Good starting point for track setup for 991.2 RS?
10-18-2022, 06:01 PM
#31
Does the car come with any shims front and rear from the factory? I purchased a car second hand and am trying to get it back to oem there are 3 shims on the front and rear arms. I’m trying to figure out if i should remove all of them or 2
2019 GT3 RS
I'm on my 3rd alignment, going for the 4th one next week. Stock rear toe on all alignments (range is 0.13-0.22 degrees per rear corner, I measured 0.20 degrees and has been set there), 0 toe front.
- Stock car came at -1.7 camber all around, good for street driving but on the track the MPSC2 rides beyond the tread marks eating the shoulders. Stock rear bar came full stiff, front bar in the middle (it has 3 holes). Car understeers badly on low and low-medium speed turns. The Porsche Track App has an understeer/oversteer gauge, so you can also validate there. Don't use a cell phone as a GPS, use a VBox Sport (20Hz) so g-meters and GPS produce real speed and g data, rather than dumping fake numbers from the onboard speedometer and erratic smartphone reads.
- 2nd alignment: -2.2 at all corners. This is as much as I could get with the shims that came with the car (7mm front + 1mm for a bracket, 3mm rear). Rear tires almost there, front tires need more camber. Went full soft on the front bar, reduced understeer, not yet balanced to my taste, but almost on the good spot.
- 3rd alignment: -3.0 camber front, -2.5 rear. Rear tires are on the spot, hot pressures at 32-34psi, perfect. Car understeers more, but front tires even at 28psi were not using a good 12mm of tread, so -3.0 is too much camber for MPSC2. I would not set them at more than -2.5 camber for the front, and run them at 29psi hot, but the car will still have a tad of understeer as above.
I think the understeer problems are coming from 2 factors: spring rates and rake. The .2 GT3RS went 220% stiffer on the front springs and just 33% at the rear. Then rake doesn't look right. My .1 GT3RS measured from the jack points (the 4 jack points) had 100mm front height and 130mm rear height on stock wheels/tires, with an estimated rake of a little over 30mm (because true rake needs to be measured from the center axles or close to them).
My bone stock 2019 RS came at 135mm LF and 133mm RF height, and 149mm LR and 150mm RR, this is a 15mm-17mm difference on rake, and the old saying on 997 and 991 GT3 Cup setup talks about 1" (25mm) rake as a good start. I went to reduce the front height to gain positive rake, and all it could go down was 8mm, car ended 127mm LF and 125mm RF. My car has FAL. I lowered the rear 10mm (6mm on the shock body or 4 turns, but the rear has a close to 0.6 motion ratio), ride height was 139mm on one corner and 140mm on the other. Rake pretty similar to stock, but still far from my .1 RS rake and ride heights.
For the 3rd alignment, I added a mass amount of shims, 9mm in the front, and 7mm in the back. The car dropped a lot on ride height, to the point that rear tires were rubbing on the front of the rear fenders. So I increased the rear ride height 5mm (2 turns) and removed 3mm of shims. By the way, with 10mm of rear shims the toe cannot get to spec, we maxed out the adjustment and the corners were still reading 0.6 degrees toe-in, so out with some shims. New ride heights LF 118mm, RF 119mm, LR 137mm, RR 138mm. I gained a little bit of rake, but car understeers on the limit as not only the front camber is too high (-3.0) but also caster went up by close to 1 degree (9.8 caster on one corner and 9.9 on the other), so the right balance should be adding just 4mm-5mm of shims to the front and setting front camber at 2.5. This for MPSC2.
I'll be setting the car for Hoosiers, but the folks in Indiana are doing some measurements for me as I might run different sizes this time for a little extra grip. The target should be 25mm rake, and not the 15mm rake the car came with (with its matching understeer).
I'm on my 3rd alignment, going for the 4th one next week. Stock rear toe on all alignments (range is 0.13-0.22 degrees per rear corner, I measured 0.20 degrees and has been set there), 0 toe front.
- Stock car came at -1.7 camber all around, good for street driving but on the track the MPSC2 rides beyond the tread marks eating the shoulders. Stock rear bar came full stiff, front bar in the middle (it has 3 holes). Car understeers badly on low and low-medium speed turns. The Porsche Track App has an understeer/oversteer gauge, so you can also validate there. Don't use a cell phone as a GPS, use a VBox Sport (20Hz) so g-meters and GPS produce real speed and g data, rather than dumping fake numbers from the onboard speedometer and erratic smartphone reads.
- 2nd alignment: -2.2 at all corners. This is as much as I could get with the shims that came with the car (7mm front + 1mm for a bracket, 3mm rear). Rear tires almost there, front tires need more camber. Went full soft on the front bar, reduced understeer, not yet balanced to my taste, but almost on the good spot.
- 3rd alignment: -3.0 camber front, -2.5 rear. Rear tires are on the spot, hot pressures at 32-34psi, perfect. Car understeers more, but front tires even at 28psi were not using a good 12mm of tread, so -3.0 is too much camber for MPSC2. I would not set them at more than -2.5 camber for the front, and run them at 29psi hot, but the car will still have a tad of understeer as above.
I think the understeer problems are coming from 2 factors: spring rates and rake. The .2 GT3RS went 220% stiffer on the front springs and just 33% at the rear. Then rake doesn't look right. My .1 GT3RS measured from the jack points (the 4 jack points) had 100mm front height and 130mm rear height on stock wheels/tires, with an estimated rake of a little over 30mm (because true rake needs to be measured from the center axles or close to them).
My bone stock 2019 RS came at 135mm LF and 133mm RF height, and 149mm LR and 150mm RR, this is a 15mm-17mm difference on rake, and the old saying on 997 and 991 GT3 Cup setup talks about 1" (25mm) rake as a good start. I went to reduce the front height to gain positive rake, and all it could go down was 8mm, car ended 127mm LF and 125mm RF. My car has FAL. I lowered the rear 10mm (6mm on the shock body or 4 turns, but the rear has a close to 0.6 motion ratio), ride height was 139mm on one corner and 140mm on the other. Rake pretty similar to stock, but still far from my .1 RS rake and ride heights.
For the 3rd alignment, I added a mass amount of shims, 9mm in the front, and 7mm in the back. The car dropped a lot on ride height, to the point that rear tires were rubbing on the front of the rear fenders. So I increased the rear ride height 5mm (2 turns) and removed 3mm of shims. By the way, with 10mm of rear shims the toe cannot get to spec, we maxed out the adjustment and the corners were still reading 0.6 degrees toe-in, so out with some shims. New ride heights LF 118mm, RF 119mm, LR 137mm, RR 138mm. I gained a little bit of rake, but car understeers on the limit as not only the front camber is too high (-3.0) but also caster went up by close to 1 degree (9.8 caster on one corner and 9.9 on the other), so the right balance should be adding just 4mm-5mm of shims to the front and setting front camber at 2.5. This for MPSC2.
I'll be setting the car for Hoosiers, but the folks in Indiana are doing some measurements for me as I might run different sizes this time for a little extra grip. The target should be 25mm rake, and not the 15mm rake the car came with (with its matching understeer).
