So the other day i found an air bubble in the sidewall of one of the rear tires on my wifes 04 a4 quattro. Now I know I should probably replace all 4 tires since these ones have been on the car for a few years but we just got married a couple weeks ago so money is kinda tight right now. So my question is, will I damage anything by replacing only the fronts and having half worn tires on the rear?

 

Yes, preferably on the same axle. Unlike some other AWD systems out there, you won't risk damage to Audi's rock-solid Torsen diff by doing so.

UberTeile

 

Right on UberTeile!

Audi recommends making sure that all of the tires are within 4/32'' of each other and with this in mind you can match on the same axle without detrimental results to the drivetrain.

If you have a few minutes, check out this article: http://www.tirerack.com/a.jsp?a=BY4&....jsp?techid=18

 

4/32, isn't that 1/8"?

 

^^MATHaholic^^

Yep, but, 4/32 is 4x as precise!

To the OP:

Yes, you can replace only two, IF they're both front, or rear. But, It's generally not recommended, especially if, as you say, they tires have been on the car for a while. It's wifey's car and do you REALLY wanna play around with safety and potential mechanical problems on the wife's car like that? Take it from an old guy, don't risk anything you don't absolutely have to. If that tire fails at speed, nothing good could happen without divine intervention. If you replace only the front or rear pair, given the age of those tires, and it stresses the middle diff to the point of failure, again, at speed, it won't be pretty.

Do the right thing... Even if it hurts for the moment. Replace all 4 with something you can afford, and laugh about it, years and years from now, while you're sharing stories with your grand-kids.

 

It's also 8/64! Even MORE precise

In the tire biz we refer to tread heights in 32's. It's just easier to pick one standard depth than to figure out different fractions all the time.