Gear Inches

Gear Inches – what a curious term. Basically, it tells you how hard a bicycle will be to pedal: higher numbers are more difficult and lower numbers are easier. Specifically it tells you many inches the rear wheel moves when the pedals are rotated one complete turn.

The specific equation is: gear/inches = (front gear/rear gear) X rear tire diameter.

Two examples:

  1. front gear = 48T, rear gear = 11T, rear tire diameter = 25.4″, the gear/inch = 110.8
  2. front gear = 26T, rear gear = 34T, rear tire diameter = 25.4″, the gear/inch = 19.4

Why worry about gear inches, you ask? Whether looking at a new bike, changing your current setup, or comparing what friends are riding, gear inches provides an easy way to compare different bike setups.

When looking at a new bicycle, rather than saying, ‘I currently ride a 48T front gear, an 11T rear gear, and a 26″ rear rim with 1.75″ tire size. How does this bike compare?’ It could be simplified with a, ‘My current bike has an 111-19 gear/inch range. How does this bike compare?’ Then, if the gear/inches indicate that the bike will be too difficult (or easy) for you, you could discuss changes before purchasing it and discovering things are amiss.

In my case, recumbents come with many different rear rim sizes (700c, 26″, 24″, 20″) and many different tire sizes in both metric and English dimensions. I know my capabilities for pedaling a heavy load uphill, so knowing my gear/inches, particularly the lower number, helps me evaluate different bicycle brands and types.

Generally speaking, most bikes come with a higher gear/inch set up than the average cyclist needs. ¬†According to many orthopedic doctors and professional trainers most bicycle related knee injuries come from pedaling a gear/inch that is too high. Using a setup that is too high results in a slower cadence and ‘muscling’ up inclines and rough roads. It may not be as sexy, but having a lower gear/inch setup will allow the average cyclist (like me) to have a higher cadence, resulting in less chance for knee injury. Seldom do I need my highest gears but my lower gears are used quite frequently.

On the fully loaded cross country bicycle ride I used a gear/inch of 111-19; the low end was just barely low enough on the steeper grades. I am now shopping for a different bike and am looking for something on the low end of 17-18. I’ll probably have to do my own gear conversion since ‘as advertised’ touring bikes don’t come anywhere near this low.

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