Use a strong neodymium magnet. Stick it to the end of the pedal spindle. See this thread
. For instance: Radio Shack 3/8 inch
I opened up a dead hard drive and got the strong pair of magnets from the swing arm. I had to score and break one in two to fit into the end of my crank arm. (I had one fall out somehow, even though they stick to the steel pedal spindle very well. I used some "goop" type of glue around the edges on the replacement.)
There's a half inch gap between the cadence sensor on my chainstay, and the pedal spindle magnet. It works great, and there's no zip ties on the crank.
You can press the little button on the Garmin cadence sensor, and it'll blink each time the magnet comes by. One color is the cadence sensor, and the other is the wheel sensor. So you can see if the gap is too big to work reliably.
These magnets are very strong. I stuck one of the disk drive magnets to my fridge, and couldn't pry it off with my fingernail. I had to slide it off the edge of the door.
Last edited by rm -rf; 07-18-11 at 09:50 AM.