Originally Posted by cyccommute

The “magnet on the bike” is an old trick that really doesn’t work. Magnets have a magnetic field but the field strength rapidly decreases with distance. Even a large magnet…larger than you want to carry on a bike…doesn’t have a magnetic field that extends very far from the magnet. Even mounted on the bottom bracket it would be too far from the induction coil to make much difference. The wheels rolled over the most sensitive part of the coil is just barely close enough to cause a change in the coil current.