Track tire pressure for P Zero's

I did a search on this in the archives but still wasn't clear on something. This is my first DE and the instructions I received from the dealership said to inflate the tires 10PSI OVER street pressure. I'm currently running my P Zero's at 34 front and 42 rear (i.e. two pounds below Porsche recommendations for both front and rear). The 10 PSI doesn't make any sense to me as the tires would seem to be overinflated once they heat up. Any thoughts? Thanks for the help!

Ten PSI's over the factory settings will kill you on the track. You should go lower because the tires are likely to heat-up faster and more than they would on the street. Most people run 32F/34R at the track hoping to achieve 40 psi hot pressures which is where you want to be.

Sorry, I should have mentioned that I have 18" tires with the turbo wheels on the car. Thanks again!

[quote]Originally posted by jimkuhr: <strong>Sorry, I should have mentioned that I have 18" tires with the turbo wheels on the car. Thanks again!</strong><hr></blockquote> The size doesn't matter.

Viken is one of the boarders who knows what he talks about, and I respect and follow almost all his recommendations. I just wanted that crystal clear, because having said that, this is one of his recommendations that I tried but don't feel comfortable following . The C4S has the same wheel/tire set as the turbo. At 32/40 cold, the scub marks in front were perfect but the scrub marks in the rear extended unto the sidewalls into the P of the Pirelli logo during a 2 day DE event. Didn't check them hot. Would not know what to do with hot pressures anyway. I'm thinking of trying 42 cold for the rears next, to see if the scrub marks will stay off the sidewall and also see if it improves the understeer under heavy acceleration. Definitely do NOT do 46/54. Thats the 10 lbs over recommended by your dealer, unless you want your car bouncing like a basketball.

For the track I start with 32/36 which is a good start. I adjust back to normally recommended 36/44 when normal driving. Regards. Mike

[quote]Originally posted by Palting: <strong>The C4S has the same wheel/tire set as the turbo. At 32/40 cold, the scub marks in front were perfect but the scrub marks in the rear extended unto the sidewalls into the P of the Pirelli logo during a 2 day DE event. Didn't check them hot. Would not know what to do with hot pressures anyway. I'm thinking of trying 42 cold for the rears next, to see if the scrub marks will stay off the sidewall and also see if it improves the understeer under heavy acceleration.</strong><hr></blockquote> I am not sure if I understand what you are saying but 32/40 cold is definitely not going to work for you assuming you are attempting to drive the car at least 7/10th on the track. Pretty much everyone agrees that "hot" temperatures of 40-42 psi is what works and you need to have your cold settings at 5 or more psi's lower than that. With your AWD car, you should find 32/35 quite acceptable for street tires. If my pressures are not working for you, it is quite possible that your alignment settings are not in the right places. I would have those checked.

[quote]Originally posted by Viken: <strong> ..... Pretty much everyone agrees that "hot" temperatures of 40-42 psi is what works and you need to have your cold settings at 5 or more psi's lower than that. With your AWD car, you should find 32/35 quite acceptable for street tires. </strong><hr></blockquote> Alright!! I finally have something to shoot for with hot pressures. Viken, what makes me hesitate is the scrub marks going on to the sidewall on the rears at 40 cold. I am pushing the car as hard as I can, which as a novice may indeed be 7/10. I don't know if it means anything, but I lap everybody at least once in my run group at Mid0hio doing 1:54 to 1:59 per lap. Is it alright for the scrubs to go that high? It is more of a scubbing, not a "worn" appearance on the sidewall. It looks more as if I curbed it all around the circumference of the tire, though I know I did not curb it. <img src="confused.gif" border="0">

The scrub marks, as you describe them, should not be a deterrent for you. Just make sure you are using the available tread through the shoulder.

Palting, Don't worry about the scrub marks. Just the hot pressures. Reason why the scrub marks are where they are is that you don't have enough negative camber and you are only using the outside half of the tire. Dial in some neg. camber and you will see a difference. As a novice you shouldn't be worried about times. But for your info. A 90hp Honda was running 1:58-59's at the Tracquest event. Your car is capable of 45's with street tires and a good alignment. Greg

Thanks, Viken and Greg. Boy, that must be one hot Honda suspension/tire set up. My cars alignment is set to stock/street specs on the C4S sport suspension. I plan on doing about 6-8 track events per year, and daily street driver most of the dry/warm season. How far can I deviate from the street specs without too much sacrifice on street driveability and tire wear? What numbers would you recommend?

Not sure what was done to the Honda, it was driven back and forth to the track but with track tires. As always the driver has more to do with the performance than the car. On the camber issue, I would think that anything more than 1 degree or so will adversely affect tire life. But as long as your daily drive doesn't just consist of straight line highway miles you might not see a big decrease in life. Heck these tires will only last 10K miles or so in the best situations. If you decide to go to some dedicated track tires you would want at least a degree front and rear to give the tires a longer life and more grip. No one answer, just try something more aggresive and see how it goes. A bunch of Porsche guys will be at an event at Putnam Park Oct 5 and 6. If you want an application let me know I can fax one to you.

Thanks, Greg. Also caught Mikes's -1/-1.2 post on a diff thread. Will start some trials next service visit. Hopefully he won't ask why and void the warrantee .