InTheAir

I know this topic has been beaten to death, but I can't seem to find a source for info on HOT tire pressure in the following scenario:

DE
997TT
Michelin PS2 (8000 miles; 70% tread front; 50% tread rear)
stock alignment

This past weekend I had my first DE and ran the pressures stock to begin with (33/39). After a session, the HOT pressures were 39/46.

I drove the whole time with PSM OFF (instructor insisted ) and Sport ON.

During the early sessions, it was on a dry track. In the later sessions, it was in the rain.

The rear end was coming around on me quite a bit, with very little to no tire squeal beforehand.

I realize that most of this is probably my driving, but I'm curious if the rears were over inflated or fronts under inflated?

(I initially posted this in the 997TT forum, but I suspect this is a better place for it.)

eclou

Jeff, Michelins work better if you drop the pressures to mid 30's hot. You will need to start in the high 20's cold and bleed off from there. Best way to determine the setting for you would be a contact pyrometer.

InTheAir

Thanks, Gene.

When you bring the rears back to mid-30's hot, are you then running with the 'flat tire' message?

Bull

Are you suggesting that he run his street tires (PS2s) at the same/similar pressures that work for MPSCs?

Bill Lehman

With a Cayman, I'm running PS2s at 36F and 39R Hot and yes, I do get the "Flat Tire" message when the tires cool. It stays on until I put the recommended amount of air back in. I plan to try about a # lower all around at the next DE

FTS

In my experience as well, 34 front and 36 rear hot worked the best; granted it is a Cayman, but mid-30s are the right range for PS2s.

Turbo Stan

Personally I think your instructor is an idiot If he wants to risk his own $150g car, let him. There is just no good reason not to have it on. The PSM will come on only when you are losing control of your car. From that you will learn its limits. The only point where you should drive with it off is when it is actually hurting your lap times.

smackboy1

I was having this exact conversation with a friend of mine at a DE this past weekend. He was driving a stock 996TT w/ OEM Pirellis. We are both in the beginner run groups too, so we brought an instructor into the debate. This is the gist of what I took away from that conversation.

I think the answer will be different depending on the car, the tires and driving style, but the general idea for my car was to have the hot pressures at around 36F 38R. A hot pressure of 40+ was overinflated for me. For my car this translated to cold pressures of about 28F 30R. It might be different for you. If the tires are overinflated, they will feel a little greasy. The car will be sliding all over the place. This might happen at the end of the run session when the tires are at the hottest. If the tires are underinflated, they will flex more and will feel they are rolling over onto the sidewall (which is exactly what they are doing). Also, the extra flexing of the rubber will cause excessive heat build up and lead to overheating which can lead to chunking of the tire tread. You can check for roll over by putting a dab of white shoe polish on the shoulder of each tire (with a little overlap onto the sidewall) before the run and take a look after the run to see where the tire is making contact with the road. If the shoe polish is rubbed off the sidewall then the tire is rolling over and is under inflated. If the tire is only making contact in a narrow band in the center part tread, the tire might be overinflated (the center is bulging out).

It's helpful to find a more experienced drover who has the same car and tires as you do and ask for their tips after showing them the results of your experiments with the various pressures and shoe polish.

When you are all done at the track, don't forget to pump your tires back up to street pressures because they will probably be way too low.

eclou

Yes Jeff, the flat tire symbol should be on. Just ignore it.

Crazy Canuck

PS2s, above 38PSI Hot are very greasy.

CoGT3

Any suggestions for Pirelli PZero Rosso tires? (not the DOT-R, the N0 street tire) I am running them on a 07 GT3.
Thanks

InTheAir

Stan -

As a newbie, I ~thought~ I would have the opportunity to set my own car. I intended to run in a few different modes to see the difference. However, to my surprise, he wanted me "to run without PSM so that the car isn't helping me go faster than I can safely go." The theory being that with the help of the PSM, I could be in 'more' danger.

However, like your comment, there is a lot to be said for using it as a newbie. I will definitely know when it kicks on (thus showing me I've pushed too far), and the added safety might be very useful. It could have been in my case.

smackboy1

I had PZero Rosso's. IIRC they don't grip well beyond 40 psi hot and then they are pretty greasy feeling. I overheated mine and they chunked. I replaced them with Yokohama ADVAN Neovas and compared to the Pirellis I think they are much better tires. Better grip all around.

smackboy1

Keep in mind that PSM is never completely turned off. Even when it's switched off it still monitors the car position and if things start going pear shaped and you hit the brakes, PSM will activate and attempt to remedy the situation.

If you want to experiment with PSM off try autoX. Low speed but lots of oversteer/understeer possible.

InTheAir

Well, I had a spin (180 degree, remained on the track) and I didn't feel any PSM helpin' out.

I also spun (180 degree, rolled asswards to the in field grass) in the driving rain and I didn't feel any PSM help.

What exactly will it do when it's in the off position? (honest question)