Friday, September 14, 2012

Proper gearing

I did a bit of research to find out more about proper shifting technique for long distance biking. It turns out that it is more efficient to rotate your feet at a higher rpm with lower gearing. The ideal rpm is roughly 80-85, which is much faster than most people would be pedaling.

I also counted my gearing on the front and back gears to see what that might translate into for mph.

On the front gear I have 3 gears, with 30, 42, and 52 teeth respectively.
On the rear gear I have 8 gears, with 12, 13, 15, 17, 19, 21, 23, and 25 teeth respectively.

Given the tire sizing, one complete tire rotation is roughly 86.35 inches traveled.

Putting this all together I can figure out the ideal mph for each gearing ratio, as follows:

52 teeth 42 teeth 30 teeth
12 teeth 28.34 22.89 16.35
13 teeth 16.16 21.26 15
15 teeth 22.7 18.31 13.08
17 teeth 20.01 16.16 11.51
19 teeth 17.9 14.45 10.33
21 teeth 16.22 13.08 9.35
23 teeth 14.78 11.97 8.5
25 teeth 13.6 10.99 7.85

This has a few interesting features. First, I should be pedaling a lot faster, instead of harder. Second, I had always assumed that the middle front gear was always a higher ratio than the smaller gear. It turns out that some of the ratios with the smaller gear in the front can actually be higher, so it is not always a low, medium, high gearing in terms of speed.

I can use this information with my bike computer to determine which gearing I should be using, in an ideal situation. I have previously just been going based on changing gears whenever it felt too easy or hard to pedal. I'll have to see how this actually goes though, but now I have some data to use.

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