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      09-28-2009, 06:29 PM   #14
elp_jc
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Quote:
Originally Posted by RGuard250 View Post
So would 255/35/19 in the front and 275/30/19 in the rear be good?
As you read on the many threads after mine, math can't predict if tires would rub or not. That depends on wheel size and offset. Oh, and math depends on wheel width too, as if you cram a tire in a too narrow wheel it'd be taller than the math suggests.

Now to the math. A 265/35/19 tire has 82.634" of circumference. You need circumference to calculate speedometer error. But for clearance, you need RADIUS. It gets simpler here. Every 10mm larger width (275 vs 265, etc) with equal aspect ratio, increases radius by 3.5mm (10mm * 35%). So any size above stock with the same 35% aspect ratio will reduce fender gap by 3.5mm by every 10mm of added width, so tire would look even bigger than stock, and car would travel faster than with stock tires. But if you only go +1 in width (275/35 vs 265/35), you're talking a 1.04% increase in circumference (and 3.5mm less fender gap), which equals 79.2 mph speedo vs 80 real (IF it was accurate ). Hardly anything.

If you go to 30 series, the 305/30 is virtually identical to stock, so anything in-between will be smaller. The next size larger than stock, 275/30, has 3.17% less circumference (82.5 mph speedo vs 80 real, plus factory error ), and is 10.25mm smaller in radius (added fender gap). The 285/30 would add 7.25mm of fender gap; 295/30 4.25mm and 305/30 1.25mm (almost like stock). Hope this helps.