Here are a couple formulas for figuring out offset and backspacing.
Let's use the SVT Contour wheel for example.
We know that the wheel is 6.5 inches wide. So we start by dividing that number in half to get to the center of the wheel, and then adding a half-inch to accomodate for wheel lip. We've now got a total of 3.75 inches. Knowing that the backspacing on this wheel is 5.69 inches, we can get an easy approximation using this formula:
5.69 (backspacing) - 3.75 = 1.94
1.94 x 25.4 (conversion to millimeters) = 49.276
So we know that the approximate offset on this wheel is 49mm millimeters.
To calculate backspacing you use this formula:
(rim width ) / 2 + 0.5 + (offset /25.4) = backspacking
So for a SVT Contour Wheel:
6.5/ 2 + 0.5 + (49.276/ 25.4) = 5.69"
-Mark
