Let's talk rear sway bay! Who's running with it

[Fubawu]

I have been noticing a few of the drivers running without a rear sway bar. They swear buy it and I have been convinced on more then one occasion to try it. I find the car awkward without it. Pushes and seems to have much slower turn in. What seems to be the consensus here?

This is for early 911's/ torsion bar cars.

[RichardNew]

I've always run with a rear sway bar.

There really isn't much information out there on sway bar adjustment for the 911. A lot of companies sell sway bars and then never discuss how to find the correct location.

I went back to my records from the late Carroll Smith. He was the lead guru on the GT 40 - and a lot of other cars.

"Sway bars allow us to change the understeer/oversteer balance of the car quickly and easily. If we make the rear nit-roll bar softer (either by lengthening its actuating arm or by going to a smaller diameter bar) then less load will be transferred laterally at the rear of the car."

A sway bar shouldn't have much of an effect on turn-in. I usually play with toe settings to alter the turn-in.

If you're only driving on the street the stock Porsche sway bars work just fine. If you're really really serious at the track you might use the Tarret bars.

If you have adjustable sway bars keep in mind that you can adjust yourself right out of the ballpark.



When I was running competitive events I always had someone look at my inside wheel. It's just about right in the above picture. I always wanted it less than 6-inches off the ground. It may have been a backyard technique but we won everything. There are times when your just have to drive it and forget about all the little tech stuff.

If my inside tire was on the ground - or higher than 6-inches I would adjust my bars. Keep in mind that you only adjust one end of the car at a time.

Richard Newton
Turbo Tie Rod Ends

[winders]

What torsion bars are you running front and rear and what front sway bar are you running?

Most of the time a street car really needs a rear sway bar because they are too roll stiff at the front. Even a car with 21/31 setup benefits from a rear sway bar.

[winders]

Originally Posted by RichardNew

When I was running competitive events I always had someone look at my inside wheel. It's just about right in the above picture. I always wanted it less than 6-inches off the ground.

If my inside tire was on the ground - or higher than 6-inches I would adjust my bars. Keep in mind that you only adjust one end of the car at a time

Most ridiculous way to tune ever. You tune based on how the car feels, not what it looks like.....

[Fubawu]

I'm running 23/33 torsion bars, car is track only. I can't remember off the top of my head
on sway bar sizes but I do feel like there could be a bit of binding on the trans cross member.

[winders]

Originally Posted by Fubawu

I'm running 23/33 torsion bars, car is track only. I can't remember off the top of my head
on sway bar sizes but I do feel like there could be a bit of binding on the trans cross member.

With that torsion bar setup you need a rear sway bar. Otherwise you would be tool roll stiff at the front.

[Fubawu]

Originally Posted by winders

With that torsion bar setup you need a rear sway bar. Otherwise you would be tool roll stiff at the front.

So if one was to not run a rear sway bar they would need to soften the front torsion bar?
This in turn would reduce roll stiffness in the front.

[winders]

Originally Posted by Fubawu

So if one was to not run a rear sway bar they would need to soften the front torsion bar?
This in turn would reduce roll stiffness in the front.

You would need to go with a smaller front torsion bar, yes.

[Plavan]

22/31 here with a Tarrett RSR rear swaybar. I benefit from it.

[Cory M]

The rear bar is such a useful tuning tool I can't imagine running without one. Even if you had really stiff springs, which you don't if you're on torsion bars, I think you'd still want a thin bar for the adjustability.

[Dave at Pelican Parts]

Don't forget to reinforce the rear sway bar mounts, especially if you upgrade from the stock bar to a larger one!

--DD

[winders]

Originally Posted by Cory M

The rear bar is such a useful tuning tool I can't imagine running without one. Even if you had really stiff springs, which you don't if you're on torsion bars, I think you'd still want a thin bar for the adjustability.

When my race car was on bias-ply slicks, I did not run a rear anti-roll bar. Now that I am running radials, the car seems to work better with a rear anti-roll bar. I upped the rear spring rate enough that I didn't need one, but the car just didn't behave as well as it did with a rear anti-roll bar. I think it may have been a shock valving issue as the spring rates ended up being quite a bit higher than what I had when running the bias-ply slicks.

As long as the front anti-roll bar has enough range for tuning roll couple distribution, you don't need a rear anti-roll bar.

[Charles Freeborn]

My first season of DE my car didn't have a rear bar. Car seemed squirrely, but I was a novice, so probably not the most objective view.
I've since repaired and added a rear bar and car is definitely more predictable, but my experience has gone up considerably too, so there you go...

[winders]

Originally Posted by Charles Freeborn

My first season of DE my car didn't have a rear bar. Car seemed squirrely, but I was a novice, so probably not the most objective view.
I've since repaired and added a rear bar and car is definitely more predictable, but my experience has gone up considerably too, so there you go...

What do you mean by "squirrely"?

[Driven97]

A rear sway bar and rear springs both do the same thing in a corner, but in different ways. The way the springs work is pretty straightforward, a swaybar transfers rate from the inside spring to the outside. To better visualize things, I like to think of a swaybar as a spring that only works in roll.

Let's you have two cars with identical roll rates, one with big springs and no bar, and one with soft springs and a big bar.

Compared to the big spring car, the big bar car, thanks to it's softer springs, will squat and plant better on power. Conversely, it'll pitch up the rear more under braking. It'll handle straight line chop bumps better, but since the left and right are tied together somewhat, it'll handle single wheel bumps worse. Mid corner, since it will be "pulling up" on the inside wheel to make up rate on the outside, it may also work the LSD harder to put down power or have more of a tendency to spin the inside rear in certain circumstances.

So everything is a tradeoff.

The best part about sways is their easy adjustability. In 10 minutes or less you can make a tweak or disconnect one completely, something you can't do with a set of torsion bars.

[Charles Freeborn]

Originally Posted by winders

What do you mean by "squirrely"?

I just felt like when in began to break loose it was smoother - i.e. less chatter and more predictable. Again, I think improved driving skills / more experience had much more to do with it. Other things changed too - such as different tires / wheels, etc , so there were too many variables to be able to pin it on any one thing. When and if I take the next step up in performance / handling modifications I'll switch to adjustable bars so I can begin gathering data in a more scientific way. As it stands now I still haven't reached the cars limits of cornering. Brakes, yes, cornering no. Maybe next season with another half dozen track days I'll begin to out drive the car.

[winders]

Originally Posted by winders

What do you mean by "squirrely"?

Originally Posted by Charles Freeborn

I just felt like when in began to break loose it was smoother - i.e. less chatter and more predictable. Again, I think improved driving skills / more experience had much more to do with it. Other things changed too - such as different tires / wheels, etc , so there were too many variables to be able to pin it on any one thing. When and if I take the next step up in performance / handling modifications I'll switch to adjustable bars so I can begin gathering data in a more scientific way. As it stands now I still haven't reached the cars limits of cornering. Brakes, yes, cornering no. Maybe next season with another half dozen track days I'll begin to out drive the car.

If all you changed was adding a rear anti-roll bar, the car should have felt more squirrelly since the rear would be even stiffer. But, as you point out, you changed a bunch of things including your skill level.

[Flieger]

Sometimes adding a sway bar can increase grip if the suspension was bottoming out prior to that or if the camber curve is so poor that limiting travel increases grip more than load sensitivity decreases it.

[winders]

Originally Posted by Flieger

Sometimes adding a sway bar can increase grip if the suspension was bottoming out prior to that or if the camber curve is so poor that limiting travel increases grip more than load sensitivity decreases it.

Only in exceptional situations. The camber curve on a 911 is not that bad either. In all my years autocrossing and at the track with 911s, I have never seen anyone reduce oversteer by stiffening the rear sway bar.....

[crashmy911]

Disconnect rear sway in the rain