[EasternLI]

Quick question, looking at a set of winter tires for my 21” M sport wheels however the set is 285/40 21 and 315/40 21 which is a bit taller in the rear then the stock 35 height tires, will this affect anything adversely ? Don’t care if my mph is off a tiny bit just don’t want to screw up some other system on the vehicle

TIA

[GlennC]

Originally Posted by EasternLI

Quick question, looking at a set of winter tires for my 21” M sport wheels however the set is 285/40 21 and 315/40 21 which is a bit taller in the rear then the stock 35 height tires, will this affect anything adversely ? Don’t care if my mph is off a tiny bit just don’t want to screw up some other system on the vehicle

TIA

This should not be a problem as the diameter difference between front and rear will be 1.9%.

[LexxM3]

Originally Posted by GlennC

This should not be a problem as the diameter difference between front and rear will be 1.9%.

No. The real answer is nowhere near that clearcut on an xDrive, an AWD system. A good rule for AWD with no other knowledge is that the diameter (and, equivalently, the rolling circumference) of all 4 tires should be the same; width can vary, diameter should not. If you want to violate that rule of thumb, the situation is open to variables and interpretation and I don't believe anyone really knows (at all or yet) whether some variance between front and rear diameter on the Gxxx xDrive is a problem or not. If there is a problem, it is related to AWD differential being non-neutrally biased for extended periods of time during normal, primarily straight-line driving.

Lots of articles out there. The Subaru issue always mentioned is a classic — no variance allowed at all and documented severe damage. Gxxx xDrive — unknown at any detail. A few random ones on a quick search:

https://m.tirerack.com/tires/tiretec....jsp?techid=18

https://www.souzastireservice.com/Ti...tching-AWD-4WD

https://www.fitmentindustries.com/bl...aggered-on-awd

And by the way, the diameter difference is 3.2%, not 1.9%.

[GlennC]

Originally Posted by LexxM3

No. The real answer is nowhere near that clearcut on an xDrive, an AWD system. A good rule for AWD with no other knowledge is that the diameter (and, equivalently, the rolling circumference) of all 4 tires should be the same; width can vary, diameter should not. If you want to violate that rule of thumb, the situation is open to variables and interpretation and I don't believe anyone really knows (at all or yet) whether some variance between front and rear diameter on the Gxxx xDrive is a problem or not. If there is a problem, it is related to AWD differential being non-neutrally biased for extended periods of time during normal, primarily straight-line driving.

Lots of articles out there. The Subaru issue always mentioned is a classic — no variance allowed at all and documented severe damage. Gxxx xDrive — unknown at any detail. A few random ones on a quick search:

https://m.tirerack.com/tires/tiretec....jsp?techid=18

https://www.souzastireservice.com/Ti...tching-AWD-4WD

https://www.fitmentindustries.com/bl...aggered-on-awd

And by the way, the diameter difference is 3.2%, not 1.9%.

I stand corrected. Thank you