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Equations
 
RPM = (336/Tire Diameter) x MPH x Gear Ratio x Overdrive Ratio

MPH = (TireDiameter x RPM) / (336 x Gear Ratio x Overdirve Ratio)

Gear Ratio = (TireDiameter x RPM) / (336 x MPH x Overdrive Ratio)

Axle Load (lb.) = GVWR x .75

*note* Assume that as much as 75 percent of the Gross Vechile Weight Rating (GVWR) can be put on either the front or rear axle, with a bit of a saftey margin.