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Simple maths

by Carl Brewer last modified 2010-09-26 00:44

How many revs?

Some simple maths today.

A 500m ITT, on a 6.5m rollout (J17 gearing) is 77 revolutions, or about 39 pedal presses per leg.  On a 6m rollout (J15), it's 83 revs, 42 per leg.   Not much difference!

If the 500m is ridden in, for example, 39.8 seconds on a J15 gear, the average time per revolution is 0.48s, or 0.24s per each leg stroke. The average cadence is ~118rpm.  These averages are nonsense, the rider accelerates from a standing start which totally blows the average cadence calculation.

So, how about the flying 200, where the rider will mostly maintain speed for the distance (with some losses in the last 50m or so).  Let's take our J15 rider, and a sample time of 13.455 seconds.  200 metres at a 6m rollout is 33.3 revolutions, or about 17 pedal strokes per leg.  In 13.455 seconds that's 0.4s per rev, or 0.2s per pedal stroke.  If you consider that the leg only produces useful power in a short range of the pedal stroke, let's say about a 60 degree arc, that's two thirds of the pedal stroke that contributes useful power, so our J15 has about 0.13s to push as hard as they can per leg, 34 times (not including the windup, of course).  It's even less time if the rider's going faster, of course.  The Australian JW15 record for the F200 is 13.310s (Imogen Jelbart) and for JM15 it's 11.968s (Mitch Docker), Immy was spinning at around 150rpm, Mitch at close to 166rpm.  At those cadences each leg has around 0.1s to produce power and about 0.15s to recover before doing it again.  That's less than the blink of an eye.

I wonder how close the girls can go to the boys as juniors? If the female talent pool was larger would we see JW's keeping up with JM's, at least in the J15 and J17 groups? At these cadences on little gears it's not a strength game, it's how fast you can fire your triple extension and recover to repeat it.

Got to get 'em spinning when they're young ...  The game changes in J19 and above, but we've already discussed that here!

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