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      02-17-2012, 12:58 PM   #1
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new wheel/tires - adjust speedometer?

My first purchase was to upgrade from the 18's to genuine OEM ZCP 19's. Do I need to make any adjustments after moving up in size (speedometer, etc.)? Does it depend more on tire size? My new tires are PSS XL - 245/35ZR on front, 265/35ZR on back.
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      02-17-2012, 03:44 PM   #2
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Those are stock size, no need to adjust anything (not that you could adjust the speedo if you wanted to...)
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      02-18-2012, 09:57 AM   #3
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As long as the total diameter of the wheel and tire together is the same (it is in this case) nothing changes on the speedo. The speedometer is often off by several percent from the factory, so even if you have small changes in tire size most people don't worry about it.

Generally, a difference of 3% or less in rolling diameter is considered negligible.

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      02-18-2012, 12:02 PM   #4
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If you have a smart phone with a GPS application, you can measure your true road speed vs the speedometer output while you are on the highway sometime.
Allows you to know the true offset.

Stock wheels and tires often 4% high in speedometer reading in US for M3.
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