LJpete

Hey Guys,

I ran my car (99 996 C2 bone stock) yesterday in a local autocross and found that my Michelin Pilot Sport 2's got progressively greasier with each run. To the point where my first run of the day was my fastest. The interesting thing about it was my tire pressures where not really all that bad (38lbs hot). The tires felt warm to the touch but not hot (perhaps I'm too used to R's and the temps that they can get to).

Does anyone that runs these tires know if they tend to over heat in ambient temps over 85 degrees? If so do you use a water sprayer to keep the tire temps down between runs and does it help with this tire?

Interestingly enough, I ran the car a month ago and the ambient air temps where a few degrees cooler and the track definately didn't have the same grip but the car I felt performed better in terms of tire/grip consistancy in the last event.

Any tips on camber as I'm wearning the second tread block row in my front tires?

Thanks in advance,

Pete

Jim Michaels

I have not experienced that effect with PS2s, but I only run PS2s when the weather is very cool. Your pressures seem fine from my experience. I doubt that the tires overheated during autocross runs. I've never felt the need to water PS2s or Michelin Cups between autocross runs. The problem is that it is just too easy to overdrive even the best street tires because they don't provide as much grip as we'd like.

What you may have experienced is the "throttle effect" (my own label). Maybe your autocross plan is like mine. I drive conservatively on the first run; making sure I stay on course and miss cones; just record a clean run. I try to gradually increase speed in subsequent runs; braking harder and later, and applying more throttle sooner coming out of turns. That's when I curse the tires for not having sufficient grip.

Just the usual camber tip; more negative camber is good.

springgeyser

+1. Drove on PS2 with no more than 38# hot and never got it up to over
120ish in temp after a AX run.

springgeyser

+1. Drove on PS2 with no more than 38# hot and never got it up to over
120ish in temp after a AX run. I would not think overheating is an issue.

LJpete

Interesting.

My philosophy on driving is not to exceed the car and just work with what I have. I usually just feel out the car on the first run as the tires are cold and then try to clean it up a bit here and there. My first run was a bit sloppy so I know there was more time in the car but the front tires where not consistant which I found was the problem. This worked in the last autocross as the car got better with successive runs, but this time the car just didn't carry a consistant amount of front grip run to run. Hense my confusion as to what was going on. Maybe the tires are going away? I thought I was was overdriving the car too but on each successive run, I extended my brake zone and on my 4th run it was over 25ft braking earlier to set the front end and resulted in still more push than I'd prefer. Another theory I had was that section of the course was going away as I had decent grip in the first half of the course (my car is fairly netural as I can get ttos on most corners) but for the 3rd and 4th run I pushed heavily.

On my fun runs, I had to baby it on the trouble corner and I could only manage 3 tenths slower thany my best run. Although my fun runs where several hours later and it was quite a bit hotter by then.

I'm running it again in 3 weeks but at a different lot with more grip. We'll see.

Jim Michaels

Are your rear tires newer than your fronts? Old tires tend to harden and lose grip, but that wouldn't explain why the fronts lost more grip as the day wore on. If that part of the course had less grip, others would have been experiencing the loss of grip as well. I'd be interested in hearing how the tires do at the next autox.

LJpete

Yes, the fronts are older than the rears. At least a year older according to the previous owner. Other's where experiencing issues on that same corner as the day worn on.

MagnusB

Mine can get greasy at the end of the day at the end of a run when I have slid a lot with them, but my last couple of runs are always fastest.

Btw 38 hot is too high in my opinion, lower it to 34 or so.

LJpete

Wow, really 34 hot on autocross? I've never gone that low but my last autocross car (BMW E36) required higher pressures for street tires. Even on R's I was never that low.

Is that the consensus on the 996 to go 34 hot?

Kerry

I would always run 40psi hot with S03, S02A, Pilot Sport Rib, Yoko AD07 on my 996 C4. Had good traction, good wear. I'd get 'greasy' at an Evolution school if it was a hot day, but that's with 10 back to back runs.

fast_freddy

I run PS/2's in Auto-X, they are my fastest tire by a good margin. I run 33-34 hot (measured after a few runs) in the front (225/40x18) 42-43 hot in the rears (265/35x18). My fastest time is invariably my last or penultimate run of the day. I tried a set of Bridgestone RE-01R's and only found them to be fast if I can get consecutive runs in like a fun run type situation otherwise the PS/2's are faster by about 3/4ths second. I do not drive with a lot of slip angle on my tires which might be the reason I'm faster on the PS/2's as compared to the RE-01R's. In terms of alignment I run about 1degree, 15 mins neg camber nasically no toe in the fron a tiny bit in the rear with the rear sway set full on stiff but change the sway back to "regular" for street driving. The stiff sway bar setting in the rear makes the biggest difference for me time wise as 911 variants don't do too well in Auto-x typically but I consistently win my run group. Last year with a non adjustable sway bar and PS Ribs I was consistently 3rd-4th. I'd say tires are 1/3 of the equation, the sway the other 2/3rds.