akingzkid

So, I have a weird random situation. I decided to replace only 2 tires on my 06 A6 3.2 Quattro. Why would I do something like that you ask? Well, because the front were worn pretty badly around the outer edges and the back still looked pretty good. So I kept the back tires and moved them to the front. I put the 2 new tires on the back. The 2 new tires are the same manufacturer and size as the old tires.

I'm not sure how many miles are on them. They were on the car when I got it 5.5 months ago. That's probably not even relevant.

The shop that I had mount them advised me that on AWD vehicles it is best to replace all 4 tires at once and had me sign a waiver because the difference in thread depth between the my front tires (old tires) and my rear tires (new tires) was greater than their threshold of 2/32. Meaning, you measure the tread depth of the old tire (and get 2/32 for example) and you do the same for the new tire (and they are 7/32 for example). The difference would be 5/32 which would be greater than their allowable limit of 2/32. They said mine were a 3/32 difference.

I have done some research on this topic and found all sorts of answers. Of course the most common sense thing to do is replace all 4 tires. I get that point but please humor me here.

During my research I have found that the max difference should be 2/32 or up to 3/32.........or up to 1/2 inch difference in the tires circumference when you compare the circumferences of the new and old tires. The circumferences have to be done with the tires off of the rim since the amount of air in the tires effects the circumference measurement. Well, I'm not taking the tires off the rims to measure them so I have to use this tread depth gauge that I have. I read on another site that says that they (the site) are really familiar with Suburus and Audi quattros. They say that Suburus have the lowest tolerance; 2/32 of a difference and if it is more than that, you WILL ruin the suburu transmission. That site says that Audi quattros can be up to 4/32 difference. My car's owner's manual does not give any specific measurements but it does say that if you have to replace less than 4 tires that you should replace them in pairs (to replace 2, not 1 or 3) of the same brand and size.

So, for piece of mind I decided to do some measurement of my own. The back tires, being that they are new, have 7/32 or 8/32 of tread depth depending on where you measure them. I am getting 7/32 when I measure between the outermost tread and the 2nd tread (the one next to it). But if I measure between the 2 innermost treads I am getting 8/32.

The fronts (old tires) are consistently measuring 4/32.

So, that is a difference of 3/32 at best or 4/32 at worst.

I know most replies to this will be, "Just go and buy 2 more tires dude. Buying 2 more tires will be far less expensive than a new transmission". Again, I know that's the obvious answer but I want to know if I no kidding, really need to do that. And if I don't , I am not going to.

Again, the tires that I moved to the front (from the back) have good tread on them (4/32) and I have a hard time throwing them out. But I don't want to ruin my transmission.

Your thoughts???

Thanks.

LarryJa

I replace 2 tires each year, in the Fall.
The new ones go on the front.
The next best two go on the rear. Then the best remaining one is my spare.
Of course, I am careful to get the same tire brand, size & model each time.
So, I'm careful to select the best tire for me whenever I get a different car &, then, stay with it.
I presently have Continental DWS-06's.
This way, I have my best tread on the front wheels through the Winter.

raj99

Topic has been discussed a few times on the forum, if you open the owner's manual you'll find "rolling radius of all 4 tires must remain the same or within 4/32-inch of each other in remaining tread depth. " It's not the tranny that should be the major concern, but the quattro system - the differential, which will prematurely fail.

Our cars are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.

akingzkid

ok. However, if you are doing it consistently each year, then I doubt you have that much of a difference in tread depth from old tires to new tires since it has only been a year.

Any thoughts on my concern? I'm fine where it is or should I buy 2 more new tires? Thanks.

akingzkid

Raj,
Thanks for the reply. I didn't see that in my manual. Probably because I didn't look in the right section. So, if that's the case, then the website that I was looking at knew what they were talking about. Glad to hear it's the diff that would go out as opposed to the tranny. Diff is easier and cheaper to replace (although I don't want to ruin either of them).

So do you think I am ok as is? Or spring for 2 more tires? Thanks.

raj99

I wouldn't but that's me..I think 4/32" is too far a gap and would stick with 2/32", since binding the diff and causing excessive wear ain't that great. If you rotate tires, you won't have too much delta between your front and rears, so you only need to change them all at once vs. the 2 at a time. Also, I've found that sale of 4 tires tend to be better than 2 tires.

KevinGary

jeffpuxx

I would bite the bullet and go with 4 new tires.

In the grand scheme of things you are not spending that much extra money especially given that there are some great options out there that have long tread life.

UCLABB

akingzkid

Too late to look for options. I already got 2 tires. Now I would have to buy two more of the same. I could have gotten a $50 mail in rebate if I had gotten all 4 at once. I should call them to see if they will make exception and still let me get that even though I would be buying 2 and then 2 more separately. Thanks.