Decolliber

I just replaced 16" BBS wheels on my 1988 Carrera with 17" RUFs. Porsche recommended pressures for the stock 205/55R16 and 225/50R16 sizes are 29 and 36 respectively. The new tires are 205/50R17 and 255/40R17. I am wondering if I should increase the tire pressure or leave it the same (29,36). Those sidewalls on the back look awfully narrow.

dugsud

Just to bump this to the top again, I could really use some advice on this exact question.
Come on you guys running 17"s, what pressures do you recommend?

Bill Gregory

On 964's, Porsche recommended 36 front and 44 rear on it's 16's. Many don't run 44 in back more in the 38-39 range. On 17's, Porsche recommended 36 front and 36 rear. If it were me, and lacking better information, I'd set the fronts at 32 and the rears at 36. Then monitor the wear and adjust if needed.

Decolliber

An advisor at Tirerack.com told me to use the same pressures in the 17s as in the 16s. He said the load bearing capacity of, say, 255/40R17 is equal to or greater than 225/50R16. Hier pressures may cause excessive wear in the centre of the tire. I assume higher pressures are recommended for the 964 because it is a lot heavier (3200 lbs?) than a Carrera (2700 lbs?).

eddychan

Hi,

my 91 C-2 only weights 2970( 1350kg) according ( C-4 is 3190lbs and 1450kg) according to the handbook. So I do not know how you get 3200lbs ? Should the US spec car weight an extra 230lbs?? Or you are merely referring to C-4 only??

Anyway, my hand book suggests 36 around which I have used and am feeling very comfortable with. If you want to take into the account of weight reduction for a 911 then take 9% off and you should try 33psi (32.76 to be precise)

I also find the ambient temp makes a big different. I normally drop a couple of psi in the summer when the temp is up. I believe that hot air expands and PV =nRT so air pressure should up with the temp assuming that the rubber compound does not expand as much.

Regards,

Eddie
91 C-2