Tire Pressure? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Mr. Boone · 09-10-2005, 08:05 PM

My car is fitted with Good Year Eagle F1 tires (oddly enough made in Germany) 225/40ZR18 92Y Front and 275/35ZR18 95Y rear. Can anyone recommend the proper tire pressures for these tires?

Jeph · 09-11-2005, 08:40 PM

I've read a lot of books in my day and none of them will change your life like the Holy Bible. But brutha, next on the list is Boxster/Boxster S Manual. It's definately worth the investment (both timewise & financially).

From system checks to warning lights, tire pressure rates to bulb sizes -this book has it all! Detailed illustrations make this read a piece of cake! Oh, and there's one special twist at the end when the Boxster... well, I'm not gonna give it away, you'll just have to read the book.

Mr. Boone · 09-11-2005, 09:14 PM

Ah, Ya, I actually received all the manuals with my car and somewhere very near the front are listed the recommended tire pressures. Your right, these manuals, although not quite as valuable as The Holy Bible, are quite informative. Trouble is the tires on my car that I listed are not the tires Porsche put on the car. I think that matters. Right? I'll check Good Years website as well.

Perfectlap · 09-12-2005, 06:02 AM

the manual recommends pressures that are way too conservative for abundant understeer.

deliriousga · 09-12-2005, 08:37 AM

29psi front, 36psi rear (YM 2000, YMMV).

It doesn't matter what tire you use, the pressure is determined by the vehicle and its' performance.

limoncello · 09-12-2005, 11:34 AM

Trick question: How do you reduce/eliminate the factory understeer, and get closer to neutral:

a. Set fronts 2 psi higher than rears
b. Set rears 2 psi higher than fronts
c. Increase psi uniformly in all four tires

Reason I ask, I have seen both answers a and b in other forums. Would seem only one could be correct.
June track day: I ran 36/36 cold based on advice that the fronts need more psi for turn in. Wound up about 40/40 hot. You could feel the understeer.
Friday track day: started 34 rear/32 front (cold) and wound up around 40 rear/38 front (hot). Car felt better balanced, but still with some mild understeer. I could get the tail loose if I worked on it. 90 degree day.

Comments:
- Seems to support "b". Wonder where "a" came from?
- Not sure I want to go to oversteer (would get a 911 for that). Neutral is nice.
- R/F 36/32 (cold) works fine on the street.

Open for comments/discussion -