Sway bar adjustment--how do you systematically optimize?

[JonT]

I've had adjustable sway bars on my car for 3 years now and finally feel like its time to start adjusting them to improve handling characteristics. I have the front and rear set pretty loose. These are Weltmeister btw. Oversteer not really a problem, understeers a bit but better now with slightly more balanced sized tires. 245/45/17 front 275/40/17 rear. Car leans quite a bit--more than I'd like. How should I go about making these changes--I'd like to experiment with this now that I think I will recognize the changes after driving the car for 2 1/2 years without making any suspension changes.

[ZOA NOM]

Unless you are tracking the car, I don't think you'll really benefit from adjustments to the swaybars. If body roll is the only issue, I would suggest stiffening both front and rear the same amount, and see if the car still pushes. The safer attitude is for the car to understeer a little. Once you establish that you've reduced the body roll, then you can begin to make changes to each end independently. I would caution that tire pressures should be very consistenet throughout your adventures. IMHO, if you are driving fast enough on the street to feel the need to make swaybar adjustments, then you aren't being safe in traffic.

[Quicksilver]

The first bit to realize is that a suspension that has been fully optimized for ultimate handling is going to be more tail happy then you want for the street. Most people who are used to an understeering car have to drive a correctly balanced car for a while to get used to the need to change their driving style so it doesn't bite them when they lift.

That said, it sounds like your car is so biased to understeer that your first big improvement will be to crank up the rear bar. Ultimately to improve handling both bars would need to be adjusted stiffer but still the rear would probably be stiffened more then the front.

Obviously other then just feeling the balance and adjusting accordingly, the real solution is to get on a skidpad (a long flat constant radius corner) and start slowly changing things. Spending money on a tire pyrometer is money will spent too. (borrowing one works great too!) Learn to use it. Reading the temps isn't completely straight forward. There is no real substitute because what you are really trying to do is get the tires to do as much as possible and that is the way to do it. A great way to learn more about tire temps is to offer to read the temps for people who have well sorted cars that are pushed hard. You will find that 'real' temps have a few surprises compared to the examples shown in books.

[JonT]

Sorry forgot to mention this is for track driving. DE's. Wayne--I do have a pyrometer that I have started to use after DE sessions and will experiment with this after I find a safe skidpad to use.

[David]

I'll assume you have stock torsion bars. I'd go full stiff on the rear and near the middle in front, then make a careful lap or two knowing that you may have to catch it. If it's still understeering, go softer in front; oversteer, go stiffer in front. If you go full stiff in front and you're still oversteering (unlikely) go softer in the rear. JMHO.

[chrisp]

What size weltmeisters? If they are 22/22 I agree with full stiff rear and slightly softer front. At full stiff front and rear it oversteers too much. If you have 22F/19R then the front should be that much softer. Also keep in mind you have a targa and a 3.6 in back. It'll set up differently than an SC...which is what my comments are based on.

[jaydubya]

I agree with what has been said above, just want to add a few things:

Ideally, swaybars should be used to make small adjustments to car understeer/oversteer behavior once you have your camber and tire pressures adjusted to provide even temperatures. They should not be used as a substitute for appropriately sized torsion bars.

Steve Weiner has said that you simply cannot have too much rear roll stiffness in a 911 for track use. After upgrading my suspension again for this season and spending some time on the track with it, I completely agree. Assuming this is a track only car, you get the biggest rear torsion bars you can find. I suggest 33 mm rear. These are nicely balanced with 23 mm front. Then adjust the swaybars to give the car the balance that you want. Too much front swaybar tends to generate inside front wheel lift on corner exit, so try to keep the front swaybar on a relatively soft setting and adjust the rear to get the balance right.

Cheers,

Jeff

[JonT]

Currently 22 front/ 30 rear torsion bars. Weltmiesters are 22fr/22r. Revalved Bilsteins.

[ljowdy]

Here's what I've done. If you have an adjustable rear bar and the car understeers, stiffen the rear. This allows less rear tire roll and loosens up the back of the car and helps to eliminate understeer.

If the car oversteers then soften up the rear bar, this allows the rear tires to roll and grip increases.

Oh yeah, they're called Anti-sway bars, not sway bars

[David]

Originally posted by JonT
Currently 22 front/ 30 rear torsion bars. Weltmiesters are 22fr/22r. Revalved Bilsteins.

That's the same as my setup except I have 31mm rear bars. I'd still start with full stiff rear and mid to soft on the front bar.