As many of you know I replaced the tires on my A8 with 245/45/18 Dunlop SP Sport 9000 tires. They came from the tire mounters set at 45psi. I lowered them all to 32psi cold. Was that a good idea? How can I determine the best tire pressure? I will listen to any suggestions. Thank you.

Out of curiosity, why did you lower the pressure?

Two reasons, my Corvette posts best track times with this pressure and I worked at a tire shop for a while when younger and every tire that went out had 32 cold in it. Nothing scientific though.

Normally, quattros run slightly higher pressures at the front...

Most C5's I've seen are set up with 32 in front and 34 in the rear, Vipers have a higher differential, and opposite for GT vs drag.

On the A4's, we run 36psi all the time, just what I'm comfortable with, and then 40 at the track. PZeros max at 40.

On the 911, I run 38 in the rear and 36 in the front, cold. I play with that in the summer, etc., but you're probably in the right ranges. Honestly, on a car like the A8, anywhere in the mid-thirties is going to make the car happy, just make sure the front two have the same pressure or you'll get significant pull toward the low side.

Not much science to it...

Cameron

Bart
With only 32lbs I would be a little woried about a bent rim. On our 4.2 17" 9000`s I keep 40 lbs all around. Did you play around with tire pressure when you had yours?

I have been driving a number of cars around with tires at 32 and less. Never had a rim problem. The 245/45/18 tires are fairly low profile but not that bad. Another car I drive at 30-32 has 315/30/17 tires on it. Those suckers are SHORT on the side. Hit lots of bumps, never a problem.

I never even checked the pressure on the A6 4.2, sorry.

I just want the best combo of performance, wear, fuel mileage, and noise levels in the A8 setting. It does seem grippier at 32 then it did in the high 40's for sure.

... time. Besides Dunlop are tires to avoid

The responses to this question seem a little odd. The tire itself carries the max. pressure rating (usually mid 40s psi on higher performance tires nowadays), and here's what the performance driving trainer at Skip Barber told us when I attended a class back in the early 90s:

1) the stated max. tire pressure is actually 'low' because it is designed to let you hit potholes all day without a blowout

2) for track type performance you want *higher* than rated PSI to stiffen the sidewalls; this gives a little less patch on the pavement but greatly improves cornerning performance

3) the 44PSI rated Michelin tires on the BMW M3s we trained in were inflated to 50PSI for the course.

One thing is for sure: lower pressure means lower fuel economy (on club 'fun runs' with MPG the scoring basis you would typically blow your tires up to 60PSI or so).