Formula for figuring RPM
 

After reading and seeing all the questions on which gear to run, I thought maybe someone could use the formula to figure gear ratio to engine RPM.

Gear ratio X 336 X MPH divided by tire diameter = RPM in 4th gear
Multiply that answer by .68 (overdrive gear in tranny) = Engine RPM in overdrive

4.10 X 336 X 70 = 96432 divided by 25.5 = 3781 rpm in 4th

3781 X .68 = 2571 rpm in overdrive