Originally Posted by
Polaris OBark
Does this mean that it is the aluminum in my rims that is causing the induction that is detected? I had always assumed it had to be ferromagnetic, but I guess this means that assumption must be incorrect.
It's the electric currents around any closed path on your bike that trigger the sensor. Doesn't need to be ferromagnetic; only needs to conduct electricity. Any decent-sized closed loop of metal (such as the rims and/or the frame triangles themselves) ought to trigger it. Ferromagnetic metal might amplify the fields a LITTLE, but not by much -- not like an iron core to an electromagnet would -- since most of the space inside your loop is gonna be air rather than metal.
Lying the bike sideways, as some have mentioned, can work if it's a dipole sensor (so that the seam cut in the pavement looks like a single rectangle or oval). If it's a quadrupole (so that the seam looks like a figure 8 of some sort), then leaving the bike upright, right over the middle seam of the figure-8, is best. In general, the quadrupole loops, if they're set up correctly, are better at picking up bikes. This is because their sensitivity declines more rapidly with distance. Which seems at first like a bad thing, but actually means they can crank up the sensitivity to nearby objects, without accidentally triggering on a car in the next lane over.