On a 2004 VW R32 (which uses a Haldex AWD system), I have one damaged summer tire. All the tires have at least half of their usable tread depth left. At $200 ea, I'd like to replace only a pair of tires, which I'd mount on the front of the vehicle where the wear occurs more quickly.

A TireRack salesman said that some AWD vehicles have a tolerance of 2-3/32" tread difference between axles to avoid damage to the transfer case (his term, i'd call the component in question a center differential), and that I should check with VW before buying the new tires.

VW customer care gave the answer that as long as the two tires new tires are either both on the front or both on the rear, that it's OK. In other words, there's no tolerance limit. I find this somewhat hard to believe. A VW dealer I called gave the off-hand answer of 6/32".

Would having tires of different size on the front and rear axles put extra stress on the center differential of an all wheel drive car?

  • I'll mark my own possible dupe, but there's some subtle (or not-so-subtle) differences between the conditions here – mac Nov 27 '12 at 19:49
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    I have always wondered if they will replace all four tires if you made a "roadhazard" replacement claim for one tire and the tread difference between the new and old exceeded 2/32". – mikes Nov 27 '12 at 22:06
  • @mikes - I asked about that when the tire shop tried to sell me the road hazard insurance. They only replace the failed tire. I've heard that some shops have some kind of tire lathe that they can use to shave down new tires to match old ones, but I've never seen a shop that actually has such a thing. – Johnny Mar 26 '14 at 23:51
  • @Johnny re: tire lathe, this is actually what I ended up doing in this case. TireRack shaved the tire for me at no charge--they just asked what tread depth I wanted on the shaved tire. – mac May 13 '15 at 21:36

"It depends"... I've historically opted to replace all 4 just to be safe (on my AWD with 3 LSD beast, on the RWD open diff I replace 1 at a time if needed :-) ). In theory a small difference won't blow up the transfer case or the diffs (there's always at least a TINY difference anyways). Normal wear with a normal rotation obviously doesn't violate the limit, but 2 brand new tires with 2 at the wear bars supposedly does. Where exactly the line between "safe" and "unsafe" is, I have no idea. Actually, it's probably more of a gray area based on heat buildup...

  • Anecdotally, another issue - a couple of years back I just got new fronts, and my Subaru got incredibly tail happy. Part of it would be down to the reduced grip at the back end, but part would be because of the extra torque being transmitted to the smaller radius rears. I replaced the rears a week later after ending up pointing the wrong way on a roundabout by accident! – Rory Alsop Nov 28 '12 at 9:14
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    @RoryAlsop That probably happened because your mis-matched tire sizes caused the center diff to slip, overheat, and bind. That will quickly cause permanent damage to the viscous coupling, and will result in all kinds of wonky handling (unless you're on dirt, where it's just more awesome). For auto trans equipped Subarus the effect is similar, because the AWD system will engage the center diff clutch. – Steven T. Snyder Aug 28 '13 at 21:10
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    For reference, Subaru's permitted difference in tire circumference is 1/4" between the smallest and largest tire. That ends up being between 1/32" to 2/32" difference in tread depth (tire radius). Not much. I don't have any specs from other manufacturers. – Steven T. Snyder Aug 28 '13 at 21:13
  • Series - hadn't thought of that. I was embarrassed to have spun but assumed it was entirely me messing up. Reassuring to think it may have been exacerbated by a hardware issue:-) – Rory Alsop Aug 28 '13 at 21:19

Just as a note, awd systems I worked on in the past had a limit of 1 inch difference in circumference of any tire to avoid abnormal wear of the transfer case. And I did see several cases where the chain the case was already stretched with a bad jerking on take off, and new tires fixed the symptom although of course the underlying cause remained.


Yes, and often the wear patterns are noticeably different front to rear. If you do not rotate, you can replace in pairs. Most people will replace a whole set just for the convenience. The front tires will generally wear more, because they are steering and their alignment will vary subtly depending upon load. If you have toe in or toe out issues they will wear a lot more quickly, and if you drive at high speed also. AWD is fairly all encompassing, the drive and suspension also matters. Some AWD do not distribute torque equally front to rear either. The center diff should cope unless they are actually different sizes, and if you are replacing front or rear then the diffence in diameter before and after will be small and not far off the difference you already have.


I just bought a 2018 A4 Allroad and one of the front tires received a non repairable puncture. According to page 332 of my owner's manual, Audi recommends replacing at least the two tires on the same axle but does not suggest replacing all 4 tires unless all 4 tires are worn to their limits.

  • welcome, thanks for providing sources for your answer. and also, nice choice on the new car! – mac Jan 16 '19 at 17:13

This has been an ongoing debate forever - and I believe the “replace all 4” mantra is being driven by the tire manufacturers and the the tire dealers. Here’s my semi-educated theory: Most manufacturer’s state for their AWD vehicles the circumference of all 4 tires must be within 1%. That DOES NOT mean a difference of 1% in tread wear. On my xDrive BMW running 255/55/17 the circumference of a new tire is 711mm. Assuming no other tires wear, the circumference of one tire would have to drop by 7.1 mm in order to result in a 1% drop. So, let’s think this through. A 7.1 mm drop would be a 3.55 mm drop on either side of the tire tread. A typical brand new tire has 10/32 of tread, or 7.94 mm. In order to get a 3.55 mm reduction, your tire would need to be about 50% worn out. So let’s say you have one damaged tire, and the other 3 still have >50% tread life? Less than 1% difference and you’re good to go. Don’t let them sweet talk you into 4 new tires!

  • So, it was a different fault that caused the Volvos to have issues with the 4 wheel drive system due to tire wear. I think the manufacturer has more experience... – Solar Mike Jan 31 '20 at 10:13
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    You're confusing circumference with radius in your calculation - 7.1mm drop in circumference is a 2.261mm drop in diameter and so 1.13mm drop in tread depth, or about 1/7 of the tread depth – Nick C Jan 31 '20 at 10:48

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