I'm using a Cateye wireless, the cheaper unit which doesn't do average speed. It works nicely, records mileage per trip and total, which is what I wanted it for. It's nice to see my instantaneous speed too. However the max speed reading ends up with ridiculously high numbers almost every ride. I don't normally check max speed while I'm riding, but the last few miles of my typical ride include a good downhill with some serious bumps. When I check it after that section it is often ridiculous.

I figure the high speed readings could be the result of the magnetic switch bouncing, especially while the magnet itself is going by. This could result in multiple readings from the detector that really don't correspond to complete rotations of the wheel.

On the other hand, maybe I really did hit 87mph on that downhill today. But I doubt I ever hit 203mph.

Has anyone else ever seen this kind of behavior?