R3Wood

Good question. I have no idea, but I was thinking maybe tire wear? I saw online, somewhere, a person purchased a 2011 and saw the increase from the '05, 06, etc. I still don't know this to be true, but I may go by the dealer today and look at a 2011 and see what the rec. pressure may be.

The G Man

I own a 2011 A6, its around 40 PSI, same tire, same car, but different tire pressure. I wonder why.

R3Wood

GMan, if you look on your fuel filler door, what does it say for the 2011, for normal load tire pressure front and rear? My 2005 says normal load, 33 rear and 36 front for 18" 97H's.

irenesbob

On my 2010 the 245/40x18's are XL (extra load) - maybe the 2005 18" tire was not XL. This could matter.

R3Wood

Bob, same tire on the '05. 245/40R18 97H XL.

R3Wood

New rubber is on. I just went with "max" load ratings, 42PSI rear and 38PSI front. It feels pretty good. Got on the Garden State Parkway and went up to 95MPH, smooth.

The_Mizarc

The sticker inside my door reads 39 front 42 rear.

R3Wood

THANKS!

R3Wood

P.S. They gave me free Nitrogen in the tires, but I don't feel much difference. I would not have paid for the Nitrogen, but since it was free, I decided to give it a try. 42PSI in the rear feels a little stiff.......

TVR1977

I wouldn't use the "max load" pressures given. If you look at the pictograms near the tire pressures, you'll see that those pressures are recommended for increased load in the rear of the car.

With tires, there is an "effective radius" to the wheel/tire caused by the flattening of the bottom of the tire under load. (i.e., the "effective radius" is the distance from the hub center to the ground when the wheel is under load).

Tire pressure changes can be viewed in terms of contact patch as well. If the tires are "flattened" to the same degree at front and rear, the contact patches will be the same size.

You really want the effective radius and the contact patches to be the same at all four corners. That is why most recommended pressures are higher in the front (where the weight is).

On an AWD car, this is even more important, because it will affect how torque gets put down to the pavement.

If the pressures are not properly adjusted for load, neither the contact patches nor the effective radii will be equal. The different radii result in different torque applied, and the different sized contact patches will affect the traction available at each corner.

I'm sure all the Audi electronics can compensate for this, but I had a Subaru (much simpler technology) that was very sensitive to this. One time I did my brakes, and while I had the car jacked up I decided to rotate the tires from front to rear on each side. I neglected, however, to adjust the tire pressures. I ended up,then, with a higher pressure in the rear (the lighter end of the car).

Next highway trip it rained, and with even moderate acceleration at highway speeds, the car fishtailed pretty alarmingly. Correcting the tire pressure differential front to rear solved the problem.

The "Max Load" recommended pressures are designed to compensate for rear seat passengers and a trunk full of their luggage. For regular daily driving
- say, front passengers only, no luggage - you should use the standard recommended pressures, which are generally 2-3 lbs higher in front than in rear.

Just my $.02.