Mark Heuchert

One tire blown; How many need to be replaced?<p>One tire on my A4 Quattro is flat and unrepairable. The tires have 22k miles. I know that tires on the same axle should be replaced together.<p>But, the tire dealer claims that on Quattro's, all 4 tires need to be replaced at the same time. They claim that there is a Audi service bulletin concerning this matter.<p>Anyone have knowledge, experience or opions on this matter?

Steve S.

"dealer claims that on Quattro's, all 4 tires need to be replaced at the same time. "<p>I dunno about that one...you didn't mention what tires you have...and how the<br>wear is on each tire, but I would think you could get away with just replacing<br>the one tire ...if you had the Continentals. The SP8000s don't wear as well<br>and could be significantly different from a new tire in the tread department.<br>Again, my comments are from a non-mechanic standpoint...but I did put on<br>one new tire myself with no adverse effects...<p>Where is our new resident Audi Technician when we need him?<p>Steve S.<br>97 2.8QM

Todd W

Some tires have very tall tread blocks and the difference is quite noticeable. I would never mix really old tires and a new one on the new quattro cars. The torsen, ABS, etc. would have fits. At the minimum you have excessive driveline wear, at the worst you put the new one on the front and it handles badly.<p>That said, there are cheaper places to get tires if it is time.<p>my $0.02<p>Todd W

ChuckH

...the other tires are significantly worn, the larger diameter of the new tire will cause constantly different rotation speeds at that corner, creating extra wear on the torsen differential. Even doing them in pairs is not a good idea, apparently. If you have not rotated your tires, and the rears are like new, doing the two front ones probably wouldn't be a problem though. Personally, I would never replace one tire anyway unless the others were nearly new. I know it's expensive, but you will probably have to do the other three soon anyway, and your handling will not be flaky. <p>Charles<br>

MichaelA

A) How long can you drive around an oval road course before you destroy your drivetrain?<br>B) Why is a grossly different tire (ie, compact spare) okay? and...<br>C) What is a differential for if not to accomodate minor differences in rates of rotation?<p>I've been wrong before and I may be wrong about this, but this kind of advice sets off my BS detector. Common sense would seem to indicate that if the tires are not overly worn (ie, the rolling circumference of the old tires is not significantly different than that of the new tire) it would be reasonable to just replace the one tire. <p>BTW, I have measured the rolling circumference of sets of new tires and the variations within a set were sometimes quite surprising.<p>Mike 1.8tqms

Todd W

All of these things accumulate with time and speed. If you replace one tire at a time then it is unlikely you will ever have a matched set. That way you will drive tens of thousands of miles on an oval track!!! A differential is there to take up differences while cornering, but if it is working constantly on the highway then you will have excess wear and it will be running hotter than it is designed for. Get a hold of an engineer at Audi if you want a more detailed answer.<p>Todd W

MichaelA

Your point on the donut is well made. <p>However, since no two tires are ever the exact same rolling circumference even when new, there must be some tolerance of variation designed into the differentials. In that light, a variance of 1/2 tread depth would not seem to constitute much of a mis-match unless the new tire were unusually large to begin with. Perhaps the best answer would be to measure the rolling circumference and see if it's too much of a mis-match, but if the tolerance is zero...we're all in trouble.<p>Mike

Todd W

Not to mention tire pressure

ErikR

My donut is over an inch shorter, that is a very serious differential. The speed limit is likelier to save you from weird handling.<p>The differential is constantly turning, so I find it hard to believe it would overheat. <p>Since the f/r diffs are open, the difference in speed/torque would be taken up there. Unless a person was romping on the gas, I would assume that it would take very different front vs. rear tire sets to even engage the center diff at all. <p><br>