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      08-04-2012, 12:04 AM   #37
zzade46m3
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Quote:
Originally Posted by cmhsam View Post
Wont 21's slow down the car since you have a larger rolling diameter?
No the diameter shouldn't change, but the rolling resistance might because of weight of new wheel/tire combo. Since the factory tire is 265/40/19 F, if you do a 20" the tire aspect ratio drops by 5% to compensate for the overall diameter. So a 20" would be 255/35/20 and 21" would be 255/30/21. All keeping the OD very close to OE size. I used to be in the wheel/tire industry long ago...
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