All you need to know is your gear ratio, your wheel circumference in feet, and the number of minutes in an hour and the number of feet in a mile.

RPM = (MPH X 5280)/(Gear Ratio X wheel circumference in feet X 60)

For example:

50 x 12 = Gear ratio = 4.17

Wheel circumference in feet = ~6.89 for a 770c x 25 wheel

MPH = 29

(5280 X 29)/(4.17 X 6.89 X 60) = 153120 / (4.17 X 6.89 X 60) = 88 rpm

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Last edited by bmcer; 12-27-20 at 04:08 PM.
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