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Old 12-16-2012, 04:54 PM   #19
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Join Date: Oct 2007
Location: SW Michigan
Posts: 802
My Ride: '99 323i & '00 323iT
Originally Posted by lmr2wil View Post
The bigger question is diameter (get that wrong and the DSC won't let you live it down). The 215s are 5% larger in diameter than the 225's. This is likely enough to cause the DSC to think there is a malfunction
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.
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