How to Calculate Cycle Gearing

How to Calculate Cycle Gearing
Much like the common lever, the gear system on a typical multigear bike is a means of modifying the rate at which work gets done. One method of determining the rate of change from gear to gear--called the gear ratio--is to compare the relative sizes of the chain-ring gears on the crankset at the front of the bike and those of the freewheel, or cassette, sprockets at the rear of the bike. This is done by counting the number of teeth on the sprockets. The most meaningful measurement to the cyclist is knowing the gear-inch of the various combinations. This is simply the calculated ratio of the two sprockets multiplied by the diameter of the bike's wheel.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:
  • Access to the gear cassette on the rear of the bike
  • Notepad
  • Calculator
Step 1
Count the number of teeth on each gear in the chain ring and write the numbers down. There may one, two or three gears comprising the crankset.
Step 2
Count the number of teeth on each gear in the cassette and write the numbers down. There may five or up to 10 sprockets comprising the cassette.
Step 3
Divide the number of teeth on the largest chain-ring sprocket by the number of teeth on the smallest cassette sprocket. This may be an equation like 52 divided by 13. The answer, 4, is the ratio or 4-to-1.
Step 4
Repeat this calculation for each combination of gear on the chain ring and the cassette. There may be as few as 10 or as many as 27, depending on the configuration of the drive system.
Step 5
Multiply each of the ratios in the previous step by the diameter of the wheel on the bike--usually 26-inch, 27-inch or, for 700c wheels, about 26.6-inch. These products will be the actual gear inches for each combination.

Tips & Warnings

 
The smaller the gear-inch, the easier it is to pedal the bike, albeit more slowly. Generally, smaller gear-inch combinations are used for hill climbing while larger ones are used for straight terrain or downhill. Remember that the gears on the bike are used less for determining speed than they are for maintaining the optimum cadence. Speed will be determined by the rider's strength and the grade of the terrain.

Resources

Article Written By Garrison Pence

Garrison Pence has been a midwest-based (ghost)writer for three decades, taught university-level literature, and has written articles and white papers in trade publications of the Material Handling Institute, Engineering Today, Pharmaceutical, Food and Beverage Science, and Semiconductor. Pence holds a Bachelor of Arts in English and a Master of Arts in Literature.

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