Cadence
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Speed From Cadence |
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You want a rough idea of how fast you were going. You know you were doing about a 90 cadence in a 53 x 13. So how fast was it? Use the input form on the right to enter cadence, number of teeth on the front chainring, and number of teeth on the rear cog. Then click on the Run Model button. The input form returns a table with your data and an estimated speed along with a plot of speed verses cadence. So how do you estimate cadence? One way is to count the number of revolutions of the pedals in six seconds and multiply by 10. Another is to count revolutions in 15 seconds and multiply by 4. Most of the error of these methods comes from missing partial revolutions at the start or end of the counting period. So the longer the period, the better the estimate. Both methods require a watch or other timing device. After some experience, one can make a good guess at cadence. And the guess if often good enough to estimate speed. Wheel diameter varies slightly by tire and inflation pressure. You can estimate diameter by measuring the distance covered by rolling the rear wheel one revolution and then dividing by Pi (3.14159). The result is the diameter of the wheel. Or you can use the default value and keep things simple. Here is a typical situation. You are going fast down a hill and spin out your top gear, a 53 x 11. You know you can spin at least a 110 cadence. What was your estimated speed? The model gives 41.8 mph. |
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