I received track alignment specs from Porsche Motorsport several years ago when I first got my car. I also paid a high profile factory driver to test my car and set up. Just to be sure. Now 3 years later at a new track....

Currently, when I track the car on a fast, smooth sweeping corner the rear slides out about a wheel width and then catches. I am not talking power drift or TTO here...the car is balanced throughout the corner. Its a gradual, but unnerving shift.

My rear bar is on full soft, as I was originally told. I am suspecting that this may be the issue, since I know of another fast GT3 on full hard.

Running Hoosiers and the most common camber settings. The car was also corner balanced.

Thank you for your input.

 

try one off full firm let the back end loose some

 

Do no simply look at the rear sway setting, as handling is based on the relative stiffness and softness of the front and rear bars together. Generally, if the front is stiffer than the rear, this reduces oversteer (or increases understeer). If the rear is stiffer than the front, this increases oversteer (o reduces understeer). 911's need softer rears relative to front to counter the rear-biased weight distribution. Given what you are saying, I suspect the front is also soft (front & rear at same setting). So your car is doing what it does naturally - swing the *** around. Keep the rear soft and increase the front stiffness until car feels more balanced through the turn. Once car is handling to desired balance (how car reacts at limit) and if there is too much body roll, simply increase the front and rear at the same rate so to preserve the relative difference. This keeps the balance as set, but reduces body roll more. Hope this helps.

 

Another thought. You should double check your alignment specs. You should do this twice a year if you track a quite a bit. Also, maybe your rear toe link is worn? I say this because if your setting worked before then all should still be good.

 

Responding to the last 2 pasts. I agree with the setting theory which is why the rear ended up on full soft in the first place. I will also recheck the specs and toe links.

I almost hesitate to call the reaction an oversteer. Its hard to explain...its more like a gradual sag then easy twitch. I can handle a nice predictable oversteer.

 

The set up sounds good to me. I am trying to get the snappy rear end out of my car, if you are running full soft in the rear I would either try stiffing up the front sway or putting a tic bigger spring in the rear, running more rear sway will lift the inside tire more making the car snappy. I am trying to go from full stiff to full soft on the rear bar, by way of spring rates. good luck. the good news is you can experiment at the track over the weekend if you are just making bar adjustments.

 

what kind of tires and hot pressures are you running

 

Hoosiers with 38 hot. I think that I started about 32 cold. Roughly...I only had a couple of sessions on them and did not take the time to read temperatures either.

 

if you are moving your GT3 on Hoohoos you are probably adding 8-10 pds pressure and were above 38pds hot...if you notice this less in your first few laps than in the later session laps you should be checking your pressures...as recommended for a 996 GT3 start out with one from hard front and rear...it works best for me

 

Thank you. What should the temps be warm in your opinion? (Using this as a starting point.)

Thanks, Karl

 

I shoot for 37-38 hot front and rear and I start out cold 10 pds below that unless it is an unusually cold track where I will go 8 pds...I'm on the west coast and track temps are usually 80 deg to 130 deg...out here the track continues to warm all day and once I hit my target pressures I continue to reduce as the track warms...you should get in the habit of checking pressures after every session...

 

I usually check the temps. I had 8 novice guests with me at our track and I never had the opportunity to work on my car. The car was doing this before the new tires were put on. I was running Sort Cups before.


I appreciate all the advice. I cannot wait to get back out and tweak.

 

I just reread your original post...has it been three years since you have had an alignment...this could very easily be a rear toe problem and you might be chasing the bars for no good reason...the rear toe links combined with the eccentrics can be a real problem to keep in proper alignment on the 996 GT3...if you haven't had a recent alignment it would be a good idea to get that checked for you chase setup...

 

Will do. For curiosity...what set up do you run for camber and toe?

 

for MPSC tires you can run less negative camber and still get enough heat in the tires 2-2.5 deg...but for Hoosiers I need at least 2.5 deg neg front/rear to get them to temp..on tight slow courses or autocross you can go even more...toe front/rear is user choice...a pretty neutral setting to start from is 1/16" total toe out (front) and 3/16 total toe in (rear)..