997.2 GT3 New MPSS 19" stock wheels, after 5 days of tracking in Souther Cal popular tracks, outer treads gone while inner treads still 80% remaining. Chamber F/R -2.1/-1.9 minimal rear toe in. Hot pressure F/R 36/38 psi. Does anyone have any experience with MPSS on the track? At what tire pressures? Either the wall of the MPSS is weak or my tires were underinflated.

Thanks.

 

I run the same hot pressures as you: 36F/38R. I've only done a few track sessions so far on the MPSS. I may increase the fronts just a bit to 37 because I'm starting to see wear beyond the rollover indicators on the side of the tire. I find running more pressure in the front also decreases understeer and helps the car turn in better.

 

On the 997 general forum, one guy suggested low 40's for the street tires. I did run a faster time with higher tire pressure in the low 40's because the prev session was cold and wet and I didn't get the chance to adjust the pressure. Given the $1500/set cost and it lasted only 5 track days for me. I'd suggest you get a pyrometer to see what a proper tire pressure should be on the track. I wrote Michelin about it and they have not got back to me. I read some where that a Pyrometer costs $300 and if you can extend your track days to 7 to 10 days on a set of PSS, then, you have gained back the money you spend on the pyrometer. However, this is just a speculation. It may still be the inherent wall weakness and different rubber materials on the outer and inner aspects of the tires. I will hold off buying another set until more info is out there. $500 per day for the tires on the track is pretty harsh!

 

What cold pressures are you starting with?
I start with 29 F and 30 R.
After a track session, the hot pressures vary
depending open the track temp, how hot a day it is,
and how long the track session was.
Because of these variables I don't even bother to check hot psi's.
Mr. B

 

The cold pressure is usu F/R 30/31 psi range so the the hot pressure does not reach beyong 40 psi

 

I agree with jakegt3, 36F/38R hot. Wear has been good so far after 6 track days.

 

36/38 hot were my targets during my 5 track days, and this is what happened. I am attaching a pic. I am at a loss.

 

Perhaps your alignment is off.
Mr B

 

Perhaps. The car tracks straight and the uneven wear occurs on all 4, though. I will have my susp guy look at it.

 

As an additional data point, I have run 5 track days on 19" MPSS and haven't had any type of uneven wear problems. I have been targeting 38F/39R hot. I tend to debrief for a while with my instructor before checking pressure, so it might even be a degree or two higher. This is on a 996 GT3. I'll update the thread with my alignment settings when I get a chance. I have been very happy with the performance of these street tires.

 

Wouldn't be surprised to hear that your alignment is off.
PLS let us know.
Mr. B

 

These are street tires so the sidewalls are not as stiff as DOT track rubber. Most of the time you need to bump up the pressures to prevent/reduce the roll over effect from the lateral g-forces.

Also there was chunking on the over edge. The rubber got too hot during a session so if your straights are not long enough then you are not getting any cool down time.

Another thing is you may want to add more negative camber to the car. I ran -2.5F and -2.0R and my tire wear was great. I think I could have gotten by with -2.2 in the front based on the wear patterns but-2.0 in the rear kept the wear above the wear bar indicators.

I would try 40F and 44R hot next time for a session or 2 and check the tires.

 

MORE CAMBER: A least 2.5 front and 2.0 rear

 

Agree. The car is at alignment shop now. The expert recommends -2.5 all around given the tire wear. And, more pressure for these street tires, in the low 40's hot. I will followup on my experience later.

Thanks.

 

My driver rear alignment was a bit off at -1.7 as supposed initial -1.9. That would make sense that that particular tire took the most beating and developed chucks to the cord. Will reset to -2.5 all around and aim hot pressure at 40's in the future.