Norm Swanberg

My 88 951 is near stock, with Koni gas adjustables, 1 degree negative camber, front and rear. It was neutral with 40lbs in the front tires and 42 rear, hot off the track. I am going from a 25.5 mm front sway bar to 26.8. This will give a28% increase in stiffness if I understand the math. I have had conflicting input as to what this will do to understeer. Some say it will increase others say decrease. A Porsche mechanic with racing experience and a Rennlist posting said a larger front sway bar will decrease understeer. A grid I found on the internet and one in an old Automobile Atlanta catalogue said increasing the front sway bar will increase understeer. I need to have the car neutral. I have signed up for three track days close together and will not have time for things like spring or rear bar changes if it is not neutral on the first day. I can do some adjusting with tire pressure and soften the front shocks, if necessary. I am sure there some of you that have made similar changes and know what happened. Which is right?
Thanks,
Norm

95ONE

typically. NOT always. understeer.

thingo

If the car is nuetral now, why are you adjusting the suspension?
When my car is understeering to much, I stiffen the rear sway, so I think a larger front bar will make the car tend to understeer.

gt37vgt

is 26.8 the factory big bar ? I'm sure it wont be that extreame probaly need slight goemetry change to tune it up a touch.

shiners780

Increasing the rate of the front sway bar will typically increase the cars' tendency to understeer, especially in turn entry. Making changes to the front of the car has more of an effect on handling in the first half of a turn, making changes to the rear of the car has more of an effect on handling in the last half of a turn. <Generalizations - nothing is absolute in suspension setups as there are many variables to consider.>

There are a bunch of good sources online dealing with suspension setups and how changes will affect handling. A quick google search turned up these examples:

http://www.wtrscca.org/tech.htm
http://www.kormanfastbmw.com/thandling.htm
http://importnut.net/tiretech.htm#hipochrt
http://www.cjtire.com/pdfs/Servicing...&%20Wheels.pdf

'Thingo' has a good question: If your car handles neutral now, why mess? If you like to tinker with different setups, maybe you should consider an adjustable sway bar. That way you are not locked in to any particular setting, and can make quick and easy adjustments at the track.

Norm Swanberg

Thanks for the input. The stiffer sway bar was added because the front tires were rubbing the tops of the wheel wells. The only place I heard it rub was exiting a turn. I am also going from street tires to Toyo RA-1's. This will increase the G's on corners and make the rubbing worse. The diameter of the worn street tires and the new RA-1's is the same. I also intend to add to the stops on the front shocks. I am going to plastic bushings in the insides of the front bar. The 26.8 bar came from a 968, but I believe that size was an option or was the Turbo S bar on 944's. I have already spent too much on the car/track time. I do not intend to be the fastest on the track, just have fun. I am in the intermediate groups. There will be someone driving something that I will be close to. My goal is to not have tires rub and have the car neutral. It sounds like the cheapest thing to try would be camber changes as suggested. If that is not enough the next thing would be a rear Weltmister adjustable bar.

95ONE

not exactly the best way to keep a tire from rubbing. I doubt it will fix your problem. Stock springs? Are they just cut? Bad wheel offset? Maybe something like these that needs to be looked into first?

Keithr726

Sorry to hijack but should my AC compressor be contacting my sway bar?

95ONE

That was so random I laughed out loud!!

Keithr726

Hey my PO was a weirdo that did some random stuff with my car. I guess I could just take a grinder to it. Plus I stayed up to 3am last night and I'm still a bit out of it.

Chris Prack

Don't make assumptions. Typically tires of the "same size" are not the same. On my 89 car with Cup 17" wheels my street tires do not rub. RA-1's rub a little in the rear. Hoosiers rub a little in the front and Mich PSC's don't rub at all.

They are all the same size tire.

If your car is good now don't **** with the sway bars. Larger front bar will give you understeer for certain. If the tires rub then you need to either, roll the fender, raise the ride height or respring the car. You could also give it more neg camber in the front.

333pg333

Probably best not to attempt a bandaid solution that is not really correct anyway. If you have the time and the money to get better suspension then do that, if you don't then maybe leave it until you do. What sort of camber are you running? Maybe just a bit of neg will help your rubbing issue and give you some better turn in?

TRP951

so if I went with mo30 bars front and rear I would stiffen the rear to help with understeer? This is on stock koni suspension

gt37vgt

changing your front chamber or castor is going to influence this rubbing as the wheel is in a different position could be better or worse.
and 95ONE i would sujjest the trangulated sway bar mount stiffeners the sway bars stays were you left it this way . works for me i have a standard bar above the control arms real close to the ac when it was there

Norm Swanberg

Thanks for the input. The springs are stock and not cut. They may have lost some tension due to time. The wheels are stock phone dials. They are rubbing at the top of the wheel well, not the fenders. I do not think offset is the problem. I feel my car leans more than I would like. The only time I hear rubbing is when it is leaning. I don't think stiffer sway bars are bad, even if they don't solve this problem. They should at least help. Maby I will need to go to stiffer springs, but sway bars seems worth a try. With luck 2 degrees negative camber in the front and 1.5 in the rear will offset the stiffer front sway bar and it will be neutral. If the rubbing is solved but I still have understeer, then I need a bigger rear sway bar. If it still rubs I need stiffer springs. Does this sound reasonable?

I did not make assumptions about tire size, based on the numbers. 205/55 vs 225/50. I stood the two together with the same tire pressure and put a level on the top. It said they were the same height. The 205's were worn and the 255's new.