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Gear Inches Explanation

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  • Rich Wood
    In America and Britain bicycle gearing figures are directly related to the old high wheeler bicycles of the 1880 time period. If you see a gear inches listed
    Message 1 of 1 , Oct 9, 2008
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      In America and Britain bicycle gearing figures are directly related to
      the old high wheeler bicycles of the 1880 time period.

      If you see a gear inches listed as 50" this is how far a 50" diameter
      high wheeler front wheel would move in one revolution of the pedals,
      which were directly attached to the front wheel spindle. The actual
      distance moved forward would be the listed gear inches X Pi. For a
      50" gear then the actual forward movement would be 50 X Pi or 157".
      For a 100" gear the figure would be 314".

      This is IMO a antiquated system as it is not at all intuitive and
      unless you are an experienced bicyclist with some familiarity with the
      concept then you cannot relate the figures to actual riding experience.

      A approximately 20" low is the common low for a 24 through 30 speed
      derailleur mountain bike or a loaded touring bike set up for touring
      in mountainous terrain.

      A 110" or so high is in the range used by a road racer, downhill racer
      or quite athletic light sports bike rider for use in good conditions.
      For specialized races such as time trials, or for someone who loves to
      pedal as fast as possible downhill, the top gear might be closer to
      125" but the rider risks knee problems if used inappropriately.

      In Europe outside England, and in most of the rest of the world,
      bicycle gearing is referred to as "Development" and is listed in
      meters. It is the amount of forward movement the bike achieves in one
      turn of the crank for the selected gear.

      An close approximation translation between the two systems is as
      follows:

      12.5 gear inches is 1 meter Development.
      20 gear inches is 1.6 meters Development.
      25 gear inches is 2 meters Development.
      50 gear inches is 4 meters Development.
      100 gear inches is 8 meters Development.

      To me this is a more logical system. I see signs that it is gradually
      being adopted here too as I have recently seen some American bicycle
      makers starting to use it.

      Rich Wood
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