I have a $15 Bell (Spinfit) Speedometer that I bought from the general Sports store. I was thinking.... all I need to do is glue the magnet to one of my crank arms, position the sensor accordingly, and all of the sudden, I have a cadence meter. I think the wire is long enough, but I *may* have to pony up the extra $10 for the wireless.

But, you say, the speedometer was designed for readings in MPH or KPH. I reply, set the tire diameter to 1667 (for KPH readings) or 2688 (for MPH readings), and the Math should all work out - and your speedometer will *say* it will be reading MPH/KPH (and really high numbers, too!) but it will actually be cadence in RPM.

As you can probably tell, I haven't gone through with this yet... but I'm going to buy another speedometer sometime this weekend and try it out. If anyone else buys one, make sure you get one that can read up to 200 MPH/KPH. The Bell SpinFit can, but not every one can.