Gear Inches / Gain Ratio
(chain ring/sprocket x wheel diameter) / (wheel radius/crank length x chain ring/sprocket)
Using default inputs: 26 inch diameter wheel • 6.875 inch crank arm length (radius ratio = 1.89)
  30 26 23 20 17 15 12
24 20.80 / 1.51 24.00 / 1.75 27.13 / 1.97 31.20 / 2.27 36.71 / 2.67 41.60 / 3.03 52.00 / 3.78
38 32.93 / 2.40 38.00 / 2.76 42.96 / 3.12 49.40 / 3.59 58.12 / 4.23 65.87 / 4.79 82.33 / 5.99
48 41.60 / 3.03 48.00 / 3.49 54.26 / 3.95 62.40 / 4.54 73.41 / 5.34 83.20 / 6.05 104.00 / 7.56
Printable Chart


These are values for my bike (Bridgestone MB-1)
Enter the values for your bike and press Calculate
Crank arm length in inches  needed for gain ratio, only
Wheel Diameter in inches
Chain Rings (number of teeth)
Rear Sprockets (number of teeth)
Separate chainring and sprocket values with a comma (values may be ascending or descending).

chainstay length (in.)

enter to calculate proper
chain length = 54 inches


Use default inputs

Gain Ratio = for every inch of pedal travel, the bicycle will travel Gain Ratio inches.
(Gain ratio concept and formula courtesy of Sheldon Brown - http://www.sheldonbrown.com/gain.html.)

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