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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?

mac
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7 Answers7

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"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...

Brian Knoblauch
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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.

Drake Clarris
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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.

mckenzm
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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.

Bryce Hove
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I think the best advice is just to follow the vehicle manufacturer’s guidelines. I have read that there’s a 2/32 tolerance between tread depths on all 4 tires, but once you’re outside of that there’s a risk to damaging the drivetrain. I’m sure there’s some jack-wagon out there who has taken the risk all because they felt a salesperson was just trying to “sell them” and it panned out for them luckily. Now obviously temporary spare tire usage is allowable as it isn’t long term, but I would just say do all 4 if at all possible. It does suck when you damage one tire and have to replace all 4 (usually). I’d say that’s the cost to wear the AWD/4WD badge that 60% of the population doesn’t need anyway, but you were talked into by your salesperson at the dealership. ;)

RaodRunner25
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the overall diameter should be: 17"rim = 431.8mm;
tire section height = 255 x 0.55 = 140.25 mm;
Overall diameter = 431.8 + 140.25 x 2 = 712.3 mm

randall
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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!

Oliver Buchmann
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