I was curious what other folks around the world were running for their fixies/singlespeeds. Low and behold I found this great survey on gear ratios and the conditions under which people use them.
Just a little math tidbit for determining gear ratios on a fixed gear bike…
If you know RPMs and want to determine speed:
- SpeedMPH = RPM * FrontTeeth / RearTeeth * WheelDiameterInches * Pi * 60minperhour / 63360inpermile
Which factors out to:
- SpeedMPH = RPM * FrontTeet / ReadTeeth * WheelDiameterInches * 0.002975
Or if you know speed and want to see how fast your legs will spin:
- RPM = SpeedMPH / (FrontTeet / ReadTeeth * WheelDiameterInches * 0.002975)
As an example, lets say I have a 48×16 fixie with 26.5 inch diameter wheels. Spinning at 100 RPMs will put me at:
- SpeedMPH = 100 * 48 / 16 * 26.5 * 0.002975 = 23.65 MPH
And if I’m cruising down a hill at 30 MPH, how fast are my legs going?
- RPM = 30 / (48 / 16 * 26.5 * 0.002975) = 126.84 RPM