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Old 12-05-2012, 12:38 PM   #11
Certified Boxster Addict
Join Date: Nov 2010
Location: Los Angeles
Posts: 7,665
As Brad noted above, everything is a tradeoff and the trick is to find the sweet spot for your specific car, tires, and level of driving skill.

Its not that we don't want to share our "secrets" (hah, I wish I had some!), its more that we don't want to give you advice that might not help or advice that is all over the place. A lot of "racing" forums will be stacked with guys who have 911's and what works for a 911 won't nesscessarily work for a mid-engined Boxster. And even here in the 986 world, what works best for me (full spec suspension, lowered ride height, lots of negative camber, r-compound tires, and 50+ track days driving experience) might not work for you.

With that being said, in general, you probably want to start by lowering the rear tire pressure to get more rear grip. While doing this, you'll want to monitor how far the tires (front and rear) roll over in the corners to make sure that you're not going too far onto the sidewall. There are little diamond/triangle markers on many tires that you can use as a reference to gauge this. If you get too much tire roll, then increase the fronts and rears by 1-2 psi and test again.

Also, you'll want to find what tire pressure results in the most grip. Some tires grip more with lower pressures (around 30psi hot) and other tires grip better with higher pressure (mid-to-upper 30's). You'll also have to determine (most through experience) how much pressure buildup you get between cold and hot (dependent on your driving style, the track, the exact tire, and the weather conditions). With all of that being said, I agree with Topless' advice that a goal of 36 psi hot (front and rear) for your Hankook V12's is probably a good goal (start with fronts and rears at 32psi cold).

As you can see, you are trying to control several variables (grip, tire roll, pressure gain from cold to hot, etc) with one input (starting tire pressure) so its not as simple as "just set the tires at XX psi" kind of answer.

Hope this gets you heading in the right direction.
1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor

Last edited by thstone; 12-05-2012 at 07:48 PM.
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