Chris Bender, Lab Rat
- Feb 22, 2013
- Reaction score
- Garland, TX
As I understand it, it is essentially a strange gauge coupled with a cadence sensor. It is essentially measuring the power that the rider is putting into the pedals. The strain gauge part of this variety replaces the standard spider of the crank set, which is the part that ties the cranks to the chain rings. Reports out as Wattage and Cadence via bluetooth/Ant+ which my head unit receives and displays as either live, 3 sec average or 10 sec average. Quick testing on the trainer looks like 3 sec average will probably be the way to go. Supposedly accurate to +/- 2%.How does that work?
- Power can be computed as torque times angular speed, which requires measuring the torque. (Speed is easy.)
- Or it can be computed as the time derivative of ½mv², which requires knowing the mass. (Again, speed is easy, for known wheel diameter.)
There are also versions where the power is measured on the pedal itself, and at the crank arm. All have their advantages and disadvantages. Since I knew I could do the swap myself, the spider version made the best cost-performance sense for me.