Quote:
Originally Posted by Save Bluth
staying dead on the overall wheel/tire size for the XI. I am generally aware that a car (speedo) is calibrated to the wheel/tire size. But, is there a reason that the XI would be more sensitive to this?.
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This isn't just for a Xi BMW. it is for all AWD cars. you must stay within the same circumference/rotating diameter so the differentials do not suffer premature wear and failure.
The spec is different for each manufacturer. For Subaru (one of the tighter specs I believe) all four tires have to be within 2/32" circumference
IMHO, it is safest to use the OE size. If you want to switch size, stick to the same size for all (ie don't stagger) and also use the same brand for all tires. The reason for this is that tires of different brand may have different physical dimensions even if they have the same stated size, or a mathematically equivalent size