Tuesday, April 19, 2011

Returning to Bicycle Gearing

I came across my original table for calculating the gear ratios and gear inches of my original road bike. Searching through my older posts, I realized I never put that information out there, even after I had decided to buy the Bike Friday New World Tourist.  Determined to not dive into spending more money without guaranteed results, I had used this very fine site to determine the inches and ratios of each bike to make sure I would be gaining something meaningful.

  1. make a table with the number of teeth on each chain ring in the front and each cog in the back
  2. divide the front chain ring teeth by each of the rear ring cogs to get the proportional (ratio) size difference between them for each combination
  3. mulitply the size of your wheel by the proportion (ratio to 1) to get the gear inches.
Note in the case of my two bikes that I lost a little at the top end of the BF (I can't pedal downhill as fast), but gained significantly at the bottom end. The highest gear inch on the BCA is over 100 and on the BF it is only 94.55.  The lowest on the BCA however, is 28.93.  On the BF, I can get all the way down to 18.75.  Screaming downhill was far less important than effectively chugging up those steep hills. My top speed on the BF was 49mph, by the way.

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