07 Measurement

We talk a lot in Up Up Up about target cadences.  Start at 20 RPM, finish at 90 RPM, repeat etc.

How do you measure this?

Simplistically, you would assume that you'd use a cadence measuring device - many of the more expensive bike computers measure cadence, some with a magnet on a crank and a sensor, some with an inertial sensor.

Neither of these methods work for us.

Oh?

They work for steady state efforts, which is not what we do most of the time.  If you consider that for each pedal revolution on a typical gearing setup, you may be traveling 8-10 meters per pedal revolution. This gives us very poor resolution for our cadence measurement. If our effort is, for example, a rolling quarter lap, a typical strength effort, we are going to get only 6 or so pulses from our cadence sensor.  We'll get all sorts of noisy data from this.  It's pretty close to useless.

The shorter the effort, the less useful a cadence sensor is.

Consider instead using speed. You know from basic maths, that a speed equals a cadence.  You also know that the circumference of a typical track wheel and tyre is around 2 meters.  So now, you're getting a pulse every 2m, not every 8-10m.  That's 4-5 times more accurate.  You can improve it further by using two magnets on your wheel, and halving the circumference you tell the computer, then you get a pulse every meter.  Much better!  And you don't need to fork out for a hundred dollar fancy computer with a bunch of features you don't need and that is optimised for outdoor, steady state measurements.  Just get a cheap computer that can record maximum speed.  That time you spend sitting on your backside between efforts, you can use to work out the speed you need to hit,  on the gear you're using, to achieve your target cadence.  We have a chart you can use that helps.  The Kiwis have been seen to have a very high resolution speed sensor on their disk wheels, using an optical sensor and a black and white pattern around the hub. Most over the counter bike computers can't be calibrated to deal with such small "wheels", but you could post-process your data if you go nuts adding more magnets to your wheel, or you could break out an Ardrino and make your own.