ADAMB

The tire are about 30-40% warn and the book, if I understand it correctly, says to replace all 4. I just got 18's and this is going to cost me $800 in tires no counting delivery or installation...

Do I need to replace all 4 or am I just worring too much?

knh

I replaced one tire on my 96 Outback (AWD) at 20,000 miles without problem. Subaru had a similar warning. The Subaru service dept told me not to worry, and everything was fine.

Haven't had that problem with the A4 yet, though.

Mark Collett

I work for Michelin, and being there, I hear alot about tire stories. Something relatively new has been happening to 4WD SUV's and could happen to the A4 also. It's where an individual must replace one tire (maybe it's flat) and replaces with the same size, but different manufacturer.
A week or two later (maybe a month) the person comes back to the shop saying that there is $3000 worth of damage to their drivetrain, and the dealer says it's the tire shop's fault. What's going on?

You may notice that tires of the same size from different manufacturers (or the same, but different lines) will look different. For example, a 205/55R16 Michelin will 90% of the time have a different overall diameter and width than a 205/55R16 Dunlop. This is just from allowable deviations that shouldn't be so, but that's a different story.

The problem with modern, precise AWD setups is that minor differences in the circumference of two tires is destroying the internals. In the case above, the new tire was almost an inch bigger than the others on the vehicle. This makes the internal differentials (the A4 has 3 right) think there is always a slippage at one of the wheels, and overheat trying to transfer torque to the "non-slipping" wheels.

What I am saying here is if you were to replace the one tire with another, it could destroy the Quattro system.

So how do you keep this from happening?

You could mount the same tire (the EXACT same tire, but new obviously) in place of the old one, and it should probably work. Here's a rule of thumb though:

Mount the new tire, and compare the OVERALL CIRCUMFERENCE to one of the older, mounted tire. Do NOT compare unmounted tires. Mounted and inflated tires will differ greatly in dimensions to their unmounted dimensions. Use a tape measure, and try to be accurate. If the difference in diameter is about 1-2%, you should be okay. HOWEVER, I do not claim full responsibility for this information, its only my best guess based on other information I have read. If you'd like more info I can track down the article and find where it came from.

Here's another idea. The A4 comes with a full spare, right? At least the new ones? The engineers must figure that someone could have to mount that spare (at full tread depth) on a car with tires that barely pass DOT inspection. Given that this safety factor probably exists, you could just replace the bad tire with an EXACT same new tire and be done with it. Again, only a guess.

Mark Collett

JMorrison

tire sizes or types. Not even different tire types (tread pattern/compound) in the same size from the same manufacturer. I'd say get the exact same tire brand/type/size that's on there now and go for it. My $.02, IMHO, your mileage may vary.