1999Audi

one tire is almost bald(rear pass.) and the other three are in decent shape
What could cause this?

I usually check tire pressure every 3 months
130k miles
99.5 2.8 V6 QUATTRO

tr3ndsetr

I had a similar issue. In my case it was the alignment. Driver side kept balding on the inside of the tire. Unless you looked underneath, it was almost unnoticeable. I replaced the tire 2x. Finally a mechanic pointed it out. Got the alignment at Pepboys for less than $100. Issue went away.

uberwgn

I'm going to suggest it's something to do with the design of the drivetrain. I've experienced the exact same thing on my A4 car...that right tire showed significantly more wear than the other corners of the car.

In my case it was not related to alignment. I have the alignment check annually and it's as close to perfection as anyone could hope for.

Checking tire pressures every 3 months is not a good strategy. We need to put you on a plan where you check it every other week

twentysevenlitres

Not just an alignment, get a 4 wheel alignment.
Rears on B5 Quattros have a nice little eccentric washer controlling camber, if its out on one side it could scrub the tyre out pretty quick...

1999Audi

4 wheel alignment done every 10month (I have Firestone Lifetime alignment) + they know about eccentric washer controlling camber (print out was provided)

4wheel alignment was done in jan2014

twentysevenlitres

Then my only other suggestion is that you may have worn suspension bushes or shock absorber...

1999Audi

4 New OEM shocks installed - 104k nov/2011, Now 130k miles

David.Norton

Sounds like you have done your homework and gotten to the obvious stuff, perhaps it could be something like a dragging rear brake? With the integrated handbrake they sometimes like to do that. I had one stick on once just enough that you could see the rotor glow at night, and smell it was hot, but the car didn't handle any differently.

1999Audi

no my rotors does not glow at night and no smell.

could it be springs? ... like one worn more than the other?