tomkovic

SO I found a nail in my right rear tire in the middle of the tread. I take it to Big O to get it plugged and they call me to say that there is another nail in the shoulder and the tire must be replaced. Further, since my tires are half way worn ALL FOUR tires must be replaced because it is 4 wheel drive. Calling several other stores gives me the same answer. So I guess that is the deal.

My questions are:

1. Exactly what ill effects does mixing tires cause? I imagine the worn tires will have to spin a little faster since they would have smaller diameters by some small fraction than the new ones but isn't this small difference taken care of by the differentials? Or is it a front vs back speed problem? If so couldn't you just get 2 new tires and put new on the left and old on the right so front/back matched?

2. How touchy is this? Lets say I run over something a year from now when my 4 new tires are still pretty good <10,000 miles and one tire is ruined. Do I then have to get 4 new tires again?

a44me2

You do not need all 4 you are being lied to. If you have any worries replace the worn tires with the same brand and size as are already on the car.

lyleswk

Audi recommends you keep the tire diameter within 3% (I think I have this correct, but should check your manual) on all the wheels. If you exceed this, you can cause damage to the torsen unit or diffs. So, doing the math with a 235/45 17 tires like mine, you get 25.33 inches diameter (17 inch wheels and 8.3 inches of rubber). 3% of that is .75 inches which I believe is about the max wear of the tread if not more. So, if you have one tire that is brand new and the other 3 are at the limit of their tread, you might have an issue, but then I would go ahead and buy 4 tires if this is the case. If you have somehting like 50% wear on the tires and put on new one on, I doubt you exceed the calcs above.

So, I'm with A44me and buy just one of the same brand and size tires that you have and you shouldn't have a problem. If you mix brands, I would simply measure and do the math.

jordonb

I agree with the previous 2 posts. as long as the other 3 are not bald (or down to the last 20%) i would just buy the one tire. should be WELL within tolerances.