

I think I test fit a 215/60 on a 7x15 cookie from the 944 set I bought. Billowing sidewalls. Might as well call them pillow tires for a sleepy drive

Found it. Silver cookie is a 6". I recall the 7" rubbed or was otherwise not worth using for donuts.











For comparison wide 205/55 on a 7x16 911 Fuch spec. Basically the same as my Boxsters.

Posted by: horizontally-opposed Jan 26 2021, 10:21 PM

Silver cookie setup looks good to me.

As for pillows…  yeah maybe for all-seasons. But 185/70 front & 215/60R15 rear was standard for a 1973 Carrera RS while 195/65 front & 215/60R15 rear is standard for a 911 SC and Carrera 3.2. So that's a pretty attractive "maximum" setup for a narrow-body 914 with 200-250 hp—and Avon CR6ZZ are available in those sizes and were available from Roger Kraus Racing in three compounds last time I bought a set of 185/70s. Pirelli P6000 and CN36 are available in those sizes, too—and the revisions might accept 225/50R15 rears as well, which opens the door to Toyo RA1s and other interesting options if the car ever sees a track again.

It's going to take some work, but others have done it—on both narrow 914s as well as narrow early 911s—and whatever the work…it's a lot less work than GT flares and painting both sides of the car. Figure it can be pulled for now, and perhaps redone to a higher standard with the next paint job. Need to put some more miles and rock chips on this one first.




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Posted by: Chris914n6 Jan 27 2021, 01:57 AM

I have a set of 225/50-15 on Fuchs I've been wanting to trial fit. Will be at least a week before it stops being cold and wet.

Also, I can spin my 225s in 2nd with 200hp, so 215 isn't going to change anything from 205.

So really, that's alot of work for 1/2" just because Porsche did it on the bigger 911 & 944 in the 80s.

Posted by: mskala Jan 27 2021, 06:53 AM

I wasn't trying to judge what you're doing, whatever you want it's great.

Note one other thing; maybe you already know, but a wider wheel makes
the section width of the tire wider also. The 911R 7" rim is 49mm offset
and Fuchs 6" rim is 36mm offset, so the outside of the rim will be in
the same plane when mounted. So there is no benefit to using 911R rims
(if the tire will mount safely, which 225 or less will.)

Posted by: Racer Jan 27 2021, 07:02 AM

its my recollection that the Maxlite 911R wheel is NOT an exact 911R replica. Maxlite is 47mm offset while the original 911R is 49mm offset.. and in this case, 2mm will matter!

We had a 74 911S (stock narrow rear fenders) and ran 911R wheels with 225/50-15 yokohama A008 (1980s here for reference). Despite fender lip rolling (like yours) previously on our 914/6 (to fit a 205/70-14 in period tire combo), that 911R combo just wouldn't fit on our /6 or on my /4. Both cars would require a slight pull of the fenders to work (but less pull than a 7x15 et23 wheel). fwiw, on our /6, the 205/70-14 was an extremely close fit, such that a 195/70 became the default tire in the 1970s on that car.

You also need to take into account tire flex / expansion and suspension movement etc under use.. and the harder the use, the greater the movements.

Another question, even if the trailing arm was made thinner, what is the relationship (plane) between the arm and the inner fender well? Does the arm protrude past the inner fender well or sit flush? ie, even if you thin the arm, will the tall tire still hit the inner fender?

Posted by: Andyrew Jan 27 2021, 08:19 AM

My issue has always been rubbing the top of the chassis sheet metal. I've done it many times and have the half moon scars to prove it


Not once have I hit the trailing arm, and if the brake line got in the way then it was relocated.

If we didnt have increased camber as the tire went up then the trailing arm might be more of an issue.....

Also I have a fairly well sprung ride (225/275) so I dont have excess travel like a softer car.



I think your looking at the wrong issue here Pete. With the stock chassis 914 owners need to go outwards for larger tires. Not inwards.

(That being said... I have always wanted to build a tube chassis rear that can put a significant amount of tire more inward....)

Posted by: mepstein Jan 27 2021, 09:04 AM

Pete - Just buy this.


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Posted by: 914forme Jan 27 2021, 07:11 PM

The original Sheridan car had a custom set of rear arms with all the toe and camber settings out on the end of the arm.

Can be seen in the ultimate 914 racer Articles in European car circa 2013

Posted by: horizontally-opposed Jan 27 2021, 07:51 PM

Ah, Roger's car. I wonder if that's the one Dave Darling was thinking about?

Looks like they're pretty trick—as is so much of that car—but that they push the ultra-wide wheels even further out, as one can with the Ultimate 914 bodywork.




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Posted by: horizontally-opposed Jan 27 2021, 07:57 PM

Thinking more down this road…though 914 unibody is obviously very different.






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Posted by: sixnotfour Jan 28 2021, 06:33 AM

Half way there..


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Posted by: rick 918-S Jan 28 2021, 07:39 AM

I totally get the look. 15's with vintage looking tires are so period 914. It really sucks that the tire selection is so limited. I really liked the Yokohama's mounted on my 15X8's with 225/60's and 215/60's vintage cool. I ended up going to 16X8 and 16X9's running 275/50's and 225/50's Yokohama tires until they discontinued the 275's I am down to one tire selection and that will eventually evaporate too.

Question: I don't have a car here at the new house I can examine. Is the trailing arm the first obstacle inboard or is the body sheet metal the first point of contact?

The trailing arms can be modified pretty easily really without going to a flat plate type arm if there is any benefit.

Posted by: horizontally-opposed Jan 28 2021, 09:48 AM

Holy moly…

Posted by: horizontally-opposed Jan 28 2021, 09:54 AM

Your car looked fantastic on the 15s—I hope you kept them? I am hearing more and more good things about the Radial T/A, which appears to be available in 215/60 and 225/60. I wrote them off as Trans-Am tires but some Porsche guys are running them out here and say they feel good. They were cheap for a long time, then went up considerably (still much cheaper than Avons or a lot of other tires). My guess is that Michelin, which owns BFG, may have updated the technology behind them or at least the compounds. May be worth a shot, with black letters out?

And yes 16 choices are thin on the ground these days but better than they were a couple of years ago. Period P7s and a good Yokohama are out now, both of which would look great on a 914 with M471 flares, though they're 225/50 and 245/45. The fact that 15s went to near zero choices, sending many to 16s, suggests maybe the 16s will come around again too. I know people who buy and bag tires for old cars when they come available, as they're loathe to settle for all-seasons or worse, no tires at all—a big part of why I'm liking factory tire sizes. They not only look right, they're likely to be available in at least 1-2 sizes.



First point of contact is brake line & trailing arm—there's room at the inner fender, to my surprise with a 215, though not enough for the tire to move around under load. So pulling the outer fender and adding more spacer will help the inner fender more than the brake line & arm. Right solution probably needs to address both.

Sounds like I might be shopping for a pair of good trailing arms…

Posted by: Montreal914 Jan 28 2021, 10:25 AM

A few years back, planning on my 5 lugs upgrade, I had a nice set of 15 x 6 Fuchs. After reading that the tire selection is greater with the 16", I sold them and got a set of 16 x 6.

I am currently preparing my narrow body car for paint and will eventually reassemble it with the 5 lugs.

I am puzzled as to what summer tire selection there actually is in the 16" . It feels like the selection is greater in the 15", or am I missing something...

Being in SoCal, I am looking at summer tires, but don't want too much of a modern look. I understand that by switching to 16, I walked away from the proper era look

Sorry to jump in the OP's thread, but I know Pete is thoroughly investigating the tire file... I read one of your post talking about the Michelin Pilot Sport AS3 205/55/16. I am not sure if this model is still available though...

Interesting topic!

Posted by: horizontally-opposed Jan 28 2021, 10:59 AM

16x6 allows for some GREAT tires—from (at last check) the Pilot Sport AS3, which has a simple sidewall and an "old enough" looking tread pattern and more than enough performance and feel for me on the street, to some pretty serious R-compound tires for autocross and track use. Last I checked, not only Toyo RA1 but also Michelin Cups and some others.

The good news with 205/55R16 is it was original fit for Porsches on 16-inch alloy wheels from 1975~ through 2004 (last of the 986s on 16s) as well as a ton of other performance cars built in big numbers, such as the Subaru WRX. The bad news is sneaking them into the rear fenders. I had no problems with 205/60R15 other than a bit of rubbing on the inside, so you might get them in. Some 914s seem to have less clearance than others.

You may also have a bit of interference up front depending on where your wheels sit in the fenders (I use spacers up there, and 185/70s can occasionally just barely catch my LE-style spoiler with the right amount of steering lock and suspension compression, such as on the way into a certain kind of driveway…though it's ultra rare and I've seen zero damage). But if you sort them, as many have, 205/55R16 is a wonderful size for a narrow body 914 and probably the ultimate performance setup without resorting to much in the way of trickery.

Looks like the AS3s are available in H-rated or V-rated for $135-140ea, but may be on closeout? But whatever, I doubt availability or selection will be a problem with 205/55R16. 225/50R16 may be a bit more of an issue, and 245/45R16 has already been an issue (being down to track tires or Fuzion, take your pick) but there are some very good 245/45 options out there again.

Posted by: Montreal914 Jan 28 2021, 01:54 PM

Thank you for this very valuable information
I will look for some AS3 I do have an LE replica valence, and also have a set of thin spacers (6-7mm?) off of a 68 911 that I might use in the front to fill up. I will definitely keep in mind all of the clearance issues you have pointed out. I hope the rear wont be an issue. Didn't think it would be... You are now making me wonder if I should try the rear fit before having the car painted, but that would mean installing the new 5 lugs trailing arms and... Many things to think about, Thank you!!!

Posted by: horizontally-opposed Jan 28 2021, 02:20 PM

^ You are welcome, but @http://www.914world.com/bbs2/index.php?showuser=2744 is probably our resident king of sneaking 205/55R16s into stock or stock-ish rear fenders.

I just wanted to get a conversation about rethinking the 914's trailing arms going.

After some more thought, I wonder if I can't rope @http://www.914world.com/bbs2/index.php?showuser=19709 in, as some of the thinking stems back to the dreamy "GT" build we commissioned him to render for 000 (below) and might even tie into something else he's working on.

If a North American wheel supplier can create custom billet 20x12-inch wheels that exactly match Porsche AG concept car wheels for $1250~/wheel, I have to suspect two pieces of billet aluminum to accept stock, poly, or needle bearings up front and a 911 e-brake, wheel bearing, and a caliper at the back connected by a "blade" or two of carbon fiber might not be so crazy? It would be interesting to compare prices for the above against making jigs to narrow 50yo steel arms, adapting 911 e-brakes, repainting, and rebushing a set of stock trailing arms—which would still be boat anchors. Lightweight arms might save 20-30~ pounds in unsprung weight. Pair that with a lightweight battery, and it could add up to half~ the weight gain of a six conversion in roughly the same part of the car. Not gonna be cheap, but look what folks spend on bodywork, paint, wheels, lightweighting (!), etc.


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Posted by: mepstein Jan 28 2021, 02:45 PM

Pete - Have you weighed a 914 trailing arm. They look heavy but really not that bad. I don't have one in front of me but I'm guessing a bare one at 12-15lbs.

Posted by: horizontally-opposed Jan 28 2021, 03:28 PM

I've handled three pairs of them over the years, with and without other parts on them, and they seemed like a heavy, strong, and inexpensive part for a mass-produced car.

Kinda like early 911/912/911 steel crossmembers, before PAG moved to aluminum.

I'd be curious to know their weight without bearings, etc.—as that would be the relevant comparison. In the old days, I could head down to EASY and very likely weigh one. Those days are gone, sadly.

Posted by: ClayPerrine Jan 28 2021, 03:35 PM

Just put this under the back of your 914. Better suspension design, already has a parking brake and big vented rotors.

Posted by: horizontally-opposed Jan 28 2021, 03:44 PM

^ Ha.

Guessing this requires cutting the 914's unibody up, isn't compatible with 914's track width, wouldn't fit under standard 914 fenders, and would ultimately be heavier and more expensive than custom trailing arms let alone a small run of lightweight arms…

Posted by: mepstein Jan 28 2021, 04:23 PM

I'll do it tomorrow if nobody beats me to it.

Posted by: rick 918-S Jan 28 2021, 04:30 PM

If I had my new shop set up I would build a gig and narrow a couple. One of you guys should take this on for Pete. Couldn't take but a couple days of messing around to make a couple.

Posted by: Eric_Shea Jan 28 2021, 04:35 PM

We could play with it if you want...

Posted by: mskala Jan 28 2021, 05:01 PM

7.5"x16 ET38 wheels, minimal spacers different on each side. Normal trailing arms.
Hoosier 205/45/16 which of course runs wider than numbers would suggest.
Does not hit the brake line or arm. Fenders were yanked a bit and folded. Inner
wheel well rubs first, before you would rub brake line or trailing arm.

Posted by: horizontally-opposed Jan 28 2021, 06:15 PM

Thanks, Rick—but I am actually interested in something for more than me.

Our 914s have always lived in the shadow of the 911 when it comes to suspension upgrades, being "lucky" to benefit from parts developed for the front of the 911 and even luckier if a matching rear damper/spring was available. I get the idea that there wasn't enough market to justify the developments we've seen for 911s in years past, especially when 914s were $5000-30,000 cars, but I have to wonder if there isn't now?

How many people have made jigs to narrow two trailing arms (I've found several independent jobs in my research) and/or slice off the wheel carrier to weld up a 911 e-brake to gain access to better/lighter calipers? And you're still dealing with a 50yo arm that might need to be repainted, etc. And maybe reinforced, too—though there are two schools on that. How much does all that labor add up to?

Might be cool nice to see something developed that addresses all that, takes any of the three available bushing types up front, accepts a 911 e-brake, can accept different calipers via adapters (914, 930, 986), and maybe offers some adjustment with 2-3 mounting points for the rear damper. Won't be cheap, but people are spending real money on 914s these days. I know of someone who might be willing to fund such a thing if it's done to a high level—and that would leave a cool product on the market. Or maybe we can figure out a group buy. I've been cooking through another idea that might drop serious weight off the back of the 914, and might not be insane in lieu of what some are spending or will eventually spend in this area of the car. I know an F1 contractor who might be cajoled into helping with the billet aluminum (or?) sections, but we also have some very smart cats here.

Yes, I'm definitely thinking out loud—and taking some hits for it—but that's all good.






Thanks for this, and very cool to see. I've seen people sneak 16x7 Fuchs in (both 951 and maybe 911 too?), but not these—as they appear to have a bit of lip on them. 205/45R16 definitely seems to help, too. @http://www.914world.com/bbs2/index.php?showuser=2744 is running custom 16x7.5 Fuchs also, I think, but they're flat-faced with the added width on the back iirc. Like a 16-inch 911R wheel.

As you note, actual tire widths ≠ tire sizes. When I ran 205/60R15 A-008Rs, I had the same point of interference as you and no interference at the brake line/trailing arm. I went on to drop down to 205/55R15 BFGs and, later, Yokos, and had no issues. 185/70 and 195/65 have all been fine, but no surprise there. Test fit with the 215/60R15 Pirelli P6000 shows brake line clearance is a bigger problem than inner fender clearance—so pulling the fender and spacing the wheel further out will help the inner fender more than the brake line, and I'd love to minimize that fender pull…




Was hoping you might chime in, as one of very few logical vendors for trick 914 trailing arms.

Would be great to compare notes and do some thinking…

Posted by: mskala Jan 28 2021, 06:49 PM

Slight error with the pic, it was taken earlier with Kumho V710 215/40/16, which I
measured as 8.5" section width. Hoosier was wider than this.

Posted by: mepstein Jan 28 2021, 07:33 PM

185/70 front & 215/60R15 rear was standard for a 1973 Carrera RS

So one of Porsche's most iconic cars made due with relatively narrow rubber and a 914 could be said to be lighter and better balanced.

Is it just about getting the wider tire on the car. Better handling. Both?

One thing that was suggested to me to improve the ride and handling on our cars was better custom valved shocks. The most common shock upgrade to Bilsteins just uses a 30+ year old design.

We all just tend to throw a lot of "upgraded part" on our cars without really testing how they work together, sometimes assuming a stiffer ride will be a high performance ride.

Posted by: horizontally-opposed Jan 28 2021, 11:23 PM

We're on the same wavelength, and agree with much of the above—but would go further, and less far.

I've been testing factory and aftermarket Porsches on road and track since 1997. Long ago lost count of how many cars, track days, and road tests. Along the way, the cars that hit the sweet spot and were "soul connected" were the ones that stood out. They were often less is more, such as a 986 2.5 that was just plain more fun to drive than a 993 Turbo. Or the 987.2 Boxster Spyder, which was far more than the sum of its parts—and probably quicker over the road in the hands of more drivers than a contemporary GT3. And, dare I say it, more fun despite a merely wonderful engine instead of that insane Mezger.

There are a lot of other examples, but the 914 stands tall in this regard—and that goes for virtually any good 914.

The standouts from the Porsche aftermarket are even fewer and further between. Most go for more more more, and the experience isn't any better. And, I'd argue, the driver often ends up less confident, extracts less out of the car, and has less fun. Which is perhaps what you're getting at. I can probably count on 2-3 hands the number of truly brilliant aftermarket Porsches I've tried—they've been rare, and sometimes come from unexpected shops or individuals. One line usually tied them together: Those who carried out the mods were methodical, planned their ideas out carefully, and saw everything as a system. Again, what I think you're getting at.

When it comes to our 914s, a lot of people go for big engines, big brakes, and 16- or 17-inch rubber with 205-225 (or larger…) front tires and 225-265 (or larger…) rear tires. And some 914 hot rods do benefit from that despite relatively modest weight gains vs much less modest power gains. Others end up fast but distinctly un-fun or even scary to drive.

In terms of power, my 914 is making a modest 169 hp at the wheels, so maybe 190-200 hp at the flywheel (insert favorite "conversion/guestimation" here). Target achieved. The 1973 RS 2.7 was rated at 210 hp, and wasn't all that much heavier unless it was a full-boat RST. (One thing to remember re: 914 tire sizes: Wider road/consumer tires weren't widely available on Porsches before the RS 2.7, and were pretty rare in general. Up to 1973, a 185/70R15 was a wider performance tire, and something of a gold standard. Then the 215/60 arrived—and Porsche staggered the tire sizes on a lot of their cars, including even the most modest 2.5-liter early Boxsters.) Porsche used that same 185/215 or 195/215 wheel/tire package on 911s from the 260-hp early 930 through to the 230~ hp 1988 911—in other words, a wide variety of 911s with 180-260 hp and weights both below and above the 914. 16s with wider tires were available as an option or standard on some models (Turbo 3.3, SC, Carrera, SC/RS, Turbo Look, 1989 Carrera, etc). I'd say the 185/215 and later 195/215 has breadth, and we know that tire package met Weissach's performance standards. And the right tires of today in those sizes are better than tires of the same size back then. Much better.

My humble narrow-body 914 drove really well with 185-205 tires at all four corners when it had 80hp. I didn't need the 205s due to power, to be sure, but the chassis sure could put 205s to good use at high and low speeds. Perhaps more importantly, I just liked the car that way.

Fwiw, I was talked into Bilstein HDs by a number of people I respect during my last suspension rebuild. About the only thing we got right was sticking with rubber suspension bushings and the same spring rates. I vastly preferred my previous Koni reds to the HDs, and see no reason to reinvent the 914's torsion bar/coil-over concept or move to exotic and/or remote-reservoir dampers. I might convert my Koni reds to double adjustable, but I might not. Zero desire to go to higher spring rate up front, and will likely keep my fairly soft rear springs. Might go up 20-40lb. We'll see. There are other upgrades that are pretty interesting—such as Tangerine's strut top mount for lowered cars (been eyeing that one), raised spindles (should have done that last time), better bump-steer solutions, etc. Little stuff that can make a big difference. There is some big stuff out there, too, such as Elephant or ERP's A-arm replacements, but I am not sure these are right for a street car—especially at the front end.

On the other hand, trailing arms in modern materials and lighter brakes might offer a chance at serious weight loss (total, unsprung, and rotational). Steel trailing arms were cheap and strong. Heavy, too. Steel brake calipers and one-piece rear rotors were, as well. Better rear arms, alloy calipers, and maybe even two-piece rear rotors—if the right disc can be sourced and the e-brake can be figured out—might drop significant weight. No, it won't be cheap, but I suspect an Avon 215/60R15 on a 911R replica wheel on a lightweight arm with a lighter brake setup—along with a well thought-out front end—might end up less expensive than adding M471 or custom flares, the usual suspension/brake upgrades, and repainting the car. And for those of us who like the narrow-body look…

Posted by: Chris914n6 Jan 29 2021, 02:16 AM

~21.5 lbs as seen. Scale might not be 100% accurate.

Posted by: mepstein Jan 29 2021, 07:40 AM

So without the hub, bearing, bracket and shaft, fifteen-ish, maybe?

Posted by: horizontally-opposed Jan 29 2021, 10:02 AM

Thanks Chris!

A little lighter than I expected, but they certainly aren't light. There may be 30 to 50+ pounds in unsprung/rotational mass to be shed between the 914's steel arms, steel calipers, and one-piece steel rotors x2 while adding a number of technical upsides.

Question is how light they can be made, and for how much.

Next question is what the $ might look vs against narrowed/reinforced/e-braked/rebuilt arms. Or flares + paint. And then how many orders would it take for a vendor to step up? The concept is easy. The execution is well outside my ability, and likely prohibitive as a one-off, but it would be a great piece to have on the shelf while assembling parts for the next suspension redo…

Posted by: horizontally-opposed Jan 29 2021, 10:05 AM

Not much to be done with the wheel bearing, but the shaft and hub might be a place to apply better materials. Maybe also set up for four or five lug wheels.

Anyway, suspect your guess is within a pound or two.

Posted by: mepstein Jan 29 2021, 10:34 AM

Largest, easiest chunk of weight would be aluminum calipers. Eric did a run but I don't think there was ever a huge demand. I think it was the price that held people back.

I think part of the reason a stock 914 is such a joy to drive is the light, narrow tires. They may not provide ultimate traction but feel light and smooth and let the car "dance" over the road.

"I've been testing factory and aftermarket Porsches on road and track since 1997. Long ago lost count of how many cars, track days, and road tests. Along the way, the cars that hit the sweet spot and were "soul connected" were the ones that stood out. They were often less is more, such as a 986 2.5 that was just plain more fun to drive than a 993 Turbo. Or the 987.2 Boxster Spyder, which was far more than the sum of its parts—and probably quicker over the road in the hands of more drivers than a contemporary GT3. And, dare I say it, more fun despite a merely wonderful engine instead of that insane Mezger.

There are a lot of other examples, but the 914 stands tall in this regard—and that goes for virtually any good 914.

I get this. I've ridden and raced bicycles all my life. I ran a bike shop for 6 years so I rode hundreds of different bikes than just mine.
Most of the bikes I owned were top of the line, great bicycles and did there job well. Two of them were outstanding and I have not been able to duplicate the feel.

So maybe we should be aiming to hit that sweet spot with a 914. I've never driven a 911RS but it seems to get described in that way. So maybe we need to make a 914RS.
A magical riding car that can be duplicated.

Posted by: ClayPerrine Jan 29 2021, 10:38 AM

The factory trailing arms were designed with narrow tires and limited grip as the parameters. With 50 years of tire evolution, you can put enough sticky tires on a 914 that will make it exceed 1G lateral loads. The trailing arms were never designed for that kind of load, and are going to start failing from a combination of metal fatigue and age.

An aluminum trailing arm, similar to the 911 one, would be a great investment. If I were doing it, I would incorporate a mounting pad for a monoblock (Boxster) caliper, all the required provisions for the park brake (stop block, bellcrank, altered cable mount, etc..) and new fairly hard durometer rubber bushings.


But it is beyond a hobbyists ability to build a upgraded trailing arm like this.

Someone with some deep pockets would have to build and sell it.

Posted by: Superhawk996 Jan 29 2021, 11:18 AM

Well said! Doesn't exactly look profitable given a upper bound of ~100,000 vehicles and mabye 22,000 rabid fans (or whatever latest membership is here).

Now consider the number of those that would be willing to spend $$$ to make the "upgrade".

For me a good chunk of the 914 appeal is that it is what it is. Faster, more reliable, great handling cars are all around us in this day and age. Agree a 914 stands tall given its age but again, it is what it is.

Posted by: horizontally-opposed Jan 29 2021, 11:35 AM

This one would take a village to get done, but I think it's within the realm of possibility between our contacts and even some of the talent here. And I may have a "cost no object" buyer who might underwrite the most expensive pair (the first ones), as he was already thinking along same lines when I mentioned them. He's getting over Covid, and we were talking cars to keep him distracted. He's got a lot of other stuff, but loves his 914. And if a number of us signed on for a group buy…

Four billet aluminum ends won't be cheap, but they should be doable. Best way would be to incorporate choices such as which of three bushings/bearings up front and ears for 914, 930, or 986 calipers in the rear—leaving it up to the customer to move to 911 e-brake, RSR, or spot calipers. Or no e-brake.

Carbon or lightweight steel blades would probably be the "hard" part—after proper/safe design and FEA, that is.

Posted by: live free & drive Jan 29 2021, 03:31 PM

Maybe one could get an mechanical engineering grad student to undertake a project using some of the new generative design software and DMSL and print stainless or titanium trailing arms with the highest strength to weight ratios:

https://www.pinterest.jp/pin/541698661419803565/

Maybe not the cheapest, but you might get something pretty wonderous for $1400 per arm (give or take)

Autodesk has a new software out to design these type of organically perfected devices:

http://www.withinlab.com/case-studies/new_index18.php

Posted by: rgalla9146 Jan 29 2021, 03:39 PM

How's this ?
A single large monoball attached at current outer front trailing arm mount.
A rigid narrow cast or box type trailing arm that extends past the hub
and includes mounts for upper and lower un-equal length rear links.
The links extend inward toward the transmission and attach to a fabricated
hoop forward of the transmission mounts.
The loads are now through three mounts intead of two and are spread over
larger areas.
Full disclosure, I'm not an engineer nor could I plot the geometry.
Can't draw so well either.
Nonsense ?

Posted by: Chris914n6 Jan 29 2021, 04:51 PM

Typical Subaru rear suspension.

Posted by: horizontally-opposed Jan 29 2021, 05:06 PM

Open to all ideas, as this is all about spitballin' at this stage.

With that said, and pursuant to @mb911's post above, I actually think the suspension concepts of the 914 are pretty good. Sure, multi-link, double A-arm, etc are better when it comes to camber gain, etc—but 914s are plenty fast and able to process bumps even by modern standards. The light weight and long wheelbase definitely help. And, to my mind, the best solution is a part that bolts on—so it's a reversible mod. That broadens the customer base. Cutting the tub is a nonstarter for a lot of folks.

I reached out to an overqualified acquaintance who might be able to help with some early feedback on ballpark weight loss vs rough costs for the first pair of trailing arms (development, setup, creation) and then more in small qty. We'll see if he laughs me out of the room.

Meantime, also reached out to one of the 2-3 techs I would hire to rebuild/narrow/reinforce/five-lug/add 911 e-brakes/repaint/re-bush/re-bearing/etc for what he might charge. Asked him to do so on the basis of one stop, so no procurement on my side. First response: "$2500?" Then, as the scope of the work set in, "Could be more like $5k, with no brakes other than the parking brakes." Remember, this is checkbook math, not DIY—and some won't need to do some of those things, and can subtract accordingly, but checkbook math is the fair comp and I suspect $3500-5500 is a decent guesstimate for rebuilt/modded 50yo steel trailing arms.

Posted by: mepstein Jan 29 2021, 06:34 PM

Ben/MB911 might be able to give a good estimate since I think it’s in his wheelhouse
@http://www.914world.com/bbs2/index.php?showuser=9892

Posted by: mb911 Jan 29 2021, 06:48 PM

I would need you to put things down on paper or a picture.. I am more a picture book kind of guy.. Then I could give a real estimate.

Posted by: Chris914n6 Jan 29 2021, 08:24 PM

Cut down Boxster rear hub assm and just weld aluminum sheetmetal and tubing to copy the 914 arm mounting points/shock. Easy peasy and cheap.

Or maybe bolt the Box Assm to the AL trailing arm which would allow for toe and camber at the hub via spacers.

I'd also use a mass produced sleeved rubber bushing from another car/truck that presses in, example the Nissan Hardbody ft upper susp arm.

Whoever makes them can send me a set as payment

Posted by: andys Jan 29 2021, 08:52 PM

Having gone down the path of custom trailing arms (still mounted on my car), the more I studied the stock design the more sense it made. I also took a stab at aluminum, but only got as far as machining the bearing carriers. See post #32 at: http://www.914world.com/bbs2/index.php?showtopic=204625&hl=ls1%20retrospective&st=20#

Andys

Posted by: live free & drive Jan 29 2021, 09:19 PM

As a point of reference this thread on the weight difference between steel and aluminum 911 trailing arms is instructive:

http://forums.pelicanparts.com/porsche-911-technical-forum/192838-aluminum-trailing-arm-weight.html

Posted by: 914werke Jan 30 2021, 12:39 AM

Im sure its been documented somewhere on here before but as a point of reference using my bathroom scale: a OE 914 BARE (no bearings no shaft nothing) trailing arm is 15 lbs.

Posted by: rick 918-S Jan 30 2021, 04:39 AM

Anyone have a 914 arm they can post laying the same way this 911 arm is oriented?

Lets see what the two look like.

Posted by: horizontally-opposed Jan 30 2021, 10:31 AM

^ Now we're cooking with some gas.

Why replicate/redo/machine the trickiest part—the wheel/bearing carrier—when an arm can be made to accept a 911 or 986 wheel carrier? 986 is appealing as they're plentiful used or new, and engineered to deal with loads from 255/17 summer tires up to MY2000~, and 265/18 summer tires from MY2000~ on, when mounted on a 2900-3200lb mid-engined car. Wheel bearings availability is probably just fine and will be for a long time, and they're ready for 986 rear calipers and incorporate an internal drum e-brake. For the truly nutty 914 builds, there's provision for a lateral link (to the transmission?) and even a wheel-speed sensor for traction control.

Aluminum 911 trailing arms Rick just posted are out there new and used as well, but are probably in greater demand for obvious reasons. Might be sliced and diced to work, however, and also mounts 911 calipers/e-brake.

That would leave design of the blade/arm and front end. I suspect the outside cost on a pair of new arms has to be $5,000-7,500 before even a small group would consider them, and there will have to be advantages besides weight in order to make them compelling. Could it be done?

Posted by: horizontally-opposed Jan 30 2021, 10:47 AM

986 wheel carriers, Porsche-engineered, made in Italy by Brembo. Looks like a high-quality part. Available for $120-200 used, thanks to two per 996 junked and four per 986 junked.

I almost forgot about Porsche's cost-saving move to design these to work at the front or back of the car (LF/RR or RF/LR), which allowed them to use just two castings for all four corners of the 986. Wheel bearing, 986 caliper mounts, and integrated e-brake are all very nice—and I suspect this piece will be hard to beat for weight vs strength. Not sure what to do about that shock mount—could it be put to use via machining or custom shocks, or does it need to be removed?


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Posted by: horizontally-opposed Jan 30 2021, 10:58 AM

A couple more images.

The 986S and 986.2 went to a larger wheel bearing, I believe in conjunction with the 18-inch wheel approval (or near it), but the early setup was engineered and approved for a 255/40ZR17 tire at the back of a 3,000~ pound Boxster, and a 225/40R18 summer tire at the front of 996s. I remember a Porsche engineer saying this design was also an answer to problems with the front wheel bearings used on the front of 964 and 993 race cars—which had reached their limits with 18-inch slicks.



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Posted by: rick 918-S Jan 30 2021, 03:56 PM

My thought was to see if a 911 arm could be sourced and used as is with an adapter to the suspension ear and mount on the 914 chassis without cutting the car or the arm. My concern is the triangle the 911 arm forms when adding the flat bar may interfere with something. The 914 part does not form a triangle. Likely for a reason.

That 986 hub looks inviting...

Posted by: horizontally-opposed Jan 31 2021, 11:16 AM

Suspect the far wider triangle of the two-piece 911 trailing arms is afforded by the narrow transmission ahead of the axle line in a 911—the only way to do that in a 914 would be to reverse the trailing arms in a 914…an idea Porsche thankfully abandoned with its very first mid-engined sports cars in the early 1950s.

914 arm is triangulated, though to a much lesser extent…but that still needs to be considered and replicated.

Agree about 911 arm + modded 986 wheel carrier + some form of triangulation (that maybe doubles as a toe-adjust). Not sure it will be lighter if it's going to be cost effective, but it might be stronger, newer, and integrate a 986 e-brake, 986 caliper mounts, and wheel bearings in the bargain. I've never liked the idea of slicing the 914 trailing arm to add the 911 e-brake and caliper mounts. I know a lot of people have done it, and successfully, but I have also seen those conversions go wrong. 986 front calipers, meanwhile, are easy to adapt, and probably the best technical solution for a 914 (modern, light, stiff, cheap, plentiful, available for more and less power thanks to 986S, and set up for a mid-engined car rather than a rear-engined one). Only count against them is they don't look as period or as cool as 930 brakes…but the latter are big $.

I can't draw to save my life, but the Rennline outer 911 arms are only $250 a pair, while it seems like a nice pair of 986 carriers with e-brakes run $200-300 a pair. So the challenges will be figuring out mating the 986 carrier to an (existing? 911 outer?) trailing arm, the forward pivot/mount, hub placement, body clearance, and triangulation. Oh, and the stub axle, too. See? "Easy." Had an offline conversation yesterday, and a good engineer to speak with this about was named.

I wonder if the 986's "pinch" strut mount can be removed so a trailing arm can be made to attach the carrier and also locate the 914's lower coil-over mount.


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Posted by: horizontally-opposed Jan 31 2021, 11:26 AM

There are a lot of interesting starting points, from mild to wild, and perhaps one of these vendors could modify something they've got to suit and also provide integration for triangulation to the 914's inner mounting ear.





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Posted by: horizontally-opposed Jan 31 2021, 11:29 AM

Elephant offers a surprising number of choices—but I guess it makes sense as there's a lot going on at the back of a 911…

Was expecting these 959s of 911 spring plates to be $4-5k. They're priced at $2500. So the range from Rennline to 959 appears to be ~250 to ~2500. The wilder Elephant arm also makes a possible point (or two) for triangulation evident. Might have to be flipped side to side and/or modified to fit on a 914 to avoid the curved arm from interfering with the body.

Would I pay $2500-4000 for an arm like this, in a 914, vs $3500-5000 for rebuilt arms with all the tricks? Yes.


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Posted by: horizontally-opposed Jan 31 2021, 11:29 AM

And yet another option from Elephant…

Not sure I see the need for ride-height adjust with all of the kits available to do the same with 914 rear dampers, but then again, I still haven't bought one of those sets. Might be nice to fine-tune the ride height and even corner balance the car with my less than exotic Bilstein HD/Weltmeister setup—particularly if it's part of the bargain in a trailing arm upgrade. No need to replace springs I like with threaded sleeves and new springs of the same rate.


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Posted by: stownsen914 Jan 31 2021, 12:21 PM

A while back I looked into redesigning the 914 rear suspension for my racecar. The options are a bit limited due to the relatively wide flat 4 or 6 engine being in the way. A 911 trailing arm would be a great option, if you could get it to fit. But there isn't room for the inner mount.

Dual wishbone type suspension is an option, but of course would mean a lot of modifications to to the chassis. I've seen it done on a few tube frame 914 racecars. I've also seen stouter trailing arms like the ones on Sheridan's 914.

The challenge is twofold for the 914 - the trailing arms flex, and the chassis in the rear suspension area needs reinforcement too.

In my case I added a lot of tubing to the car when I built it to strengthen the chassis. The trailing arms are just stock one with the welded reinforcement kit. Someday when I re-do the rear suspension, I'm planning a custom trailing arm with the adjustments at the hub, similar to what Sheridan did.

Posted by: rgalla9146 Jan 31 2021, 02:19 PM

My GT conversion.
Is this lighter and stronger ?
If the trailing arm were re-shaped (narrow + taller ) could it accomodate the narrow
body wheel / tire requirement ?


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Posted by: 914werke Jan 31 2021, 02:44 PM

Gawd that's Purtty!

Posted by: mepstein Jan 31 2021, 02:48 PM

Rory also has some suspension console reinforcement that you can see in the pic.

Posted by: horizontally-opposed Jan 31 2021, 03:19 PM

Whoa! Never saw these. Very cool, and I'd be curious re: your questions.

I have no doubt that Porsche engineered (and overbuilt) the 914's steel trailing arms down to a price. I doubt it did so with a 50- to 100-year service life in mind, but there's no doubt they're long-life parts. I cannot remember hearing of a failure, but they were reinforced for racing by Porsche and others.

I do wonder what goes on inside of the boxed sections, as it's "unlikely" they were treated for condensation/rust any better than the 914's longs and center tunnel were. What did yours look like inside when they were sliced up, Rory?



Some very nice work indeed on Rory's car. That car keeps impressing me, visually and technically—how has it not been nominated for COTM yet? (Makes mental note.)

I've been considering the reinforcements below next time my engine comes out. The inner mount reinforcements are from Tangerine Racing, while the outer is from Patrick Racing. Like the idea of reinforcing the outer mount with the long, but wonder what an engineer with relevant experience might say—and don't love having to remove the rocker panel to adjust if that's what would be necessary. The factory did some interesting things with rocker panels on some of its rally cars, including leather straps to allow the back of the rocker to be peeled open for field service. Looks cool on a Monte Carlo works GT, but zero interest in that for a road car.




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Posted by: rick 918-S Jan 31 2021, 03:56 PM

Some of that 911 gear looks like a Rube Goldberg devise. I having a hard time imagining those parts not flexing (twisting) under a torsional load.

Posted by: rgalla9146 Jan 31 2021, 04:33 PM

Simple triangulation of inner ear and in the case of the rear trunk increased
cross section of transmission crossmember.



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Posted by: eeyore Jan 31 2021, 05:01 PM

@http://www.914world.com/bbs2/index.php?showuser=1444 Any thoughts?

Posted by: rgalla9146 Jan 31 2021, 05:05 PM

As for Petes question about internal condition of the trailing arms.....
mixed answer. Upper surfaces were perfect (dip painted even ? !) some bottom areas had some surface rust.
They are not a closed chamber, they all have holes manufactured in. My only regret is I didn't use seamless chromoly tubing.
Notice the grinding on the brake adjustment tube. That is necessary for GT spaced calipers to be centered over rotor.


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Posted by: horizontally-opposed Jan 31 2021, 05:12 PM

^ Really nice upgrades, Rory.

Posted by: horizontally-opposed Jan 31 2021, 05:16 PM

Haha. Can't disagree, though I am not qualified to comment. With that said, the $250-350~ pair of spring plates with ride height adjustment might be a better starting point than $2,500 moon gear. Narrower, too. And if camber can be adjusted at the wheel carrier…or just stick with the shims, which work fine.

One thing I am noticing in looking at images of the 901/911 tub is that its upside of more room inboard for that banana arm appears to be offset by the way the 901/911 tub drops down—the 914 has more room for its one-piece trailing arm. Need an engineer to tell us which is "better," if one is, but if there's one thing I have learned while studying Porsche, it's that the 914 benefitted from another 3-5 years of learning at Porsche—not to mention the skyward engineering ambitions of a young Ferdinand Piëch. Yes, that one—the 917, Quattro, and Veyron guy. Also, the Phaeton… 


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Posted by: horizontally-opposed Jan 31 2021, 05:36 PM

And then you consider the work that people are doing to 914 trailing arms, more often than not reinventing the wheel on their own as they do so…with the photo below as seen in Armando's wonderful "The last new 914-6 GT thread" over on the Bird Board…

Poking around, several shops offer rebuilt trailing arms from $850~ with no bells and whistles to $1800 with 911 e-brakes & four lugs or $2400 with 911 e-brakes and five lugs.


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Posted by: groot Jan 31 2021, 06:12 PM

Me? Lots of thoughts... about what?

I expect the 911 blade-type semi-trailing arm was more expensive (more complicated, more parts, etc), so the 914 version is cost-reduced version of the semi-trailing arm and took advantage of the 914 package space. They are both less than ideal for proper race cars... but, it can get worse.

In the end, they both have the same limitations (toe/camber/roll center/static camber are all intertwined). Camber gain is minimal and the roll center gets way too low with increased negative camber.

Responding to the original question with some commentary:

• Move the brake line
• Tire clearance can be pretty minimal at the trailing arm, I'd be okay with 5mm
• If you can't get to 5mm, you may consider scalloping the trailing arm, while adding some stiffening actions

Posted by: 914forme Jan 31 2021, 08:03 PM

I have been thinking about this a lot, and came up with several solutions but they achieve nothing. As just posted there are a bunch of issues with the rear arms on both the 911 and the 914.

I had a set of the best arms ever made from Tangerine Racing. And they had a bit of clearance issues with 17 rears. Chris said dent the gusset he puts in there.

Here is my thoughts going thiner you have to increase strength in some way. Thicker walls and internal gussets but these do nothing for the inherent geometeryissues that come with running the arms.

If you want lighter get a set of arms made out of Titanium. That would also allow you to narrow them.

If you really don't care what they look like under the car, a series of laser cut sections could be made and significantly reduce the thickness of the area while adding to registry.

If you did this out of aluminum then you could weld on a modified 986.2 rear console and all the great bits that go along with it.

Lot of TIG time to build it.

In reality have someone 3D model it, send it off to be 3D printed as a sand cast mold, and then build the parts of your dream. You get one shot with the mold. But it works.

Posted by: barefoot Feb 1 2021, 11:45 AM

Making trailing arms out of titanium or aluminum won't necessarily buy you anything of value.
Stiffness is the major design requirement for a trailing arm and for a given mechanical design (ie the present dimensions od the 914 arm)
While aluminum is only 34% as dense as steel, it's only 34% as stiff as well, so specific stiffness (Tensile modulus divided by density) is 106 for 7000 series alloys.
6-4 Titanium alloy is 56% as dense as steel boy again is only ~62% as stiff, so specific stiffness is 101.
carbon steel is more dense, but much more stiff, so specific stiffness is 106. so for a given geometry you'd have to make the wall thickness much thicker in aluminum to achieve the same stiffness, same for titanium, so no weight savings.
Only changing the arm geometry (like a bigger box section, or the clever tube inserts seen in these posts) can improve it's stiffness.
Higher strength alloys don't improve stiffness, just allows greater deflection before permanently bending.

Posted by: horizontally-opposed Feb 1 2021, 01:03 PM

^ Good inputs.

Would be curious for an engineer's take on Rory's very cool looking solution, but figure that's only added labor on top of the rebuild/reinforcement services available for $1800-2400 once a 911 e-brake is grafted into place. Also wonder how much weight that saved, Rory? I sure dig the look…

$2000-4000 for a pair of modified 50yo trailing arms would seem to open up possibilities for new trailing arms—and perhaps some weight savings come instead from 986 or 930 calipers instead of two-piston steel Ate calipers and/or two-piece rotors. But it's going to take an engineer to see a smart way forward.

Posted by: eric914 Feb 1 2021, 03:28 PM

Ive just skimmed though this thread but it presents an interesting. I don't believe that the 911 spring plates see any lateral load though, it is just transferring the force generated by the torsion bars. The aluminum suspension arm takes all of the lateral loads. In the 914 the spring plate would be eliminated and a coil over shock used in its place.

Posted by: rgalla9146 Feb 1 2021, 05:43 PM

Doooh! I didn't weigh before and after. But....
I wanted to add stiffness in a different way.
The commonly available kit was not appealing to me.
Our cars have virtually no multi-layer metal features or reinforcements.
They do have complex shapes and boxes which provide very strong lightweight
assemblies.
My picture shows what was removed and what was not added.
What was added was maybe 1 1/2lb. of heavy wall 2" and 3" tubing.
The stiffening kit and removed discs weigh 2lbs 14oz.....~3lbs then
1 1/2 lbs went back on.
So a net loss of 1.5 lbs per side. Unsprung.
What really matters would be performance in a torsional rigidity test.
That can not be done with a postal scale





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Posted by: stownsen914 Feb 1 2021, 05:50 PM

If you're fabricating and really want light, I believe the best racecar fabricators use chromoly. It's not lighter than low carbon steel, but you can use thinner wall to get the same strength. I suspect most just use DOM steel since it's easier to work with.

Posted by: rgalla9146 Feb 1 2021, 06:07 PM

next time it will be chromoly and TIG

Posted by: 914forme Feb 2 2021, 09:53 AM

I while I agree with you on your basics, it is the design that forms the ability to make the part structurally sound beyond the pure metallurgy, You have to know what you're doing with the Alloys to make this work.

I was never implying it would have been built the same as the 914 stock steel carbon arm.
But that you are limited in the design due to the factors placed onto via the chassis.

Posted by: 914forme Feb 2 2021, 10:32 AM

Pete While I find the topic intriguing I wonder what the real end game is.

Tire technology has outpaced suspension design over the last 50 years. So now unless you racing competitively in auto crossing at the national level I would not worry about 10mm of sedition width.

Slap on a set of DOT R compound tires, add a set of fender liners, and go drive. The fender liners are needed to avoid the small upward dents you get from all the rocks flying up under the fenders. As little as people drive their 914s you get years out of the tires. And well they are way better than the Dunlops my dad had to choose from in 1976 when he got his 914-6.

Remaking the arm, while possible would exceed the 2-3K you would spend to have an arm customized. Via Chris.

Or you can do Rory's design and it works also, just to a lesser degree than Chris' solution, but it does provide a solution that can easily be done in your garage.

I had an idea on how to duplicate Chris efforts, but chose to pay him for his intellectual property. Sometimes it is worth supporting the vendors that make this hobby what it is, and the community.

Posted by: 914Toy Feb 2 2021, 11:17 AM

While repairing damage to my 914's passenger rear quarter caused by a texting driver crashing into it ,repairs required a good used replacement full quarter panel and trailing arm. I recall one "expert's" comment that the trailing arm strength and design included minimizing damage to the tub in the event of such damage. This worked for me. So, perhaps strengthening the trailing arms along with weight reduction should not be done for our street cars, but may be helpful for track cars.

Posted by: burton73 Feb 2 2021, 01:51 PM

Sorry for my mess on my pouring table but this is a PMB (E) modified strengthened trailing arm done 10 years ago. Weight 25.5 LB with 930 turbo Stub Axels, 911 early parking brake, Elephant Polly Bronze and well what you see.

Bob B

Posted by: horizontally-opposed Feb 2 2021, 03:19 PM

End game is:

1) "Right-sized" footprint: I've had virtually every 15-inch tire size that will fit into a narrow 914 under my car. Current rubber is Avon CR6ZZ, a vintage race/rally tire available in three compounds, so about as grippy as you'll get. 185/70 all around is just okay; with RS 2.7~ power, I'd like to run a similar tire package without resorting to M471 flares or a repaint. Suspect there are others in the same boat with 2.7s, 3.0s, 3.2s, etc

2) Performance and looks; 215/60 seems to me about right for what I am after in terms of performance, and I think it would also look great on the car. 225/50R16 also offers fantastic performance and looks great tucked into the back of a narrow 914.

3) Tire choice; 205/60R15 tire choice is far from great; factory tire sizes offer prospect of more availability & choice over the long haul; 195/65 & 215/60 or 185/70 & 215/60 offer period looks and at least three great options for the street. If there's space for 225/50R15 or 225/50R16 in the rear, unlocking some great R-compound tires, that's a bonus. My test fit suggests modified trailing arms and a bit of fender pull might make it work.

4) Cost to rebuild/modify old arms: Prospect of spending $2000-4000~ to redo another set of 50yo trailing arms with little to no technical upside isn't interesting. 911 e-brakes and aluminum calipers wasn't appealing, so I wanted to get some feedback from the community on whether the time has come for another option.

Fully agree on rewarding vendors in the 914 community, and have sent a fair bit of business their way over the years, but perhaps a new trailing arm might be more profitable for them than modding old ones? Fortunately, smarter people than me (!) are spitballin' this now. Carbon was an early casualty due to setup costs as well as actually popping them (not to mention liability and potential inspection/longevity/etc), and I suspect Ti is out due to $$, too.



Glad you raised this, as it was on my mind at one point. Worth paying attention to if there's a solution—as I'd far rather lose an arm than a car!




No apology needed! Another great input & data point. 25.5 with all that we see there is not bad, not bad at all. Maybe the goals shift to cost of upgrade ($2000-4000~ rebuild vs $250-500 custom spring plate + triangulation of some sort + used $100 986 carriers, etc) with any weight saved or additional clearance for a 215 or 225 tire as gravy.

Posted by: mepstein Feb 2 2021, 04:10 PM

I'm still confused when you say $2-4K to redo the trailing arms. Rory's mods are cool but I doubt they make much difference in handling and I can't image a narrow body street car needs stiffer trailing arms.

There's a lot of low hanging fruit on a 914 that can be improved before you spend the big bucks on diminishing returns.

There's no way to fit 225 in the back without fender mods.

Michalin TB15's ?

Posted by: horizontally-opposed Feb 2 2021, 04:23 PM

Seeing $1800-2400 listed on websites for "standard" rebuilds with 911 e-brake and/or stiffening, and suspect that's a result of jigs and knowhow. Had a fabricator I like suggest all that plus reinforcements and scalloped for a bit of tire clearance plus the 911 e-brake etc could run $4000-5000.

Do like Rory's setup, but if the knife comes out, I'm going to 911 e-brakes too—and I've seen those go wrong.



Agree. If I redo mine (again), I probably won't reinforce.



Agree also—but 31 years in, I'm through a lot of the low-hanging fruit short of a lightweight battery (on the list) and non-steel body parts (probably not for this 914). There are actually a few places I will add a bit of weight to increase usability—mainly radio and heat. But I like the idea of offsetting that…and am slowly (!) planning my next suspension rebuild.



It's been done with what I'd still call minor fender rolling/pulls—and not just once or twice. I've seen 215/60R15, 225/50R15, and 225/50R16 on the back of NB 914s over the years. Sometimes hacked, sometimes not—and sometimes not at all. One 914 six conversion claimed to have 225/50R16 under stock rear fenders—not sure I believe they are completely stock, but it's clear they used 16x7 Fuchs with custom offsets.

As for Michelin TBs, 215/55R15 could be good for some cars—and are certainly viable for the front of an M471 car. But they're a bit "short" for a narrow body (to my eye), and I've heard from friends who ran them on street cars that they aren't so easy to live with—being noticeably worse than the Avons in that regard. Tried them on a 914 M471, and they sure offered sweet steering and plenty of grip. Same owner wasn't so happy with them later on.

Posted by: rgalla9146 Feb 2 2021, 05:25 PM

I may track my car one day but it will never have slicks.
My arms will never be scientifically tested.
I feel empirically that I've added stiffness.
Do I even need stronger arms with my current tires ?
The modifications are for my own satisfaction.
There is of course artistic and technical pride.
Absolute maximum tire ? ...... maybe in the future, right now I have a combination
that is quite enough. A more powerful engine may change that.

Posted by: mb911 Feb 2 2021, 06:04 PM

God I am too cheap on everything I do..

Posted by: Mikey914 Feb 2 2021, 06:16 PM

The problem becomes that these items can get very expensive very quickly. Especially if you do the engineering. We are currently working with a known suspension company that makes race suspension to offer up a kit. We are hoping that thee may see the light of day in summer. We had thought about getting into this market, but when you start jacking up loads beyond the factory spec things can get dicey. This is why we offered to handle distribution once they have a turnkey kit.

Time will tell.

Posted by: Superhawk996 Feb 3 2021, 07:52 AM

If you're running this kind of power, a narrow body car seems like a non-starter to me. HP without the ability to ground it is nearly worthless. Yes, modern rubber makes up for some limitations of tire size but let's not forget that when the factory moved to GT style horsepower, the flares were put there for a reson. Form follows function.

Once you go to flares, it solves the tire clearance problems.

There are other benefits that come with flares and the ability to run staggered tire sizes to balance the car. High HP needs more tractive effort at the rear while simultaneously offsetting the tendency toward throttle induced oversteer and drop throttle induced oversteer.

My point being the flares aren't an afterthought or for styling, but, are part of an engineered solution to manage the horsepower and balance the handling. Seems like you're after a complete re-engineering of the suspension in order to avoid flares and a repaint. I'm probably missing something else.

Of course, by my avitar photo, you'll notice I'm biased.

Posted by: barefoot Feb 3 2021, 08:28 AM

I would expect that Porsche intended the trailing arm to be the sacrificial element in a collision rather than the suspension console.. So agree for a street driven car reinforcing the trailing arm may well lead to much more expensive collision repairs.

Not sure how sophisticated structural analysis was back then, but now everything is modeled in 3D graphics which makes finite element structural analysis easy, so designers now can see exactly where deflections occur and design accordingly.

Posted by: barefoot Feb 3 2021, 08:44 AM

The large diameter tube reinforcements are a much better design than the small tubes seen in some other mods.
Remember that the stiffness of tubing increases with the 4th power of diameter. So you could have a much stiffer mod and lighter by using thin wall tubing.

Posted by: horizontally-opposed Feb 3 2021, 03:29 PM

Good points, and fully agree on the ability to put the power down (in general) as I enjoy a handling car over a power car. Of course, I don't mind when they're got both…

Some quick thoughts re: your thoughts of "this level of power" and narrow bodywork:

1) I'll take the blame for noting hp vs lb-ft when torque is what really matters, but nevertheless feel 185/195 & 215/225 15-inch and 205 & 225 16-inch are a good tire package for RS 2.7 > Carrera 3.2 power/torque. Porsche engineers—no dummies—also seemed to think so, and used those sizes on 911s with up to 210-230~ hp and 180~ lb-ft from 1973 through 1989, and then again with the standard 16s on the 1997-2004 986 with 200 hp/181 lb-ft—a car that is 700-900 lbs heavier than our 914s. Also: Tires today are better than tires of the 1970s, 1980s, and even the late 1990s/early 2000s.

2) The factory's decision to flare the competition 914-6s probably had more to do with increasing track and lowering lap times than an inability to put the torque down—as the 914 ran in the 2.0- and 2.5-liter categories and didn't have a lot in the way of torque, something that's never been the strong suit of Porsche's normally-aspirated flat sixes. We only think of the 3.0-4.0 engines as "torquey" because they are—relative to the 2.0-2.7 engines, anyway. But even the hottest NA flat sixes making 500+ hp post up pretty meager torque numbers against other engine configurations making 500 hp.

3) I have a fair bit of seat time in cars that can easily overwhelm their driven wheels. More often than not, they aren't my thing—I'd much rather have a car that handles well than one set up to spin its tires. Probably why I like 914s so much. My take with my 914 is that 185s in the rear, even very grippy vintage race tires, is almost CGT-ish (in a very perverse, CSOB way. ) Put another way: It doesn't feel all that reassuring. First step in optimizing my car's handling is tire selection, hence a lot of thinking at this stage.

4) I don't claim to be "right" about this, as it's absolutely a best guess, but 20+ years of testing all sorts of Porsches + studying their development + speaking to the engineers behind many of them has me thinking 185/70 or 195/65 & 215/60 (15-inch) or 205/55 and 225/50 (16-inch) is a good setup for a narrow 914, neither over- or under-tired for a 914 with 180-230~ hp. Fenders that will accommodate would also provide space for 205/50R15 and 225/50R15, opening up a great selection of autocross and track tires—or maybe even 225/50R15 square, which was on what remains probably the best, most fun 914 I have driven.

5) Big six, as in 3.6, 3.8, or 4.0? Yeah, I'd want GT/M471 flares—but I don't need a big six in my 914 and don't want to flare this car. I wouldn't call narrowing my arms, or wanting to see a product for 914s like those for 911s, a complete re-engineering. One could argue big sixes, flares, and 245mm+ rear tires will prompt something much more like re-engineering of the 914. In exploring ideas to add 5-10mm of space where the 215/60 hit my trailing arms, I started to wonder if there's a better solution than doing what's been done to 50yo arms in the past.

The bodywork is no big deal, and has been done quite often. 225/50R15 has been snuck into a fair few narrow 914s with minor pulling/rolling, and 215/60R15 has been too. Still trying to nail down what was involved in sneaking 225/50R16 into http://www.retromodcars.com/features/sleeper-914/6-this-stock-looking-914-hides-a-993-engine. At the time I commissioned an article on the car for Excellence, it sounded like custom offsets + trailing arm tricks. Reading the piece above, I do wonder about the fenders…but whatever was done, it was subtle.

Bottom line, I'm interested in "adapting what I have." If I can sneak a 215 into my rear fenders with some pulling/rolling, that's a lot more attractive to me than welding on GT flares and changing the shape of my car—and I'm not sure the idea that the right answer is always GT flares, particularly for "small" or "mild" six conversions (i.e. warm or hot 2.2-2.7 or stock 3.0/3.2). Judging by the page views on this thread, I may not be alone. Now add in the brake and stub axle upgrades most people do with a six conversion. If we're gonna have to do it anyway…

Posted by: horizontally-opposed Feb 3 2021, 04:02 PM

From the link above:

The 16x7-inch Fuchs that the 914 rolls on may look stock, but they’re actually custom items that were made by Harvey Wiedman of Wiedman’s Wheels in Oroville, CA. “Having run aftermarket seven-inch rims on my race car, I knew 225s were possible,” explains Wolcott. “I also knew I wanted the classic Fuchs wheel. However the key to seven-inch rims with 225s on an early narrow-bodied car like 911s, 912s and 914s is the backspacing. Unfortunately, while made Porsche made seven-inch Fuchs, they never made one with the backspacing I needed, which is where Harvey Weidman came in.”

When Wolcott made a call to Weidman, it just so happened that Weidman had been dealing with a similar dilemna for his own early 911. “He had just finished work on a set of prototype wheels for his own early-bodied 911,” continues Wolcott. “He said once he shook down his own set, if all went well, he’d do a set for me. The way he described it, it was taking two sets of 16 x 7 Fuchs, cutting each in half, then welding the appropriate halves back together.” The outer rims pf the wheels were polished and the centers powdercoated to match the 914’s custom badging. Tires are BFGoodrich G-Force KDs that measure 225/50ZR16 at all four corners.


Attached image(s)

Posted by: horizontally-opposed Feb 3 2021, 04:04 PM

From our own Bruce Hinds:

I'm running Falken 215/60 x 15 all the way around. The wheels are 911 SC phone dials, 15 x 6 on front and 15 x 7 rears. As I understand most 911SCs had the 16" Fuchs, but that was an option and the phone dials were standard.

I did stretch the rears with a bat to get them to fit, but it's a nice set up. When I get new tires I may go 205s up front, I've been told the 215 is a little wide for a 6" rim.


Attached image(s)

Posted by: horizontally-opposed Feb 3 2021, 04:05 PM

From our own Keyser Sose:

Here, some 215x45x16 on 7" 911 SC Fuchs, front and rear:


Attached image(s)

Posted by: horizontally-opposed Feb 3 2021, 04:07 PM

Also from our own Keyser Sose:

And my son's car, 225x50x15's on 7” 911 cookie cutters:


If I remember right, this car had to have the fender support ahead of the LR cut and rewelded to allow the fender to come out of bit, where the RR fender did not require it.

Obviously, the less you have to pull, the better—which is also part of why I am looking at 911R offsets, custom spacers, and narrowing the trailing arms.


Attached image(s)

Posted by: Superhawk996 Feb 3 2021, 04:20 PM

Nice set of well thought out counterpoints! You and I are on exactly the same page on point #3; I'd much rather drive a well sorted car than one that spins the tires in all the wrong places.

I tend to agree that you'll have more success managing tire fitment via custom rims and backspacing.

Double bonus points go to the picture of the 914 with the raft on top. Love crazy strapped to the top of sports cars. I have a long history of doing similar things.

Posted by: brant Feb 3 2021, 04:24 PM

James' car. I haven't seen it in a while. An amazing car built by a father and son
James moved back to NM a few years ago, I haven't seen him since. We used to race against each other a lot with his track car

Posted by: mepstein Feb 3 2021, 04:26 PM

If a custom Wiedman wheel takes two Fuchs, cutting, welding and finishing to make the end product, I'm guessing 300 each wheel, 400 to cut and weld, 300 to finish, 50x2 to ship each way. $1,100 + per wheel - My guess.

Posted by: stownsen914 Feb 3 2021, 04:38 PM

So there are multiple problems with the stock rear suspension. Addressing all of them isn't trivial. In no particular order:
1. Rear chassis is weak/flexes
2. Rear trailing arms are weak/flex
3. Rear suspension geometry isn't great. The roll center is relatively high, camber gain is less than ideal, it toes out as the suspension moves in bump, and has more scrub (side to side movement as the suspension moves up and down) than ideal.

1 and 2 require fabrication, but are possible without doing crazy mods, and can be a significant improvement for a racecar, or a car with a lot of power. #3 is harder because you have to change the suspension pickup points (major chassis mods) and build all new trailing arms. A big project.

I did a bunch of suspension geometry modeling for my racecar using a program called susprog. I actually redid the front using newly fabricated struts and A arms and all new pickup points. Made a big difference in the car's handling. (On the rear I basically did #1 and 2 above when I built the car.) I haven't redone the rear yet since it's more work. Someday ...

Posted by: horizontally-opposed Feb 3 2021, 04:38 PM

Probably about right. Harvey can likely widen my deep sixes without refinishing the fronts, but not sure I want to cut them.

Or one can just buy these, new and ready to go, for $500ea:
https://tremotorsports.com/exterior/fuch-style-deep-6-7-wheels

Selling a set of 15x6 flat Fuchs that are less than perfect would go a long ways or even cover a set of these.

There are also these:
https://www.stoddard.com/91136102011-rpb.html.html

From everything I can see, these are high-quality wheels, made for rallying and circuit racing. $435-500ea seems strong value to me.

Posted by: rgalla9146 Feb 3 2021, 04:39 PM

"The large diameter tube reinforcements are a much better design than the small tubes seen in some other mods.
Remember that the stiffness of tubing increases with the 4th power of diameter. So you could have a much stiffer mod and lighter by using thin wall tubing. biggrin.gif "

Wow. Thank you Mr. Barefoot

Hey Pete how much do you need removed for tire clearance ?

Posted by: horizontally-opposed Feb 3 2021, 04:46 PM

Great inputs here.

Still think 986 wheel carrier idea from Chris has legs. Someone has pointed out that it has Weissach Axle geometry, but that's passive/active through the arc and I am not sure it matters if the carrier is literally just a carrier and rigidly attached to a trailing arm. Someone else pointed out that machining off the 986 carrier's strut mount may affect its strength, something that definitely has to be considered, but again the right trailing arm could account for that—and provide a lower mount for the 914's damper—maybe height adjustable for lowered cars?

So everything comes down to the trailing arm. I look at Tangerine's pickup point relocation kit and would do that in a second on a race car. I look at the trailing arms, and wonder what possibiities for correction with new arms. And if they're black, and not not blatantly hideous, one suspects there are some interesting corrections to be made. Look how far the 1964-1989 911's rear suspension was developed—both by Porsche and the aftermarket. Now consider the fact that, more often than not, even many 914 race cars have been built around trailing arms optimized for the 1970 914 & 914-6 and never revisited.

The engineering and construction of new trailing arms is way past my pay grade, but already this thread has brought out some interesting ideas. Worst case, I narrow/scallop some stock arms and sell mine. But one can hope…

Posted by: horizontally-opposed Feb 3 2021, 04:48 PM

Would have to really look at it, as the answer is "kinda" important, but after relocating the brake line…5mm? Maybe a bit more?

Posted by: 930cabman Feb 3 2021, 04:56 PM

Exactly, the engineers who designed our 914 probably were not planning on 225 or any wide tires, OR the loads wide tires will impose on the suspension/chassis/etc.
This is my first 914 and I am planning on going with 185 tires, to take advantage of the "wiping" technique described from 356 sporting drivers. But I am old school

Posted by: mepstein Feb 3 2021, 05:08 PM

It's tough to put fake Fuchs on your car once you have real ones. They look similar in pics but not so good in real life. And most are heavier.

Posted by: horizontally-opposed Feb 3 2021, 05:15 PM

Agree with your logic (as usual), but two things:

1) These aren't like the Fachs of the past, in quality or "almost" appearance—or, for that matter, focus on appearance and cheap cost. The Group 4s, in particular, look very close (probably close enough for me…still mulling having Harvey widen two of my 15x6s—but that brings up other questions).

2) My research indicates they're within a pound of forged Fuchs, and made by companies that supply rally wheels—so they appear to be quite strong. One can argue the merits of new cast 15s vs 50yo forged 15s with unknown # of heat cycles, impacts, etc. til the cows come home. I can see it either way, and it's probably six of one, half a dozen of the other.

Or one can look at it more simply: I'd rather have the tires I'm after on good (or good enough) wheels than be stuck with tires I don't want on real wheels.

Posted by: stownsen914 Feb 3 2021, 06:03 PM

I'd actually say it comes down to the trailing arm and also WHERE you attach it to the chassis. The relocation kits I've seen are an improvement over stock, but as far as I know they still assume a stock trailing arm. If you're building a custom arm anyway, there is a lot of improvement to be made by moving the pickup points around (not just moving them upward). It would need to be modeled to do it right. There are a few suspension analysis programs out there. I used susprog, but I believe there are others. Some of the changes that gave me the results I wanted were not intuitive at all. And of course there would be a lot of cutting and welding involved once you design it.

Scott

Posted by: rick 918-S Feb 4 2021, 07:51 AM

I have a question. Does anyone think we are pushing our suspension and chassis design in spirited street driving beyond the design limits?

I have never added chassis stiffeners or even anti-roll control to my Alien. I drive the hell out of it. I have to admit the torque kills the traction. I can throttle steer the car even with 255/50/16's on 9's on the rear. Maybe it's all the years of winter driving or something.

I guess I am wondering out load about the amount of re-engineering of a really good stock design. I am of the mind that on a narrow body car the design allows for a manageable spirited driving experience. Even on track day.

When I did the 7 of 9 I never felt I needed to do anything other than be sure I was in the right gear to stay in the torque zone. (narrow, factory anti-roll, 2.0 FI. Lightened flywheel) The lightened flywheel allowed for faster spin up but killed the inertia.

I agree it would be nice to have a low cost solution to trailing arm clearance. But my seat of the pants tells me we are discussing an option that would provide very little benefit for a cost well beyond a set of custom wheels.

I am all in for a low cost nip/tuck on the trailing arm though. Simple 914 solution to increase the foot print without the Rube Goldberg approach to modification for the sake of saying we did something.

I understand the desire for wanting more. The conversation started out as the need for tire clearance. I am wondering with the right compound on track day if the narrowed stock arm would be enough. Lets face it. I am not sure a redesigned trailing arm will stop the throttle lift spin condition when corning too hot. LOL! I think that is a bigger problem..

Great topic though. Just goes to show how great these cars are when we have to debate the benefit of changing something from the original design.

It is also a discussion on unsprung weight. Question: Is there always benefit in reducing unsprung weight? I feel like I should know the answer but alas I am just an old hot rod guy that fell into the seat of a 914 and never had a desire for the old iron again.

Posted by: mepstein Feb 4 2021, 08:22 AM

Pete - Would adding an LSD to your trans help you.

Posted by: horizontally-opposed Feb 4 2021, 09:24 AM

So many good inputs and gut checks here. Maybe someone can point out the blind spots, but I see them falling into three primary categories:

1) Handling dynamics
2) Engine power output and delivery characteristics
2) Driver skill/style/preferences

That last one is a biggie. Actually all three are.

Agree this discussion only highlights how great these cars are—and it's generally accepted that less unsprung weight is better (so long everything is strong enough, etc). This discussion has moved me away from the drive to reduce weight on the trailing arm—though any savings, even minimal, would of course be nice—if other objectives can be met.

This thread has me thinking the better/more likely place to reduce weight—both unsprung and rotational—is the steel caliper and one-piece cast-iron brake rotor. The only reason I've stuck with the [/u]hefty stock calipers is to have an e-brake, and all these photos have reminded me just how smart the 911/986/etc drum-brake e-brake is, by doubling the use of the inside of the brake rotor's "hat." Looking at the e-brake on the 986 carrier, it really doesn't look like a lot of extra weight. I also wonder if an aluminum hat is mechanically viable with a drum-type parking brake?

Another option for an e-brake is the RSR type clamp offered by Zuffenhaus alongside their insanely cool and period-right RSR/917-style finned calipers, but I am afraid these are simply outside my budget against 986 calipers…especially used/refurbished ones. And I'd switch to four-piston 986 calipers in a second, as I've also learned one of my other preferences: I prefer a sports car that's "over-braked" to one that's "under-braked," and have run into fade in some pretty serious machinery. You can always drive around it, but I don't like serving my brakes' needs—or even thinking about them—when pressing on.

Posted by: horizontally-opposed Feb 4 2021, 09:30 AM

Doesn't really affect my interest here, as the desire to go to 185/215 is about stability and handling dynamics in all conditions over an ability to put the power down. The latter is controlled with my right foot, and has been a non-issue so far.

An LSD is on the list, however, for whenever the transmission comes apart next as a good one does offer some stability/predictability advantages.

Posted by: rick 918-S Feb 4 2021, 11:13 AM

Here is a thought to reduce unsprung weight. What about a smart conversion to inboard brakes like the Jags have. This may be an easier conversion than anything we discussed to date.

Posted by: mepstein Feb 4 2021, 11:42 AM

I'm not sure what Pete has on his car now but if they are ATE steel calipers then going to 3" Brembo or 3.5" S calipers and PMB aluminum 914-6 calipers would save 8-10lbs.

I know the PMB rears are nla but there are always parts available if you look and ask.

I am still in the belief that front suspension is 75%, rear 25% so tuning the front suspension is more important. That's from my bike riding and racing experience so I realize I have a huge knowledge gap for cars.

Posted by: ClayPerrine Feb 4 2021, 12:04 PM

There are at least two problems (that I can think of) with inboard brakes....

1. U-Joint/CV Joint Windup. It puts more load on the CV joint due to braking, and that causes windup in the drivetrain.

2. Heat Dissipation. It adds heat inboard where there is less airflow, causing both brake fade and possible other heat induced problems with the transmission.


I think the benefits of less unsprung weight are outweighed (pun intended) by the drawbacks. If it were a huge benefit, we would be seeing inboard brakes on a lot of modern performance cars.
Clay

Posted by: rick 918-S Feb 4 2021, 01:01 PM

Ya, you would need to change to real U joints like the Jags and Corvettes. I see the issue with the CV's

Posted by: horizontally-opposed Feb 4 2021, 01:14 PM

^ Yep on steel ATE rear calipers. Have 3' Brembo aluminum calipers up front that I guess could be moved to the rear if there are 911, 986, or RSR-type e-brakes, leaving room for a caliper upgrade up front. Would need to research what would be balanced with the Brembos if they move to the back. Or just go with a f/r system that's matched, whether 986 or 930.

But first, need to know what I am mounting said rear calipers to.

Losing 8-10 pounds would be worthwhile, and might be increased with the right rotors. I had a race shop drill my "hats" last time around, partly to cut a little weight but mostly for the fun of it…as it's a little detail I like on the 917s (not to mention modern Audis…with the common denominator being Piëch). Could a pound or two be shaved from each trailing arm? Or 3-5? Or maybe new arms would be even steven or even a bit heavier but offset by aluminum calipers and new features. Too early to tell, but a bit here and a bit there can really add up—and a lightweight battery plus 10-20 pounds out of the rear suspension and brakes might offset 30-50% of the weight gain with my six conversion in roughly the same area of the car, and I do miss the light, tossable feeling of my car as a -4.

Agree on importance of front suspension, but might put it closer to 50-75% (not sure where it falls, but I'd put it closer to 50%). Believe me, I have ideas for the front suspension, too. The difference is: Great options exist and are readily available—it's just a matter of budget…and figuring out what it will be paired to in the back!

Posted by: horizontally-opposed Feb 4 2021, 01:22 PM

Yep to all that.

Posted by: mepstein Feb 4 2021, 01:44 PM

A light battery is definitely low hanging fruit.

Posted by: Chris914n6 Feb 5 2021, 03:10 PM

996/997 rear susp. Would make sense to fab a steel subframe that fit under a 914 that had the wheels tucking appropriately. Use the 914 axles if possible. Welding to the chassis would make it much stronger back there.

Remove the no longer needed inner trailing arm mount and a Boxster engine should fit. But that is a whole different ball of wax. But then you could likely do a Porsche -6 swap for $10k all in...

Ignore the red circles... best pic I could find quickly.

Posted by: rgalla9146 Feb 5 2021, 04:40 PM

I love the idea.
......those upper links will extend well into the trunk/wheelhouse.
We're looking at the drivers rear hub from the roll bar down
.....but not exactly a DIY solution

Posted by: horizontally-opposed Feb 6 2021, 10:32 AM

I can see it for those willing to cut up their chassis and/or go to something other than a Type IV or 901 flat six, but will probably push the wheels well outside of the fenders outside of a narrow body 914 and require either modern wheel offsets even with M471 flares.

I've been thinking about your idea with the 986 carrier ever since you posted it, and the more I think about it, the more it makes sense. I even looked at whether optional lateral links could be adopted somehow, maybe off of a "saddle" added to or above the 901 or the transmission mounts, but it looks like an unnecessary complication and not sure the geometry would work out anyway? And I'm not sure the 914 suspension concept needs a rethink, though? It works well enough to have put these cars into the winner's circle for decades, and their handling is (rightly) legendary. Its execution, to a price, can be improved upon, however—just as with older 911s.

Anyone taking this on as a vendor needs to maximize market interest…and that's going to be for something that a) bolts on, b) doesn't require unibody mods, and c) is true to factory concepts and price sensitive (cap is somewhere around or a bit more than "the works" + 911 e-brakes on an old pair of 914 trailing arms).



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Posted by: ClayPerrine Feb 6 2021, 11:50 AM

I did the research on putting a Cayman rear suspension under a 914.

The track is about 6 inches wider. So you get 3 inches on each side. A different offset wheel (A Cayman wheel) would probably fit with no spacers under a narrow bodied car. For a flared car, just use a wheel with the correct offset.

The shock towers on the rear of a 914 lean forward, but the Cayman ones stand straight up (at least in the front/back reference plane). So you would have to remove the current shock towers and replace them with the ones from the Cayman chassis. The mounts points on the chassis would have to be removed from the Cayman donor, and welded in the correct location on the 914. The trailing arm mounts would have to be completely removed, and the mount for the front link added. From pictures, it looks like it would come out right where the trailing arm mounts are located, so maybe that could be salvaged. You would also need custom park brake cables, but those are not a big issue to get made.

If I did this, my car would have an advantage. I just remove the custom trans mount and support the trans with a jack stand. Then bolt the factory Cayman trans mounts to the trans, and bolt the other ends to the Cayman subframes. So now I would have references for the proper location of the chassis mounts.

It's a lot of chassis mods for something of unknown gains. How would it work with a stock 914 front suspension?? Would I need to go to coilovers and an RSR style suspension in the front to take advantage of it?

I have been thinking about this for years. For some reason, it intrigues me. But I think I am going to keep the stock 914 rear suspension for now. I have other things on my car I would like to finish before I even consider something of this magnitude.


Clay

Posted by: 914forme Feb 6 2021, 02:06 PM

Pete, PM sent.

Posted by: Dave_Darling Feb 6 2021, 03:01 PM

You forgot the underscore in my user name, so I didn't get the notification.

Anyway, I do not remember who made the arms. I think it was on Porschephiles back in the 90s, and what I remember is:
- They made tubular trailing arms, not blade-style
- Adjustment was out at the wheel end
- They didn't sell, and were abandoned
- It was done at least a few years before I heard about them, so possibly in the 80s

That's it. Sorry I don't have any more information.


I'd be worried about the strength of blade-style arms. There's a lot of torsion going through the 914 arm, and a flat piece of metal will bend a lot in torsion. Multiple blades can deal with that to some extent, or a blade to carry the loads in one direction with an I-beam or a box to carry the rest. (Note that the 911 spring plate for the most part only carries the torsion bar loads. The cast arm carries the twisting loads and such.)

Sounds like this is a lot of work for little benefit, frankly.

--DD

Posted by: Chris914n6 Feb 6 2021, 05:09 PM

Cayman/Boxster/996 wheels are only offset an additional inch, none of that will work as you think.

You need to narrow the subframe, which likely means fabbing a new steel frame which holds the susp arms, which would be built to fit the 914.

Posted by: horizontally-opposed Feb 8 2021, 02:54 PM

Sorry for forgetting the underscore, Dave!

Thanks for sharing what you remember. I had the sense the trailing arm project you mentioned was more recent and failed to find buyers. I suspect the market is quite different 30-40 years later—consider the number of six-figure 914 projects in recent years, or upgrades to four-piston calipers and/or 911-style e-brakes. This thread already has 3,100 views, so it would seem there's at least some interest.

As to work and cost, a pair of brand new arms that allow use of factory parts that didn't exist in the 1980s or early 1990s might end up less expensive than restoring and modifying 50yo trailing arms. People are already doing a lot of work for little benefit, building trailing arm jigs to reinforce, add 911 e-brakes, change the caliper mounts, and/or narrow 50yo trailing arms. Sounds like there are quite a few of those jigs out there, with most presumably built for just two arms. One friend suggests "about a day" to build the jigs, and one has to hope the arms used to build them aren't bent 45-50 years later. Going rate for the work above sounds like $800-2400, without making jigs.

So the critical question seems to be: Can a simple multi-blade, blade/rod, or even partially boxed arm that works with existing 914 bushings up front and mounts a modified or unmodified 986 wheel carrier at the back be engineered? That's well past my pay grade, but solving the torsional loads seems do-able. The result would leave 914 owners with long-term parts availability and choices (stock rubber, poly, or needle bearings, not to mention used or new 986 brakes, wheel bearings, e-brake parts, etc). Added clearance for a 215 or 225 rear tire with less pulling on the outer fender would be a nice upside for those who don't want M471 flares or don't want to spend $5,000-20,000 extra to put M471 flares on a "mild" six conversion with ~200 hp. Multiple lower mounting points for the rear damper might be interesting, as fine adjustment for ride height as seen on Rennline's steel 911 spring plates for $250/pair would be.

And even if steel is the obvious choice for new trailing arms due to cost, killing any weight advantage, lighter 986 calipers and an e-brake design that makes use of the interior of the brake "hat" would offer significant advantages. A two-piece rotor with an aluminum hat would take that savings even further.

Posted by: ClayPerrine Feb 8 2021, 03:00 PM

Pete...

Modding the trailing arms for wider tires won't help when the trailing arm is at the same relative location as the inner fender wall.


Clay

Posted by: horizontally-opposed Feb 8 2021, 04:31 PM

Maybe. When I did the test fit with a 215/60 on a 7R, the brake line was the only point of interference. Relocating the hard line alone might would help, particularly as the outer fender is pulled and the 15x7R is spaced out (and the less the better), but I got the sense the arm will also need to be narrowed at least a few millimeters so the tire can move around—and likely even more so with a 225/50.

While the ability to more easily sneak a 215 or 225 into stock-ish rear fenders is an upside that may or may not justify a new trailing arm for some, the far more compelling upside is no longer having to fuse 911 wheel carriers/e-brakes/caliper mounts/etc to 50yo trailing arms. I've seen that go wrong, to the point it had to be done over, even with a good shop doing the work. New arms + 986 carriers may be cheaper, as well. Any further advantages—adjustability, weight, off-the-shelf availability, etc—would be just that.

I can see a market for a good alternative to modded/restored trailing arms, no matter what sort of 914 hot rod someone is building—mild or wild. I have a tougher time seeing much a market for a setup that requires new pickup points, cutting the chassis, welding, etc. or anything else that isn't reversible.

Posted by: Chris914n6 Feb 8 2021, 08:47 PM

FYI
Boxsters use 914 rear bearings, thus the compatibility I inferenced.
911 e-brakes bolt on with a welded on tab to secure the shoes. Not complicated.

The wheel well is like 10" deep. If you are hitting arm before inner you have a camber issue.

I think you are focused on a problem only you have because you want to run 80s 911/944 spec (and 80s tech) balloon tires.
15" tires are what was made at the time. 16s were new and pricey. Today 18s are stock on just about everything.

Posted by: horizontally-opposed Feb 9 2021, 09:51 AM

Camber is within spec; it was set when the PMB arms went in and more recently checked again.

The section width for Avon and Pirelli 215/60R15 tires is listed at 8.7-8.8", while a 225/50R16 Michelin Pilot Sport 4S is listed at 9", so I'd be thrilled if there was something like 10" to play with. My test fit suggested it's closer to 9".

Adding 911 e-brakes doesn't concern me, but I've seen complications with adding tabs for 911 calipers that led to brake squeal. The remedy was a do-over. Having watched a friend deal with that after a good shop got it wrong, that is a consideration. 986 wheel carriers would eliminate that issue and make 986 four-piston Brembo calipers and drum-type parking brakes a bolt-on upgrade for a fraction of the price of 911 brakes plus 911 e-brakes, spot calipers, or RSR clamps. And unlike most caliper upgrades for the 914, which are 911 or 930 parts, 986 f/r calipers were sized and balanced for a mid-engined car. It's an idea worth exploring imo.





215/60R15
Avon CR6ZZ (vintage race/road rally available in three compounds)
Pirelli P6000 (N-spec summer)
Pirelli CN36 (N-spec w/period looks & modern technology)

215/55R15
Michelin TB 15 VHC Racing Tyre (Dry / Wet, road legal)

225/50R15
Pirelli P-Zero Trofeo R (R compound/summer)
Pirelli P Zero Asimmetrico (summer performance)
Pirelli Cinturato P7 N4 (period correct summer in modern construction/compound)
Toyo RA1 (R-compound track-day tire, retro looks)
Toyo R888R (R-compound track-day tire)
Yokohama Advan A052 (Extreme Performance Summer)

225/50R16
Michelin Pilot Sport 4 (Ultra-High Performance summer, O.E. 991/992)
Michelin Pilot Sport A/S (Ultra high-performance All-Season)
Pirelli Cinturato P7 N4 (High Performance Summer)
Pirelli P-Zero Trofeo (ultra high performance Summer)
Bridgestone Potenza S007A (Extreme Performance Summer)
Bridgestone Potenza RE-71R (Ultra high performance Summer)
Continental ExtremeContact Sport (Ultra High Performance)
Toyo Proxes RA1 (R compound track day/race tire)
Yokohama Advan Neova AD08 R (ultra-high performance summer)
Yokohama Advan A052 (Extreme Performance Summer)

Many/most of these are at the cutting edge of current tire tech, and some allow staggered sizing with 185, 195, or 205 fronts—and there are other summer tires, all-seasons, and near slicks not listed here.

So this is less about "80s balloon tires" or the idea I'm alone in wanting more tire without big flares—as others have snuck 215s or 225s into narrow 914s to varying degrees of success or failure. This is about charting a path that isn't going it alone and doesn't leave other 914 owners to do so. The keys to minimizing work on the outer fender (and all the ills it brings) appear to be wheel offset (15x7R or custom 16x7~) and inner fender/trailing arm clearance. My goal was to stoke discussion around a sensible, repeatable path to the best tires and brakes that will fit under a narrow 914 with the prospect of long availability for consumables. And maybe a trailing arm that offers benefits to any modified 914, including one with big flares.

"All" that's missing is an arm between the 914's pickup points and a pair of (modified?) 986 carriers. Can such an arm be reasonably engineered? I don't know, but I think it's a fair question to ask in a 914 forum…

Posted by: rick 918-S Feb 9 2021, 11:06 AM

Some of us really dig the look of fat vintage rubber. The trick is to stuff it into the wheel wells without having to pull the quarters. Or pulling them just enough to gain clearance. I like the narrow cars. I have a couple in storage that I hope to revive with the retro track day look. KISS.

Posted by: rick 918-S Feb 9 2021, 11:07 AM

Some of us really dig the look of fat vintage rubber. The trick is to stuff it into the wheel wells without having to pull the quarters. Or pulling them just enough to gain clearance. I like the narrow cars. I have a couple in storage that I hope to revive with the retro track day look. KISS.

Posted by: horizontally-opposed Feb 12 2021, 02:36 PM

Yeah, there's the aesthetics too. I ran 205/55R15s for a long time but have come to like the look of period correct enough performance tires on narrow and M471 cars. If space and budget permitted it, I'd probably have one of each, but I just have one, so I need to make the best of what I've got.

Chris' snark prompted me to take a fresh look at what's available, and I am actually shocked how many great 15- and 16-inch performance tires are available in 215 and 225 widths right now. Things have really changed in this regard.

Posted by: live free & drive Feb 12 2021, 06:28 PM

You can see the tire rubbing on the inner wheelhouse in the pic below, but it does not look like it hits the trailing arm.




Maybe it's set up with a lot of negative camber and hitting the bump stop Hard?

Posted by: live free & drive Feb 12 2021, 06:33 PM

If you are willing to use 6" or 7" x 16" Fuchs the tires below are very close to the original diameter at 24.8" and I bet will give good performance too:

https://www.tirerack.com/tires/tires.jsp?tireMake=Yokohama&tireModel=A-008P&sidewall=Blackwall&partnum=055WR6A008PN0&tab=Sizes

Posted by: horizontally-opposed Feb 12 2021, 06:36 PM

Saw that, and had same thought. My 914 did the same thing to its inner fenders with 205/60R15 Yokohama A-008R TU R-compound "balloons" back in the 1990s, but less aggressively. Had too much negative camber, something I fixed shortly thereafter. Never had inner fender issues again.

With the camber within spec, the first point of contact for a 215/60 on a 15x7R is the brake line on trailing arm. Relocating the line is easy enough; getting a bit more space there for a 215 is the trick. A 225 would presumably need that much more space at the arm, and would love the option to run either.



Very cool that the A-008P (with P being for Porsche) is available again, but want to stay on 15s.

Hoping Yokohama might add 225/50R16 for 911 fitments, and then the 195/65R15 & 215/60R15 A-008P that was long available. Had a set of 205/60R15 A-008R TUs and some of the very last 195/65R15 A-008P. Both were great for the street—so long as it was dry out.

Car on the A-008P from years ago seen below, on the day after Rennsport Reunion IV, I think—so 2011. My my, time flies…


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Posted by: rick 918-S Feb 12 2021, 07:57 PM

Love those tires
Hoping they come back with 255/50/16's

July 2007 WCR

Posted by: sixnotfour Feb 12 2021, 08:10 PM

Fuch it and go 17s with a deep six lip look..This Kid likes em..
rub marks are from 7x15 Fuchs, 205x15


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Posted by: rgalla9146 Feb 12 2021, 08:25 PM

That's 2" over the line.......my favorite T shirt


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Posted by: horizontally-opposed Feb 12 2021, 09:28 PM

Lol!

Rory, the principled man.

Posted by: Chris914n6 Feb 12 2021, 09:35 PM

My snark comes from experience

Your 215/60-15 are the only tires I call balloons. I even have a 225/60 but that pic might get you too excited

A few more pics and I'll post why.

Posted by: Dave_Darling Feb 12 2021, 09:47 PM

I agree that the market is very different today from what it was in the 80s and 90s. Back then, the only thing that mattered to most 914 owners was the price. If it wasn't cheap, they weren't buying it. Now, quite a few 914s are in the hands of people who are much more willing to spend money on them.

I don't know what kind of market there would be for aftermarket trailing arms, though. Might be an interesting project for someone, but I suspect that not enough people have run into problems with the 50-year-old steel parts to make that much of one, but my crystal ball doesn't work for crap! (I was absolutely certain that the Cayenne would never sell, for one thing.)

They would be neat, but they might wind up a one-off kind of thing.

--DD

Posted by: horizontally-opposed Feb 12 2021, 09:47 PM

Ha, 225/60 just a bit too F-150.

215/60 no more "ballooney" than 185/70 or 195/65—matched O.D./sidewall height and was standard on the rear of RS 2.7, RS 3.0, early 930, SC, 3.2, etc. Also look pretty fantastic on the back of a 914…


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Posted by: rgalla9146 Feb 12 2021, 10:32 PM

The wheel /tire combo most sixes actually left the factory with. A rare sight now.


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Posted by: sixnotfour Feb 13 2021, 08:08 AM

well 7.5 x 16s ..No flares,, If you have flares 245/50 x15 on 9s



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Posted by: rgalla9146 Feb 13 2021, 09:22 AM

Mmmmmmmm....the Jon Lowe GT

Posted by: horizontally-opposed Feb 13 2021, 11:40 AM

^ Fully agreed.




I don't, either, and not sure anyone does.

But looking at my options—rebuild another set of 50yo steel trailing arms for $1000-2400 for a bunch of custom work that others have done, too—got me to thinking there must be a better way.

Carbon-fiber/titanium/Elephant Racing NASA spring plate/etc are overkill. Steel seems like a better idea, and Rennline's pair of height-adjust spring plates for the 911 for $250 (!) seem more down the right road. "Simply" lenghten, triangulate, and add way to mount 986 carrier with caliper ears & e-brake and it might be something pretty attractive—for any 914 owner who puts performance ahead of originality.

Goals:

• At least as strong as factory arms
• Sacrificial to protect the unibody in event of an impact?
• Option to replicate or exceed strength of reinforced arms?
• Two lower mounting points for dampers for lowered cars?
• Fine ride-height adjust for corner balancing?
• Fine adjust for toe and/or camber?
• Save weight if possible while keeping price below cost of rebuilt/modified arms
• Provide more room for 215 or 225 tire on 15x7R wheel or custom (or 951) 16x7s

Not sure steel arms would save much weight, but alloy 986 carriers and alloy calipers might. Engineering the arm is way above my pay grade. Needs someone who understands the 914 suspension geometry well, torsional loads, etc.

Posted by: horizontally-opposed Feb 13 2021, 11:42 AM

I wonder how many 914-6s are still running 110hp to preserve the 911's place in the lineup—or U.S. ride height and 165R15s, for that matter!

They've got to be few and far between.



Love a narrow 914 with its fenders stuffed full of tire…and a GT/M471 car done right. Both of these sure qualify…

Posted by: Mueller Feb 13 2021, 01:31 PM

Boxster carriers with 15x7 BBS wheels...they almost[i] fit. I am sure with 16" and larger no problem.



Clearance with my 23.3mm(?) offset BBS wheels with 205/55-15s
I had borrowed a fixture to with the intent to modify the trailing arm by moving the tire mounting face inboard 1". I am glad I did not perform this as now the inside of the wheel/tire would for sure hit the inboard trunk wall.

Posted by: horizontally-opposed Feb 13 2021, 03:57 PM

^ Thank you for this, Mike!

Real-world test fit just as I learned something I never knew: 15-inch wheels were actually considered as standard equipment for the cost-cutting 986 but finally ruled out because they looked way too small no matter how cheap they were.

From your pic, it looks like the caliper is an issue, and maybe the 986 "pinch" strut mount too? Was thinking the latter was going to have to be modified or removed, but interesting to see the rear caliper that tight to the wheel—as 986 2.5 calipers fit inside of a 15-inch Fuchs with various custom mounts out there. If the caliper is positioned as on a stock 914 or 986, the e-brake cable is going the right way and might even be set up to hook right up with a 914. "Steering" knuckle at the back could be used for mounting to a steel arm and/or for fine toe adjustment.

Will see if I can figure out how far I spaced the 15x7R Fuchs when I test-fit the 215/60, as that may help with clearance. It was a fair bit.

EDIT: Just noticed the 987 part number. If I remember right, PAG beefed up the Brembo castings for the 986 to incorporate larger rear wheel bearings around the same time or just after the 3.2-liter Boxster S came out (1999 for 2000 MY). I wonder if that would have had any effect on the castings' outer dimensions? In this case, it might matter…

Posted by: Chris914n6 Feb 24 2021, 02:59 PM

Too much bad weather last week but did score a Boxster susp yesterday

I'll post up my findings as I get to play with it.

Posted by: douglastic Feb 24 2021, 03:14 PM

Sweet.
Still rocking the 80s 2-door Pathfinder.

Posted by: Chris914n6 Feb 24 2021, 03:15 PM

Ignore this... wrong axle

Posted by: horizontally-opposed Feb 24 2021, 03:26 PM

Ah, thanks for reporting back!

Hopes dashed with #3 for those who want to stick with 15s, as a fairly thick spacer is a given with 911R (or similar) rear wheels. So what allows use of 986 calipers with 15s on a 914 trailing arm? Smaller rotor diameter/closer mounting? as a fairly thick spacer is a given with 911R (or similar) rear wheels.

Posted by: mepstein Feb 24 2021, 03:30 PM

I’ve put lots of 15’s on cars with Boxster calipers. SirAndy has Boxster calipers f&r with 15x7 cookies.

They have to be regular Boxster calipers and not Boxster S calipers.

Posted by: eeyore Feb 24 2021, 03:30 PM

Custom 15s do fit on the 5 speed 2.7 986s and earlier. Carl V down in San Diego ran them back in the 'Oughties.

(Wasn't a custom wheel part of the plan?)

Posted by: horizontally-opposed Feb 24 2021, 03:44 PM

914-6 brakes

DISC SIZE FRONT 11.12 in/282 mm
DISC SIZE REAR 11.26 in/286 mm

986 brakes

DISC SIZE FRONT 11.73 in/298 mm x 0.94 in/24 mm (vented)
DISC SIZE REAR 11.50 in/292 mm x .79 in/20 mm (vented)

A quarter inch can be a pesky thing…

Posted by: horizontally-opposed Feb 24 2021, 06:54 PM

Yeah, potentially—but a custom wheel being:

> 15x7R (factory 911R wheel but $$$$)
> Weidman 15x7R (modified deep 6, attainable)
> Group 4 15x7R ($550 new)

Question is how much spacer, and even then if it would work. Guessing what is a tight fit with a 911/914-sized rotor and may be a no-go with a 986 rotor.

Posted by: mepstein Feb 24 2021, 06:58 PM

You use Carrera rotors for the Boxster caliper conversions.

Posted by: horizontally-opposed Feb 24 2021, 07:07 PM

^ Yes, and now looking at the 986 rotor sizes I can see why VCI (and others) question 986 caliper upgrades for not dealing with the heat-sink element in the way a 930 setup does—though a 930 setup is a very expensive proposition these days and I suspect 986 calipers are hard to beat for weight, stiffness, cost, and pad pressure spread across four pistons instead of two.

Posted by: SirAndy Feb 24 2021, 07:17 PM

Posted by: SirAndy Feb 24 2021, 07:21 PM

I ran 930 brakes before i switched to the Boxster calipers. The 930 brakes never worked as well as they should, the Boxster brakes are *much* better.

Btw. i had to machine the RJ adapters slightly to use the vented rotors i had, which are slightly wider and the calipers otherwise would not be centered over the rotors.


PS: I still have the 930 calipers in a box somewhere, if anyone wants a set

Posted by: mlmgm Feb 24 2021, 07:26 PM

Tuthill has some interesting calipers and probably could advise on adaptation to a 914 trailing arm.


https://www.tuthillporsche.com/product/tuthill-porsche-billet-brake-caliper-set/

Posted by: mepstein Feb 24 2021, 08:01 PM

The 930 is a heavy car. I think they are really close to 3K so I could see the need for big brakes at the track. The Boxster brakes and Carrera rotors are total overkill for our cars. Not that I have a problem with it.

Porsche put S front and M rear calipers on the early turbos.

Posted by: Chris914n6 Feb 24 2021, 08:28 PM

Steel bolts in aluminum parts equals stupid 4 hour disassemble times.

GOOD NEWS!!!!

15" fake Fuchs fit the stock rear by a pinky tip. Important to know that the thickness of the spacer is also the caliper to spoke clearance. No spacer = scratched caliper.





Weight whole ~ 25.5 lbs. Weight with the mount on the ground ~ 23 lbs.





More to come

Posted by: horizontally-opposed Feb 24 2021, 11:07 PM

Yep, there are a lot of cars out there with 986 calipers under 15s—so we know they'll work up front with 911 rotors. The question is whether 15s will go over a 986 rear rotor that's 0.25~ inch larger in diameter and a caliper that's presumably moved out similarly.

Looks like it might.

Chris, I wish I had measured how many washers I put in there during the test fit (will scrounge around to see if I did), but it seems that 10mm to 22mm spacers are commonly used to take advantage of the 911R's offset to get a lot of tire into narrow-body 911s and 914s. So if it's only scratching the caliper without a spacer, that might be fine. Wish I lived closer to stop by with a 15x6 "deep six," and that I still had a loose 911R 15x7 or two. Aftermarket 15s are a whole other kettle of fish.

Nonetheless, very interesting, and that many parts bolted to the carrier comes up lighter than I would have expected…

Posted by: ClayPerrine Feb 25 2021, 08:25 AM

Really.. "Total Overkill"....

I have Boxster brakes and they are not big enough for my car.

Posted by: horizontally-opposed Feb 25 2021, 08:43 AM

Hey 4.0/Vonnen man—you're just in time to do some dreaming. Cuz' if we're gonna do some dreaming…

The hot setup would be ceramic-composite rotors that work with 986 calipers. Suspect they would not only be enough for higher-power cars, but would also delete a huge amount of unsprung weight and…90-95% of the brake dust too. Downside is the usual one, though it's a lot less than the $20-30k+ seen with a set of PCCB rotors after the fact. And once you've tried PCCB, it's hard to go back. Initial bite is fabulous, and say goodbye to fade forever. Poking around, it looks like there's a vendor who can supply them for $6-8k a set depending on the size of the order. I believe they're unlike PCCB in that they aren't a mere skin—so they can be redone. If they ever need to be…

Other downside is they may need to be closer to 11.75~ inches in diameter. Their smallest diameter currently is 12 inches or just under. Questions around how much smaller they can get did come up, and it's gonna to matter with 15s.

Otherwise, you probably need 930 brakes for that 4.0. And they be heavy and costly too. Now add the cost of replacement rotors and pads from time to time…

Posted by: ClayPerrine Feb 25 2021, 09:07 AM

I have 991 C4S calipers for the fronts that were rebuilt by PMB. I am moving the front Boxster calipers to the rear, after they get rebuilt and powedercoated to match the fronts. I have not installed the fronts yet. Still looking for the right pads.

Posted by: horizontally-opposed Feb 25 2021, 09:29 AM

Guessing 16s…at least?

What rotors?

I mildly despise some of Porsche's more recent calipers, as many of them require caliper removal for pad changes. I get the argument for stiffer calipers, but when customers are creating stud kits to avoid damaging aluminum threads in the uprights during regular pad changes with track use, I have to question the logic. Fine (ish) for a street car, not so fine for a track day car.

Your 4.0-liter aside (!), I have to think 986 2.5 calipers front and rear on old-fashioned Carrera rotors are an excellent setup for the majority of hot rod 914s. Light, modern, and more than sufficient to slow 2,900-3,200+ Boxsters with 200-225+ hp on back roads where I pounded them again and again without running into fade. They held up where a 385-hp 996 GT3 on iron rotors eventually began to get pretty smelly—a precursor to fade. Two 996 GT2s with 456 hp, far more torque, and PCCB didn't bat an eye.

Posted by: Mark Henry Feb 25 2021, 10:07 AM

I'd really like to know if a 17x7 ET23 would fit on a narrow body?

This guy on the bird has a GB coming up on Maxilite fuchs that are the nicest repops I've seen.

http://forums.pelicanparts.com/porsche-911-technical-forum/1056762-17-maxilite-fuchs-replicas.html

Posted by: SirAndy Feb 25 2021, 11:00 AM

http://www.914world.com/bbs2/index.php?showtopic=170890

As mentioned above, i had to machine the RJ adapters to center the calipers over the 24mm Carrera vented rotors. That's plenty of rotor to stop a 914.

Posted by: horizontally-opposed Feb 25 2021, 11:30 AM

^ Fully agree.

(Unless it's got something truly wild in the engine bay. Like a twin-turbo V8. )

Posted by: mepstein Feb 25 2021, 12:32 PM

HP has no bearing on braking. Only mass and velocity.

Posted by: horizontally-opposed Feb 25 2021, 12:36 PM

Horsepower/torque has a big bearing on velocity…



I've learned this over and over in testing. A prime example was the 991.2 Carrera line cars, which left each corner and arrived at the next a whole lot faster than their NA predecessors. Brake fade was an obvious weak point on a closed rally stage at the press launch in Tenerife.

Posted by: ClayPerrine Feb 25 2021, 12:41 PM

Agreed.. but extreme power to weight ratios can result in an extremely high velocity in a short period of time. So bigger brakes are a requirement to shed that aforementioned velocity in an equally short time.

Posted by: Chris914n6 Feb 25 2021, 12:47 PM

Brakes are a function of weight, not HP. People upgrade brakes with HP because they tend to drive more aggressive and push the fade limits or have stickier tires that can handle the forces.
Basically, match the brakes to the weight + tires + driver.

A narrow body 914 doesn't need Box calipers, but they are an improvement in so many other ways that it makes sense.

Posted by: horizontally-opposed Feb 25 2021, 12:55 PM

^ This. And very well stated.

Reached out to an engineer with an impressive CV and a deep working knowledge of the 914 re: engineering a trailing arm that could link a 986 carrier to the 914's pickup point.

The 986 carrier idea may ultimately be compatible with 16-inch wheels and above (which makes it useless to me), but I'm curious to see what he says.

Posted by: stownsen914 Feb 25 2021, 08:29 PM

But HP has a little something to do with what velocity your car will attain . So I'd argue more hp can use more brakes.

Posted by: horizontally-opposed Mar 1 2021, 02:01 PM

...

Posted by: horizontally-opposed Mar 1 2021, 02:01 PM

Unsurprisingly, the engineer I checked with said modding a pair of 914 trailing arms made more sense than engineering > tooling > manufacturing new arms. Which is, of course, is 1,000% correct based on the economics of a one-off project.

I still think there's a (small) market for a better solution for the 914, given:

1) The number of improved spring plate options available for 911s (yes, a lot more cars, but I doubt any of the offerings are made in four-figure batches, as the % of 911 owners interested in tossing their stock arms probably isn't huge. Also, consider the production numbers: Porsche built its 1,000,000th 911 in 2017, but a lot of those 911s are water-cooled; now consider that 115,000+ 914s were built over seven years).

2) Eric Shea's ultimate five-lug conversion thread—which really should be a Classic—has 63,000 views since 2010 while this thread has 5,000+ views since…January 26 (even if one accounts for the peanut gallery/trainwreck aspect)

Posted by: SirAndy Mar 1 2021, 03:16 PM

It is and has been for many years

Posted by: horizontally-opposed Mar 1 2021, 03:29 PM

Ah, apologies.

Posted by: Chris914n6 Mar 12 2021, 09:27 PM

Stock rear fender and why some tires don't fit well. Just over 9" of total tire space.

Driver side:
https://flic.kr/p/2kKpy1j

https://flic.kr/p/2kKpxVj

Pass side:
https://flic.kr/p/2kKq58V

https://flic.kr/p/2kKkPvN

Posted by: Chris914n6 Mar 12 2021, 09:46 PM

My Boxster wheels. 7x16 225/50, 9" wide at sidewalls, no spacers, et40. No contact on inner sheet metal. Rolled fenders for plenty of room & adjustment. I usually run a 15mm spacer making it et25.

9mm less offset than the 911R wheels.

https://flic.kr/p/2kKpxHL

https://flic.kr/p/2kKpxD7

Fuchs reps 7x15 225/50, 9" wide at sidewall, et23. (9.5" wide at sidewall for 8x15 225/50). The 8x15 didn't fit under my fenders as the extra 1" is on the outside (same backspacing as 7x15)

https://flic.kr/p/2kKpyP3

https://flic.kr/p/2kKkQmv

Posted by: horizontally-opposed Mar 12 2021, 09:54 PM

^ Yep, which explains why I was able to get a 215/60R15 on a 15x7R into both fenders with the car back on its weight.

Both the Avon CR6ZZ and Pirelli P6000 list a section width of 8.8 inches when mounted on a 7-inch wheel. But that tire is gonna need a little more room to "walk around" under load and with the suspension under compression. Question is how much? Or, rather, how much more than 0.2 inch? Someone mentioned 5mm per side is enough (so 10mm total, or .39-inch), but I'm guessing it'll need to be more than that?

Michelin lists the new Pilot A/S 4 225/50R16 with a section width of 9 inches on a 7-inch wheel, which is closer than the 215/60R15 than I would have thought. Toyo RA1 and Pirelli Trofeo R list a section width of 9.2 inches. Yoko Advan A052 lists a section width of 9.1 inches on a 7-inch wheel—so the 225/50R16s would require a bigger stretch…but these are all great tires (as anyone who has tried the A/S 3 knows…and the rest are R-compound wonders).

I guess the question for those who have pulled rear fenders is: How much room have you snuck in back there without paint work? I am guessing not much…

Posted by: Chris914n6 Mar 12 2021, 11:15 PM

Problem is at 9" you are either going to have to be exact with the offset or flexible with the camber.

Also the camber will change with susp travel so don't be surprised if it rubs the inside on bumps.

I got another 1/2" or so and didn't try to save the paint, which fractured off.