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Old 12-16-2012, 04:13 PM   #21
lmr2wil
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Join Date: Oct 2010
Location: MI
Posts: 508
My Ride: '00 328Ci
Quote:
Originally Posted by sunsetcoast View Post
The difference in diameter is 5%, but the sidewall height differential is actually closer to 8%. The nominal sidewall heights:
  • 225/45 (standard size) = 101 mm
  • 245/45 (optional rear size) = 110 mm
  • 215/55 = 118 mm
8 mm is about 1/3".

Tread depth of a typical tire is 12/32". So the difference between a new and a worn tire (say mounting a "new" spare for a worn one) is 10/32" (or 8 mm). The DSC system would be expected to deal with this.
I don't disagree with your math... but I do disagree with the optional rear tire size. I was under the impression that the rear "wide" tire option was 245/40/17 (per the owners manual). This has a sidewall of 98mm. BMW has kept all the sizes very close in diameter (I believe for a reason).

Luke
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