I believe, if I’m not mistaken, there was a 13mm front sway bar for the 912 cars.. and I was wondering if that wouldn’t be more appropriate for a 1.7L 914 rather than the stock oem 15mm. I’m not sure if anyone bothers with a ARB on a 1.7L, but the 13mm ones are fairly easy to come by, cause everyone upgrades to bigger. So that’s a plus. Thoughts?


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porsche thought they were.
and fitted them to just about all the 74 1.8s after they got full control of the project.
i'd have to look up whats in mine, but its standard out of the box since new.
front and rear sway bars. 74 1.8.

i ain't got no complaints. its sweet.

Factory set it up for the best possible all round driving. Why mess with it? Reproduction 15 mm bars are now available.

The 13mm will be a lot better than no bar.

Anti roll bar size has nothing to do with engine size given that for all practical purposes all T4 engines are the same weight and don't fundamentally change the weight distribution of the vehicle.

I see a lot of discusion about adding front bars but almost no one is stating why they want one, what problem they are trying to solve, and what their current setup (spring rates f/r, presense of rear bar & what size, tires, etc.) are.

FWIW - as a generalization, adding a front bar will increase understeer, adding a rear bar will increase oversteer. So how many are really trying to increase understeer?

To the point above, a 13mm bar very well may be better than a 15mm bar if you don't have a rear bar as part of the system.

Again, all depends on what problem is trying to be solved.

Highly recommended reading
Click to view attachment

Ive done at least one 13mm Front/No Rear update with some 140# springs I though it handled pretty damn good.

Yea, heavier rear springs can serve as a bit of a substitute for no rear sway bar. Like superhawk996 has said in the past, suspension is a combination of parts but the front ARB and stiffer rear springs is a great fix over stock.

I'm going to just a little more.

The discussion around Anti-Roll Bars (ARB) that presumes less body roll is an indicator of better handling. That is a generalization that does not hold in all circumstances.

I have seen instrumented handling data on vehicles that shows that they have less body roll than a benchmark competitor that is perceived to handle better, yet the competitor has MORE body roll. Keep in mind, this is as measured with precision instrumentation, not just some seat of the pants perception of body roll.

Likewise, I've seen objective test data on cars that handle BETTER than a compeititor that that has less body roll.

Food for thought. Need to understand what the end objective is.

Indeed, it's becase the 140# rear springs add to the rear roll stiffness. However, the stiffer springs come with a ride harsness penalty. Using a rear ARB with softer springs would yield the same hadling result without the ride degradation.

As stated, the suspension is a system. Nothing can be changed indepently without affecting something else.

Here's a fun fact. A race car may often be purpose built around a specific (spec) tire. All aspects of the suspension deign are tweaked to give that tire exactly what it wants. Sometimes that is more weight transfer, sometimes it is more camber, and so on. But the bottom line is the rest of the suspension is optimized to give the tire what it wants since the tire is the interface to the road and ultimately determines handling.

So how would you know what the tire wants? Via lab testing of the tires. Tires can be characerized on flat track machines to determine where they perform best. What is the normal load that gives the highest grip? How does the tire respond to the rate at which normal load is transfered to it? Characterization of slip angles vs. load, caster, camber, toe, temperature, on & on.

Superhawk, I based my question on (my) understanding that a front bar is basically there to add a bit of understeer which helps counteract the oversteer situation of a given car.. I certainly may have that all wrong, I’m no suspension expert (& thanks for the book recommendation). But if that’s close to being right, then in my mind a smaller bar would be more appropriate for a simple 1.7L street car than the 15mm one used with a 2.0-2.4L type IV power plant (for example - since they weigh the same) - because 1.7L would theoretically produce less oversteer (all other things being equal).

Anyway the car will get a bar while torn down for bodywork, and the 13mm seems logical enough to me, I’ll probably give it a try. BTW, did any of the 1.7L cars come from the factory with sway bars?

Also, @wonkipop (thanks for your input) says the 13mm bars are on all 1.8L cars, but I don’t recall reading that 914-4 used anything but 15mm - perhaps that was a European/Aussie thing? Anyone?

I wonder what Porsche’s thinking was with giving the 912 a 13mm front bar, it being a more tail happy car than a 914.. but the 914-4 getting a 15mm up front?


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Let's untangle the powertrain aspect.

There is steady state and transient handling. Both matter but generally we attack steady state 1st when tuning. Think of steady state as the skid pad. Big circle, constant turn radius. Does the vehicle track the circle naturally and linearly with respect to steering wheel input?

I think you're alluding to power on oversteer - a transient condition. Otherwise engine doesn't matter. Power on oversteer really isn't going to get addressed by bar other than to the extent that rear roll stiffness (and to a degree front) can help keep the rear wheels planted preventing a loss of lateral grip as the rear tire with the least grip (usually inside) spins up under power. This is a bit of red herring since an open differential tends to do the one wheel peel on the inside, lightly loaded tire. This isn't where the majority of the lateral grip is anyway - it's on the outside tire due to weight transfer. Now, let's consider an extreme example; 400 HP engine. It won't matter what size rear bar you have or how much front vs. rear stiffness you have, the outside tire will break loose (on power) and the vehicle will be inclined to oversteer and/or spin.

So let's not chase bars to solve transient power on oversteer regardless of engine.

With respect to your question on the 912. If you wanted to reduce body roll on a rear engine car that already has an oversteer tendency due to its rear weight bias, you definately would not want to use a rear bar to limit body roll.

So that leaves the front as the logical place to put the ARB. So why not a massive front ARB?

Now we are back to steady state vs. transient handling.

The rear weight bias of the 912 or 911 is always there. However much good the rear weight bias does for acceleration and increased effectiveness of the rear brakes, it is a HUGE liability for transient handling. We all know about 911 lift throttle ovesteer. I've never driven a 912 but everything I've hear is that it actually oversteers less than a 911, due primarily to the lighter T4 engine.

What happens is that if the front has sufficient grip, and turns in quickly at the start of the corner, the (heavy) tail end wants to keep going straight. As the front continues to turn in, at some angle, the back of the vehicle has a sufficient moment arm (leverage) around the center of gravity and the back end begins to "swing" on its own due to that moment arm and inertia. The result is oversteer.

The front ARB helps limit the inherent oversteer to an extent, reducing that tendency for the front to turn in too quickly for the rear to follow. But again this is tranient, at the very start of the turn.

You can't put a big enough front bar on it to completely kill the inherent transient oversteer. If you try, you'll just end up with a car that doesn't want to turn it at all and which continually understeers in more gradual corners once the vehicle (yaw rate) is in a steady state condition. It would lead to a loss of steering confidence.

So not being a 912 guy, I suspect that Porsche found the 13mm to be just enough to settle the rear (during transient conditions), but not so much that it killed the liveliness of the vehicle under steady state conditions. Since I don't have experience tuning a 912, I'm open to criticism but that is the way I'd look at it from a theoretical tuning position.

Note: I should also add that Limited Slip differentials can add another whole set of variables to both transient and steady state handling but I don't want to go there since so few of us have them.

My 912 came with just the 13mm front bar. The 912/616 engines are not only 200lbs lighter, the weight isn’t as far back as a 911. Less pendulum effect.
But that will be all out the window when I convert it to a 3.2SS.
The nice thing about 914’s are they are so neutral out of the gate. No need to “fix” anything, just improve.

Wow, always a wealth of knowledge offered up so enthusiastically here on the world .. thanks for the education (everyone), I appreciate it!

Anyone know if 1.7L cars ever came with sways at all, from the factory? I doubt it, but would like to know for sure…





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The early cars did not come with sway bars though they did come with mounts on the a-arms.

Having a little roll and compression is a good thing if you are thinking about pushing the weight of the car around. In autocross it is used all the time to increase traction. If you have a powerful engine and powerful breaks you often need very stiff components, but you still get dive and roll because physics. Take those same components and put them on a car with a weak engine and 50 year old brakes, not so great for handling.

Great discussion, and I've long wondered about adding a rear ARB.

Consensus when I added a front Weltmeister ARB and 140lb rear springs in the 1990s—hard won by a super active autocross and time trial community around the 914, presumably based on lap times + handling dynamics—seemed to be:

> Weltmeister front ARB, no rear ARB
> 140lb rear springs
> Konis (red for more street, yellow for more track)
> Lowered and aligned
> Widest rubber you can fit

I followed that recipe and also thought the car handled really well, both for autocross and for back roads. But this isn't 30 years ago, and I'm here to learn!

not an aussie /uk thing.
914s never sold in australia.
my car came from maryland usa.
never modded.
out of the box with the roll bars.
standard show room stuff.

1.8 has even less horsepower than a 1.7 unless you are unlucky enough to own a 73 cal 1.7.

the 74s are interesting - as i understand it this is how porsche-audi north america decided to set the base models up to improve tham. it is during this period that porsche gained marketing control over the joint project. theoretically you could despec a 74 1.8 and get rid of the performance group package but you would have to order it that way.

to clarify - far as i know its 15 front and 16 rear.
i could try and double check that.
i didn't mean it had 13 mm sway bars.
i meant it had front and rear sway bars, not just a front one.

this is what porsche thought they should have for street.

i've driven an earlier car a quarter of a century ago without the bars.
i preferred mine.

but then again i run skinny 165 tyres so most blokes would consider me a retard.
i do run bilsteins, but that is because boges are not available in the modern world.
it runs stiffer than it used to. i'm not complaining about that. its far superior out on second rate old country roads and stays planted with the bills. but the spriings are soft and standard - and comfortable. we don't have smooth tarmac once you get off the main interstate highways in australia.

if you want the evolved set up for the base cars that porsche thought appropriate thats the set up.

but then again you could experiment.
note - they appeared to have the slightly stiffer bar on the rear,
which kind of goes with your idea of a single softer bar on the front.
but that will be more aggressive effect than the factory set up.
depends what you want to do with the car.
you can also get a lot out of setting it up level or a little bit nose down.
or as the factory did, a little (or a lot) nose up. that made them understeer.

The only real problem is that what is good for autocross isn't always what you want for the street. AX tends to favor cars that are easy to rotate at low to moderate speeds. You very well find that ability to rotate isn't appreciated on a big highway cloverleaf sweeper taken at 2x or 3x posted speed.

Don't get me wrong, we all follow the recipe to a degree. The moral of the story, don't just follow blindly, tune to what suits you and know why you're doing it.

Following that AX recipe forces some ride degration with the 140# springs that might otherwise not be needed had we opted for a softer spring and a smallish rear bar.

Don't get me wrong, I largely followed the same recipie you laid out when I got started back in the early 90's with suspension and chassis tuning and didn't fully understand the tradeoffs I was making. Not everyone want's to go to all the time, expense, and trouble to to learn how tune. That's OK as long as they know they are making tradeoffs in the process.

Can't judge bar stiffness just by diameter. Although the rear bar appears larger (by 1mm) it is a far less effective geometry than the front bar. I'm sure the overall rate of the rear bar is less than the front based on experience though I haven't done the math to calculate the rates.

The 15mm OEM front bar is basically a stright bar with two very short lever arms down to the LCA's. That aspect makes it highly effective.
However, the drop links are long, thin and probably flex substantially reducing effectiveness some.

The 16mm OEM rear bar has very long lever arms. But then the rear drop links are very short and probably don't flex much at all. But on the whole, the stiffness lost to the long lever arms won't be made up by the short, effective drop links.

Bottom line, I don't know the engineering rates (wish I did - next time I'm bored, I'll do it) but don't judge an ARB just by it's diameter.

Yes that helps, cause you had me confused and thinking 1.8L had a bar I’d never heard of being installed. Thanks again.

And just a side note, while we’re on the subject… the /6 cars apparently (and eventually) came with a 16mm at front and a 15mm at back - so opposite the stock /4 set up… I suppose that’s because of the extra weight of the engine and nothing to do with a power increase over the /4, as super hawk has explained.



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Good student

very good point. quite a different affair that rear bar.

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the sixes also have a slightly wider front track?
which makes them a bit different too?

I spent a lot of time playing around with different things when I did my 914 suspension. Mostly in IMHO this is where you should throw your money and time in the car and not so much on the engine other that have a good running one.

For street and ocasional twisties I ran Billies Sports on all four corners ''progressive" valving set up. Ajustable perches with #140 SR in the rear.

NO rear bar.

In the front the car was ever to slight biased down in the front by torsion adjustment.
Rack spacer to take out any bump steer with a solid steering coupler. Turbo tie rods and stock ball joints....all new.

I found the stock drop links length for this junk and threw them away and used Tarret adjustable links for the bar.

Corner balanced and aligned to sock specs less a little more camber in the front, that car drove like it was on rails......forget the size of the engine it had a 1.7.

I could take 911's ....downhill of course in the corners.

I ran 205's BTW for rubber all the way around not a staggered set up on stock 2.0 fuch's. The fenders were already rolled when I got the car.

Mostly I think the car didn't really need one but Porsche...and still to this day...and I know cause I normally never buy a P car that isn't optioned up makes money by selling options....my Cayman was the only exception. The car is just so fun to drive who needs Nav.

My. 02 without all the technical explanation of why.

Yeah, essentially I’m just trying to set up a little 1.7L, as a fun daily driver - thanks for sharing!


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We ran a 19mm front with a 16mm rear on our 71 1.7 which did not come with sway bars stock. They were both H&H bars. The car was a great autocrosser and track car with reasonable ride on the street. One friend in our club ran the 912 small bar in the front only and it worked fine and had a better ride on the street.

Charlie

Yep, fully agreed re: what one needs for autocross vs street (or track). While I'm a big fan of autocross, the need to rotate the car to get it to turn in at low speeds doesn't always lead to good setup—or muscle memory!—for higher speeds on road or track.

Interestingly, the "no rear anti-roll bar on a fast 914" dictum of the 1980s/1990s should make the car less prone rotate—right? Of course, 140lb springs add roll stiffness at the rear, while front spring rates were often left alone (ish). Reminds me a bit of Porsche's approach with the 987.2 Boxster Spyder: They decreased the rear ARB, but upped rear spring rates by 50%! When you think about how well a regular 987 Boxster/S handles, that's a big "tweak." But it made for the best-handling 987.2 hands down—and that's saying something because all 987s were great!

My current setup—911T front torsions bars, 140lb rear springs, 22mm front ARB, no rear ARB, rubber bushings all around—worked well when the car had 80~ hp and still works well with 200~ hp. Everyone who tries the car raves about the handling, though I know it can be a bit better/sharper still. While I followed the advice of 914 autocrossers and track-day denizens when I was a teen, curious to listen to current thinking so many years later…as I will probably do my 914's suspension and brakes one more time. <I hope!> Currently eyeing KW dampers, different ARB(s), and an LSD along with 986 calipers front and rear. Spring rates seem about right. Don't want to go higher for the street…

I do not feel it is a fair comparison between a 912 and a 914. The 912 has a torsion bar rear suspension, while the 914 has coil over shocks. Both systems have very different handling characteristics. My 76 came with both front and rear sway bars. While my 73 has zero bars. It is my understanding that most, if not all early car did not come with them.

Pete, adding LSD will make the car push coming out of corners. The primary reason for LSD is to prevent inside wheelspin while hard on throttle out of a tight corner. If no wheelspin, then why bother? The car will rotate better without one.

We all have preferences... mine is spring rate before ARB rate. Good to know about the 987.2 Boxster Spyder going with a lot more rear spring. Too bad they're crazy expensive!

All of my SWB 912 coupes came with a front bar. My 912 Targas did not.

All of my SWB and up to 73 LWB 911 coupes came with a front bar. 67 911S was first to have a rear bar. I added a rear bar to a couple of them, which made them more lively. I also removed the front bumper weights on all my SWB 911s but also ran 6" Fuchs. Lottsa fun!

Yep, felt that with Paul Sayegh's 914 3.6—though I wondered how much of that was due to his type of diff (torque-biasing, I think?), tire/outer track width, and suspension setup.

Have a lot of time in cars with and without LSD, and in a lot of situations. Depending on how they're set up, they can not only cancel inside rear wheelspin when leaving a turn, they can add supreme confidence on the brakes on the way into a turn. ARBs and other elements need to be working in concert to avoid understeer, but I've driven a lot of rear- and mid-engined cars where all elements of the suspension are doing just that—and the feeling is tremendous. And pretty rare. Getting to it adds up quickly, and the fact is a 914 (1.7 too) with nothing more than stock-ish front torsion bars, a front ARB, 140lb rear springs, good dampers, and good tires is a seriously effective car—and a ton of fun too. Probably 85-95% of the ability & fun factor for a lot less money. Maybe that's why the simple recipe for the 914 was/is so popular. All of the above can be done for roughly the price of adding an LSD.

You brought something up I hadn't really thought about: While I got crazy inside rear wheelspin in a lightly modded, 320~hp 987.1 Cayman S with an open diff on back roads years ago—to the point I finally had to turn PSM off and manage it myself, deleting a safety net that rarely intrudes otherwise—I don't think I'm getting much if any wheelspin with 200~hp in my 914. I do want to add short gears, though…

But back to the OP's question: For a 1.7, my vote is something like the old Weltmeister front ARB and no rear ARB with stock front torsion bars & 140lb rear springs on adjustable perches. Good dampers, too (Koni reds if you can find or rebuild some). Dead simple setup, simpler than mounting a rear ARB, and can be corner balanced. More than enough for most drivers and most 914s—rides nice, works for autocross, and even good enough for occasional track use. Will work well with tall sidewalls, or short ones. And ready for double the power if/when you get around to it.