Originally Posted by Wil Davis
Er, um - I'm not quite sure I understand what you're saying here - I would have thought that the only thing which changes the distance calculated by the cycle computer is the circumference of the wheel. The postition of the magnet has nothing to do with the circumference of the wheel, or with the number of revolutions the wheel makes in a mile. The speed at which the magnet passes the sensing probe will change with the distance the magnet is set on the radius of the wheel, and this might alter the signal which the sensor detects, but the number of revolutions per mile will not change…
- Wil
I see what your saying. The only cycle computer I ever had with a speedo feature had a setting for wheel size and then the instructions said to place the magnetic a specified distance from the axle. But what your saying (and I understand too) that all parts of the wheel are moving at the same RPM so regardless of where the pickup was, the timing between pulses would be the same (at a given wheel speed).
The only possible explanation of specific magnet placement would be (as you said) if the sensor measured the pulse width to determine speed (instead of counting the number of pulses over a period of time). Then the magnet placement would be more critical because the magnetic travels at different speeds depending on where it's mounted.
d.tipton