# Singlespeed & Fixed Gear - formula/program for converting speed to RPM and vice versa?

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wearyourtruth
11-19-09, 12:22 PM
is there a formula or program that allows me to convert my mph to rpm based on my gear ratio? or vice versa. just curious really but i haven't found anything online.

11-19-09, 12:39 PM
diameter(mm)*pi*rpm*60/1609344

ismellfish2
11-19-09, 12:44 PM

JiveTurkey
11-19-09, 01:00 PM
http://sheldonbrown.com/gears/

Set to "MPH @ 100 RPM" (or "KPH @ 100 RPM"). Once you know your speed at 100 RPM, it' pretty easy to calculate your RPMs at other speeds.

E.g.: If 15 MPH = 100 RPM, then new RPM = [X/15 * 100], where "X" is the new speed.
If your new speed equals 16 (meaning, "X"), then your new RPM = [16/15 * 100] = 106.7 RPM.

paktinat
11-20-09, 02:02 PM

teedoff087
11-20-09, 02:11 PM
Yeah ^^^ What he said. Rabbit does exactly what you want. You can also download the applet so you don't have to go to that webpage every time you want to calculate.