Originally Posted by
carleton
For SRM Power Cranks, Cadence is calculated in the crank spider and the Cadence data is transmitted when the Power data is transmitted.
From the SRM website:
The SRM Science Track PowerMeter arms can be exchanged to fit either format.
Weight: 738 g
BCD: 144 mm
Q-Factor: 141 mm
Wireless: ANT+ Compatible
Battery Life: 1900 hours
Accuracy: < 0.5% error
Includes:
PowerMeter Spider 144 BCD
Drive and Non-Drive Side SRM Octalink Compatible Crank Arms (7075 Aluminum)
Cadence Magnet Kit
So what this magnet stands for? I wouldn't say it's for attaching to the rear wheel as it's not in the line for the spider but I may be wrong.