drodg

I am putting a set up 17" cup wheels with Bridgestone Potenza's on my 89 C4 today. I am leaving the old 16" wheels. My question is what air pressures are you running in your front and rears for normal daily driving? Thanks

jimq

36 both

Red rooster

Jim has that 100% . If you dont get that right ,the handling is awful !!
All the best

Geoff

boxsey911

I'm quite shocked to hear these pressures and while I'm not doubting the greater knowledge of you guys my manual (MY 1990) says 36 front and 44 back

Do these figures apply only to the original wheels but don't apply to my 17" Cup1s? And surely a rear-engine car should run higher pressure at the rear?

Just looking for reassurance before running outside and dropping the pressures.

ilko

Boxsey, your manual refers to the D-90s - the standard 16" wheels on MY1990 cars.

drodg

That's interesting I had a RS America a few years ago and thought I always ran different air pressure front and rear.

boxsey911

This could partly explain why I've been experiencing a 'fidgity' back end under heavy braking. I'll drop the pressures to see what happens.

craig001

I run 36" rear/34" front ona set of 993 Targa rims on my 964. But you really need to drive the car and see what combination you like best.

Red rooster

Porsche tire specifications are

16 inch cold tires front 2.5 bar rear 3.0 bar

17 inch cold tires front 2.5 bar rear 2.5 bar

If you have 16 inch pressure on 17 inch tires the car will handly really bad !!!

OK , you can play with +- 2 lbs but its a good straight place to begin with the factory pressures. 3.0 bar ( 44 lbs ) on the 17 inch rears are a nightmare.

Good luck !

Geoff

drodg

I got the 17" installed this afternoon and Tire Rack had set the psi at 36. I went out and drove the car and it handles great but it seems to ride better than my 16" tires did. It could be the psi difference, but I honestly can't remember what we set the original tires at. I expected it to ride stiffer because the shorter sidewall, nice suprise. The difference in the looks as you all know is incredible. It reminds me of my RS America I had back in 94.

boxsey911

Thanks again there was nothing in my manual about 17" tyres. Yes, handling has been a little vague when pushing on. Pressures now dropped ready for the morning.

Steve

Mike_964

When I bought my C2 it had 2.5 bar in front and 3.0 bar in the rear on 17 inch wheels, and it drove perfect all the way to 160 mph.
I later changed my rear tires (same brand) and again put in 3.0 bar in the rear, and the car handled like I ran on flat tires in the rear, but first when I drove above 80 mph. I turned to rennlist and got the respone 2.5 both front and rear. A little reluctantly I tried to lower the pressure to 2.5 bar, and again I could take it all the way to 160 mph, without any problems.
So I guess the former owner just never drove the car very fast, and when the tires where worn it didn't matter anymore.
I also got fooled by the sticker in rear of the car, but apparantly they changed from 16 inch to 17 inch just it left the show room.

Red rooster

Steve,
Many years ago I used 2.5/3.0 on 17 rims once down the road. That was either chuck the tires in the trash bin or find out what to do !
Maybe I am not as brave as most people and if Porsche tell me what is needed I listen .
Be good to hear what happenes to you in the morning !!

All the best

Geoff

Reformed

Ive played with the pressure with 17s but for me ive found that 36 all round is best.

dfinnegan

I don't consider myself very knowledgeable at all with these cars as this is my first one and even I noticed a big difference when I put 3.0 in the rear of my 17's. After searching a bit and setting them back down to 2.5 I was much happier.