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.