The Rotor Power meter uses four strain gauges inside each crank to measure power, with a battery and ANT+ transmitter housed at the axle end. That means true measurement of left/right balance is possible and temperature compensation shouldn’t be a big issue (it wasn’t).
Rotor’s high data sampling rate of 500Hz opens up a few new options to evaluate your pedal stroke via Rotor’s software. Real time torque effectiveness (a measure of how regular your stroke is all the way round) and pedal smoothness (how much of your max power you are using to generate the power) are both possible, although it remains to be seen how you can use these to actually produce more power.
This is all well and good, but we found that the Rotor power meter read consistently 20-25 watts higher than our control meter and another meter we tested against. The data from the two meters tracked quite well, which led us to think that it was perhaps down to factory calibration being off. Of all the power meters we tested, Rotor was the only ‘outlier’ – producing values outside those of the rest – on the high side.
You really want your power meter to be accurate (close to the true value) and consistent or you can’t ever compare your data to anything else. The Rotor seems to have the consistency, which is a good thing, but it doesn’t have the accuracy.
On the positive side, we experienced no durability issues during our testing, and weight wise it’s good; our 175mm crankset, round Q-rings and bottom bracket weighing 732g. It’s also easily serviceable, although the batteries are CR2477B, which aren’t as readily available as CR2032. Pairing to a head unit and zero offset are very simple too; you just need to perform the zero once for each crank. If the calibration problems can be ironed out, this will be a good quality meter.