When i was at my first DE event there was alot of discussion around tire pressure. It seems most people started pretty close to the recommended pressure, then as the tires heated up some air was removed. For most 987 and Cayman owners the best place to be was 40 psi for all four wheels hot. Hot meaning after the car has been driven hard for awhile and the air has expanded.
Ultimately, this means we were removing air from the rears b/c they would end up at 42psi plus once hot.
__________________ 05 987 S SOLD
Arctic Silver
Bose/Xenon
The best traction on most tires is acheived by running the lowest pressure at which the tire won't roll over onto the sidewall during cornering.
With our V710 autocross tires (245/35/18 front, 285/30/18 rear) we run 30psi front / rear on medium traction surfaces. Couple psi higher if it's a high traction surface and a psi lower if low traction.
I have found that to dial out some of the inherant understeer, I run 36f/r and often bleed out the rears in an Autocross environment. Ideally, you want the hot pressures to coincide with the tire manufacturers guidelines. These may be hard to find for "street" tires, but for competition tires, its quite easy.
John.. you run PCA events or only SCCA? Not sure if SCCA is running locally this weekend, but Chesapeake PCA is at Ripken on Sunday (Fathers day).
My first 2 DE's I left the tire pressure at normal 30fr/36rear as I could not find anyone to give me a straight answer. On my 3rd DE the general concensous was standard plus 5 and let the air out as they heat up. I noticed the car getting squirilly (sic) in the rear end towards the end of the day. on my 4th DE with stock +5 lbs I lost control of the car in the 3rd session. I am going back to 32/36 to see what happens. Of course my DE tires are Continental Conti Sport 2 which I am finding out are not considered to be the best tires for the track. I am going to try my Michelins this weekend and see how they do.
I have found that to dial out some of the inherant understeer, I run 36f/r and often bleed out the rears in an Autocross environment. Ideally, you want the hot pressures to coincide with the tire manufacturers guidelines. These may be hard to find for "street" tires, but for competition tires, its quite easy.
John.. you run PCA events or only SCCA? Not sure if SCCA is running locally this weekend, but Chesapeake PCA is at Ripken on Sunday (Fathers day).
BMW club runs on Saturday at Ripken and the SCCA has an event at FedEx on Sunday, so I'm all booked up.
Depending on what tires you're using and what size wheels they're on, you might find you'll go faster with lower pressures. 36 f/r would be much too high for a boxster on V710s, for instance, but for Hoosiers that may be about right. Victoracers and RA-1s require higher pressures as well.
My first 2 DE's I left the tire pressure at normal 30fr/36rear as I could not find anyone to give me a straight answer. On my 3rd DE the general concensous was standard plus 5 and let the air out as they heat up. I noticed the car getting squirilly (sic) in the rear end towards the end of the day. on my 4th DE with stock +5 lbs I lost control of the car in the 3rd session. I am going back to 32/36 to see what happens. Of course my DE tires are Continental Conti Sport 2 which I am finding out are not considered to be the best tires for the track. I am going to try my Michelins this weekend and see how they do.
It is entirely possible you overheated the rears. If that's the case, a bit more pressure all around might help.
The Boxster is harder on its rear tires than it is on the fronts.
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