RPM vs. MPH:
These calculations are useful in selecting rear tire diameters and rear gear ratios.
MPH =
Tire Diameter in inches * RPM
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336 * Diff Gear ratio * Trans Gear Ratio
RPM =
336 * Diff Gear ratio * Trans Gear Ratio * MPH
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Tire Diameter in inches
Rearend Ratio =
Tire Diameter in inches * RPM
-----------------------
336 * MPH * Trans Gear Ratio
Tire diameter in inches =
336 * Diff Gear ratio * Trans Gear Ratio * MPH
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RPM
I found this formula here.
Mustang Math