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Old 05-03-09, 04:30 PM
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I don't see that adding a small magnet is likely to do anything to help trip the typical inductive loop detectors used to trigger traffic lights.

They operate on the same principle as the metal detectors seen in use by people at beaches who are looking for coins and jewelry buried in the sand. Your bike already has a considerable amount of metal in the rims (closest to the detector) and other parts so a little magnet isn't going to add much. The detectors are generally adjustable in sensitivity and can be turned up to detect bicycles. But there's a rather delicate balance since they shouldn't be too sensitive or they'll trigger based on vehicles in other lanes. I've found the local traffic departments to be pretty good about coming out and readjusting the sensitivity if they're made aware of a problem sensor that's not picking up bicycles.

I find that I'm able to trip most sensors by positioning my Cannondale over either an edge of the loop (for single loop types) or in the center of the loop (for figure-8 or multiple loop types). Laying the bike down over the sensor makes it even more likely to be successful by getting the metal parts of the bike as close as possible to the sensor. Note that any type of metal will work - there's no need for it to ferromagnetic.
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