Topcot

Just purchased a '95 C4 Cab with Michelin Pilot Sports 205/50ZR 17 on front and 255/40ZR 17's on rear. Factory manual says 36# all around for the C4. Any thoughts on this for street driving? Thanks, Topcot

95 C4 993

34 in the front 36 in the rear. At least thats what I do.

trickydisco

look at the door jam sticker:

mine says
36psi in front 225/40/18
44psi in rear 285/30/18
so it depends on the rubber

congrats on your purchase

Bull

993s with 17" wheels call for 36 front and rear. I found that worked fine for my NB with 17s.

18" wheels will be 36/40, or 36/44 depending on the wheel and tire.

AM993

I am also running 36 front and rear on 17". Works fine.

24FPS

@ cold... i keep 'em @ 36#f & 38-40#r(their 285's).

this is what i was advised to run 'em @ by the guys @ wheel enhancement.

alot of p-peeps run 36# all around fwiw.

FlatSix911

I also have been running 36psi in the front 225/40/18 and 44psi in the rear 285/30/18 tires.

Just curious as to the logic behind why Porsche recommends the higher rear tire pressure with 18 inch and not with 17 inch wheels?

FlatSix911

bump...

KOAN

I'd guess to protect the wheel from getting bent. The higher pressures would help offset the vulnerability of the wheel due to the shorter sidewall with 18s.

CP

I think 40 to 44 psi in the rear is a little high, even for 18". I run 34/38 F/R cold in my 18" Ruf wheels. I wouldn't mind going down to 36 in the rear actually.

CP

InTheAir

I adjust my tire pressures to achieve about 40 psi in all tires when HOT. When they cool back down, it is usually 38 in the front and 36 in the rear.

jdistefa

In general, the wider the tire, the more pressure is required to keep the tread wear even. Too low, and the margins of the tire will wear more quickly, too high and the centre will wear prematurely. Given that 18" tires generally run with 265-285 tire widths, vs. 255 for 17", that probably explains the difference in recommended pressures.

With 285/18", I usually run 40 in the back - a good balance between grip/ride comfort/wear, and with 225/18, 34-36 depending on temp.

Pedro356C

on 18", I'm running 36F and 38R...

clib

I am on my second set of 17 Pilot Sports and have run 34-36 psi front rear - doing that the wear was very even across the width on the first set of tires even at aggressive alignment settings. For street use anything above 36 was noticeably harsher and not recommended on the 17 in. wheels regardless.

bill