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[gpitts]

My first original post, so please go easy on me.

I experienced the differential "clunk" issue in my E92 M3. After about 8K miles, I took the car in and got the usual repair of a different differential oil and the twenty circles in each direction. Problem solved.

One evening (at about 13K miles) I had a flat driver's side rear tire. Fortunately the TPMS flagged it just as I was leaving the driveway, so I had not gotten far. Since I just had surgery about a week prior (and was not supposed to be driving, ahem), I just used BMW Assist and they sent a truck to take the car into the dealer. I knew I was looking at a tire repair at a minimum, but the dealer called me back the next day and told me the flat tire was not repairable and needed to be replaced. He then cautioned me that the right-rear tire should be replaced as well, since the tread was down to 1.5 mm. I honestly don't know why I even asked, but he indicated that the flat tire was at 4 mm. Huh? I do not track my car, and I do not drive it hard at all. So I am hard pressed to explain this degree of difference in wear between the two rear tires.

My question is whether you think this degree of difference in wear on the rear tires is normal, and if not whether you think this could be related to the diff issue?

[roastbeef]

the m3 diff has the ability to limit slip, and completely lock. a tight lsd or locked rear diff can absolutely lead to fast tire wear, since the tires spin at different speeds when cornering.
i don't know if driving the car in a comfort or sport mode tightens up the rear diff, or if it only uses the lsd/locking action in m dynamic mode.

[jbaier@tms]

It seems a bit extreme but slight differentiated tire wear is normal. Not all four tires on a car are going to wear exactly the same. There are many factors that go into tire wear. The same goes for brake pads, we take brake pads off of 20K E90 M3s all the time and a lot of the time there is some difference between the pad thickness between the right and left side pads with the same mileage.

Its hard to say without knowing the car or your driving behavior but if there was a problem with the diff that would create that much difference. It could be the tires themselves, there may be some malfunction or manufacturer issue with them, tire pressures may have been different, alignment could be slightly off, etc.

Where did they measure the tires tread? Negative camber in the rear of an M3 obviously would make the insides of the tires wear quicker than the outsides, especially when street driving. If the car drives and performs normal I would chuck it up to the dealership exaggerating the difference and measuring in different areas of the tire. I would not put it past them to exaggerate it so you would purchase two new tires, which you should really do no matter what.

[gpitts]

Originally Posted by jbaier@tms

It seems a bit extreme but slight differentiated tire wear is normal. Not all four tires on a car are going to wear exactly the same. There are many factors that go into tire wear. The same goes for brake pads, we take brake pads off of 20K E90 M3s all the time and a lot of the time there is some difference between the pad thickness between the right and left side pads with the same mileage.

Its hard to say without knowing the car or your driving behavior but if there was a problem with the diff that would create that much difference. It could be the tires themselves, there may be some malfunction or manufacturer issue with them, tire pressures may have been different, alignment could be slightly off, etc.

Where did they measure the tires tread? Negative camber in the rear of an M3 obviously would make the insides of the tires wear quicker than the outsides, especially when street driving. If the car drives and performs normal I would chuck it up to the dealership exaggerating the difference and measuring in different areas of the tire. I would not put it past them to exaggerate it so you would purchase two new tires, which you should really do no matter what.

Thanks for the reply! I agree that tires will wear differently, no issues there at all. My concern was on the degree of difference in the wear. This is my daily driver, so my driving style is pretty conservative. The TPMS in these cars is pretty sensitive, and other than my flat tire, I've yet to see it come on on my car. Also, my diff still "clunks" from time to time - although not in any consistent pattern that would allow me to take it to the dealer and have them reproduce it there - so I'm wondering if this is another argument to use that the diff is not yet right and really needs to be replaced.

The Contis that came on the car start with 10/32" (about 8 mm) of tread, so a difference of 20 percent wear on the tires felt greater than what I would have expected. You may be right about the dealer nudging me in the direction of replacing both, which I would have done either way given the relatively low tread life remaining on the "good" tire.

[gpitts]

Originally Posted by roastbeef

the m3 diff has the ability to limit slip, and completely lock. a tight lsd or locked rear diff can absolutely lead to fast tire wear, since the tires spin at different speeds when cornering.
i don't know if driving the car in a comfort or sport mode tightens up the rear diff, or if it only uses the lsd/locking action in m dynamic mode.

Thanks! I'm thinking the diff probably contributed to the difference in tire wear as well. I think I'll pay my service advisor another visit Monday.

[roastbeef]

like i said, i don't know if a more aggressive transmission setting effects the way the M differential works, but spirited driving and driving in M dynamic mode will certainly result in a tighter rear diff, which will reduce tire life.