Join Date: Feb 2004
Location: St Peters, Missouri
Bikes: Rans Rockst (Retro rocket) Rans Enduro Sport (Retro racket) Catrike 559, Merin Bear Valley (beater bike).
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The only thing that the sensor does is to count wheel revolutions. The hub turns exactly the same number of times as the rim so height doesn't make any difference.
The biggest single problem with computers is getting the pick up the right distance from the magnet. Since the spokes angle inward from the hub flange to the rim, mounting close to the hub might put the magnet too close to the fork and mounting near the rim might move the magnet too far away.
I guess that technically you'll get less polar enertia by mounting the magnet close to the hub, but that force won't be enough that you'll ever feel it. If you have a large frame size, you might not have enough wire to do a neat installation if you try to mount the pickup too low on the fork.
I always try to mount the pickup in front of the fork. That way, if you ever bend something so that the magnet hits the pickup, the wheel rotation will just knock the pickup out of the way rather than jam it into the spokes.