Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? Options

[rgalla9146]

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.

[mb911]

God I am too cheap on everything I do..

[Mikey914]

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.

[Superhawk996]

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

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.
(IMG:style_emoticons/default/confused24.gif)

[barefoot]

While repairing damage to my 914's passenger rear quarter caused by a texting driver crashing into it (IMG:style_emoticons/default/mad.gif) ,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.

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.

[barefoot]

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.

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. (IMG:style_emoticons/default/biggrin.gif)

[horizontally-opposed]

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, 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.
(IMG:style_emoticons/default/confused24.gif)

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… (IMG:style_emoticons/default/biggrin.gif)

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. (IMG:style_emoticons/default/biggrin.gif) ) 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 this car. 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…

[horizontally-opposed]

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.

[horizontally-opposed]

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.

[horizontally-opposed]

From our own Keyser Sose:

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

[horizontally-opposed]

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.

[Superhawk996]

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 (IMG:style_emoticons/default/stromberg.gif) strapped to the top of sports cars. I have a long history of doing similar things.

[brant]

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.

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

[mepstein]

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.

[stownsen914]

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 ...

[horizontally-opposed]

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.

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-st...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.

[rgalla9146]

"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 ?

[horizontally-opposed]

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 ...

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…

[horizontally-opposed]

"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 ?

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

[930cabman]

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 ...

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