I did that same calculation (using higher math!!.....actually junior high-school math!) My 9.00-20 tires measure out to about 40"(3.33') diameter.

I calculated that I would need to have a rear-wheel rpm of 504 rpm to get 60 mph. (with a 0.7 OD)

Simply calculate the rolling circumference[C=Pi x Dia] of the tires.

C = 3.14 x 3.33'........10.47 ft.......1 mile is 5280 ft.....60 mph is 5280 ft/min.......

Then divide the rear tire circumference into 5280! 5280/10.47 = 504 (rpm)

504 is rear wheel rpm needed to go 60!

Now multiply 504 times the rear axle ratio to get drive shaft RPM to go 60.

504 x 5.83 = 2938 rpm and using the 0.7 OD....2056rpm!

All you need to know to make this work is the rolling diameter of the (rear) tires, Which you can measure and the rear axle ratio (and OD ratio if installed)




Cheers,


Rick