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      08-15-2015, 03:15 PM   #1
DeutschRennfahrer
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Replaced rear tire - will uneven tread depth hurt my LSD?

I recently had to replace my right side rear tire due an unrepairable leak caused by some nails. I replaced it with a brand new tire. My concern is that the uneven tread wear between the brand new tire on the right and the one on the left with 75% wear might put extra stress on the differential. Is this true? Should I move the new tire to the front instead?

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      08-15-2015, 04:56 PM   #2
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Noob here but I think the only E85/86 with rear LSD from the factory is the M.
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      08-15-2015, 05:39 PM   #3
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I don't know if it will cause problems or not but I think it's just good practice to replace fronts/rears as a pair. I had the same thing happen to my ZHP last week. Sucks to spend $500 on something I didn't need earlier in the day but oh well.
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      08-17-2015, 02:33 PM   #4
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With the difference in diameters between the old and new tire. It does make the diff work a bit more, but unless you have an M with the LSD you should probably be OK. I'd go ahead and replace the 75% worn tire now anyway just to get the wear out synched up again. Otherwise, you'll continuously have one new and one worn tire.
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      08-17-2015, 02:40 PM   #5
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Don't some tire shops shave the new tire for you to match the old one? I'd ask about this first because it might be cheaper especially if you don't drive that much.
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      08-17-2015, 09:31 PM   #6
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Quote:
Originally Posted by Twixboy View Post
Don't some tire shops shave the new tire for you to match the old one? I'd ask about this first because it might be cheaper especially if you don't drive that much.
You can't be serious
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      08-17-2015, 09:48 PM   #7
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A race shop could shave the tire, although i have never seen this done for this reason.
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      08-17-2015, 11:47 PM   #8
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I had the same thing happen on my ///M with about 7900 miles on the tires.
Tread depth difference was slight, but noticeable.
I had the same concern. I just tried to light the right side up more than the left to even them out.
Put 22,500 miles on them before replacing both.
Diff still works.
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      08-18-2015, 08:24 AM   #9
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Quote:
Originally Posted by Daemonblitz View Post
You can't be serious
I'm serious. I've had a tire shaved prior to shipping from Tire Rack before. It might not be a big deal on our cars, but it's more common to do this on AWD cars where it's more important to have 4 matching tires. I opted to buy and shave 1 tire rather than buy 4 new ones.
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      08-18-2015, 12:01 PM   #10
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Quote:
Originally Posted by Twixboy View Post
I'm serious. I've had a tire shaved prior to shipping from Tire Rack before. It might not be a big deal on our cars, but it's more common to do this on AWD cars where it's more important to have 4 matching tires. I opted to buy and shave 1 tire rather than buy 4 new ones.
Yabut his other tire is 75% worn (I managed to miss that too the first time). It would be more economically practical to get 2 new tires.
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      08-18-2015, 01:09 PM   #11
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Quote:
Originally Posted by wdb View Post
Yabut his other tire is 75% worn (I managed to miss that too the first time). It would be more economically practical to get 2 new tires.
My bad, I read the original post as 75% tread left. That's the only reason I brought up tire shaving.
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      08-18-2015, 05:20 PM   #12
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I never bought into the AWD needing four exactly worn tires either. The number of people that don't rotate their tires, buy mismatched brands at different times, etc. would have the huge numbers of AWD cars all with problems. Then, put on a space saver spare where there is almost no chance of it being within 32nds of matching the rest of the tires and it would also destroy diffs quickly. My guess is some of the space savers are off by a huge amount, many times greater than the new to worn tire question.

While I don't think it will hurt you diff I would replace it. Normal tire comes with about 12/32" of tread, if you are saying the worn tire has 25% left, 4/32", it is worn enough to not deal with.
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      08-18-2015, 07:47 PM   #13
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Quote:
Originally Posted by David70 View Post
I never bought into the AWD needing four exactly worn tires either.
Just went through this with my Daughter's Subaru.
She took it to Americas Tire with a slow leak.
They told her there were 3 nails in the tire and it couldn't be fixed.
And because it was AWD, she would need 4 new ones.

She took it to the dealer, and they said it had one nail and then fixed it for free.
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      08-19-2015, 08:52 AM   #14
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Note to self: America's Tire sucks.

AWD cars absolutely are sensitive to tire circumference. Center diffs may be a viscous coupling and can overheat if the front/rear difference is too great. L/R difference can be less of a hassle if there is an open diff but obviously LSD will have issues if it has to constantly compensate. I'm not well versed in electronic versions that use the brakes to fake a LSD so I can't tell you what might happen with them.
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      08-19-2015, 12:09 PM   #15
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I'd be more concerned with the traction on the older tire / rubber (25% left if I'm reading correctly) than the diff, and how that would affect performance and handling. Any reason not to go with fresh rubber on both sides?
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      09-07-2015, 08:04 PM   #16
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RE: the AWD/tire OD discussion, I've heard that putting a significantly mismatching OD on an AWD xDrive Bimmer can cause the car to go into limp mode in order to prevent diff wear.

So it's confirmed the non-M cars do indeed have a mechanical diff? OP, if this is the case and if you only have 25% tire tread left, I would recommend purchasing an additional new rear tire and chalk it up to bad luck - better safe than sorry.
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      09-07-2015, 08:07 PM   #17
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Quote:
Originally Posted by wdb View Post
Note to self: America's Tire sucks.

AWD cars absolutely are sensitive to tire circumference. Center diffs may be a viscous coupling and can overheat if the front/rear difference is too great. L/R difference can be less of a hassle if there is an open diff but obviously LSD will have issues if it has to constantly compensate. I'm not well versed in electronic versions that use the brakes to fake a LSD so I can't tell you what might happen with them.
So what is the amount that matters? If you don't rotate your tires religiously and get uneven tire wear you will ruin the center diff? I have a hard time believing all of the Subaru owners are making sure they rotate their tires exactly when needed.

Then, what happens when you put on the space saver that can't match exactly (new or worn tires)?
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