La vie de vélo

Adventures in cycling and life

What gear is everyone else using? A neat survey..

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.

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September 23, 2008 Posted by | Fixie, Math | 1 Comment

Calculating Fixed Gear Speeds and RPMs

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

September 21, 2008 Posted by | Fixie, Math | 1 Comment