When I took the front wheel off of my road bike to mount it on the rollers, I found that i need to do something with the magnet and odometer from the front wheel. I tried last year to put the odometer magnet on the back wheel and that proved to be a debacle at best. I had the computer set over 2000 mm for wheel circumference. I decided to do something different this year. I used zip ties to strap the magnet to the front roller! Hahaha! I had to set the computer to 359 mm...lol.
The little white thing in front of the roller is an old fish food container with the odometer transmitter strapped to it. At least its a better set up than last year. :)