TT Surgeon

Thanks guys, just what I needed.

911

Bob brings up a good point about driving styles, etc., affecting the tire wear. I think the best advice is learning how to read "your" tire and adjust accordingly.

In my case, the rollover was excessive at the recommended tire pressures. Therefore, I did two things:

1) Increased negative camber from 2 to 2.5 degrees
2) Incresed tire pressure from 36 (hot) to 40 (hot)

I looked at my rollover at the end of my sessions and it was right where it should be. Consequently, the car felt a lot better to drive and it was much more controlled coming out of the corners (before it was stepping out).

Rich

jrgordonsenior

Bob what were those temps across the rear tires? I ask because the Sport Cups really need to be in the 190 range to work their best magic. I would also add that your inside temps should be incrementally higher than your outside temps if you have proper negative camber-especially on a heavy cars like ours.

DJF1

Been running the Cups for almost 3 years now. Car with driver is over 3300lbs which is not exactly light. Anything over 36 in the rear produces a greasy feeling, not very nice. Been keeping with the Michelin recommendations of 33 front 34-36 rear and always had even wear and temps. As a matter of fact one set really died because of too many heat cycles, not because of wear... Never corded a set and I'm running -2.4 front and -2.9 rear camber. At Sebring I had a lot of understeer to fight and I checked with the Michelin engineer who was on the track. He said to me that I should go lower front, keep the rear at about 35 hot and on my next oportunity to go with the 235 front to pair the 285 rears. I asked him about the diameter difference and he said that its not an issue and he has seen very good results on 911's with this combo. He too pointed out the need to run them over 180 degrees.

DrJupeman

I recently posted a thread about two MPSC failures on my car this year. I had been targeting 34 psi hot in the rear. I bumped that to 39 psi in the rear at the last event I was at and no problems so far. I shoot for 34 psi hot in the front.

Car is 3300#+ with driver, decent power...

Bob M

JR,
I guess I should have recorded the temps, but I didn't. I was only looking for changes across the tread. I know they were not in the 190 degree range though. My recollection was that they were in the 170 range though. This was after a cool down lap on the track and a big swing through the pits, so the actual operating temps were higher. How much would a tire cool down in this scenario -- any guesses? I will record the temps next time and pay attention to the inside to outside temp variance. Thanks for the tip!
DJ,
It seems like your experience is more like mine. Like you, I have never corded (flat spotted yes -- Damn!) my MPSC's. I also found the tires to feel greasy at higher pressures and I bought my latest set because the former tires had heat cycled themselves out. If this wasn't the case and I didn't care about optimum tire performance I probably could have put another weekend on them.

Bob

Bull

I also noticed an improvement in balance and wear when I moved from 225s to 235s in the front, with 285s on the rear.

ColorChange

OK guys, here is the presentation by Michelin on the MPSC's. It's in PowerPoint.

https://netfiles.uiuc.edu/tmccrthy/P...T?uniq=-5defqf

jrgordonsenior

Their last presentation page is for a NA-996 and they recommend 36-40 lbs. hot on a 285 tire. The early 996's weighs barely 2900 lbs..

I think it's remarkable how many different pressure experiences drivers have had with this tire. I think it must be related to car weight, even just a few hundred pounds, and tire size.....

George A

I soooo agree with your statement. I've seen people run them at 40 with success and I've seen people run them at 34 with success.

I'm in the low pressure camp myself.

I've gone through a set of 235/295 on a 993 C2 that weights about 3100 lbs. I got the best performance and even temps at 34 psi hot all the way around. I run 2.5 degrees of camber all the way around. I tried higher pressures but it felt squerly. At first I had a hard time getting them up to temp but now it's not that difficult. I've switched to 225/285 now just to test some things out.

I'm actually tempted to raise the pressure a little just to see if they feel better now that I know how to get them up to temp.

Finally, do you guys get much noise from them? Mine squeal way too much. I like it because it tells me I'm close to the edge but then I hear from others that they barely make a sound.

George

Bob M

Mine are pretty darned quiet. I can attest to the fact that when they give way, there is no warning too! My off track experiences took place at the end of last season which made me think about all of the heat cycles I had into those tires. Even though there was life left from a tread standpoint, they stopped "sticking" like they had done to that point and became a bit unpredictable. This was the main reason behind me replacing them. I figured that sitting in storage through a 2nd winter probably wouldn't have helped the situation either. Any thoughts on the effects of storage temps on track tires in general?

Bob

38D

Yes, there does seem to be a large variation. I have a '91 964 Turbo, 3000#s, and run 235/295. I run them 33-34 hot all the way around. (actually what I do is bleed them down to 32.5 when I'm in the pits, about 2-3 mins after the run). Wear has been very good (14 DE/Practice days on one set, 2 race runs on the other set). When the pressures are much higher than this, I start to get the greasy feel.

DJF1

Hey George, please do share your tips! Sometimes I really have a hell of a hard time to bring them up to temps....

ColorChange

I don't think normal storage temps have any affect. Keep them away from sun though.

George A

Danny, there is no big secret way of getting them hot. I just try to slide the car as much as possible, especially in the slow turns where I know any breakaways are easy to catch. There are a couple of slow turns on the track I drive the most, while most just take their time through them, I push it over the top hopping to get/keep them as hot as possible. I've been lucky so far and am starting to see temps in the 210-230 range on the tire with the most load.

George