I just bought a Specialized Sirrus and tried to hook up my Garmin 305 and found that I had to make a choice between cadence and speed. There was a really large difference between the pedal and the lowest bar that connects to the rear wheel. I tried using quarters and double sided tape to decrease the distance between the magnet and sensor, but that didnt help much.

Should I be looking for a different unit? I would like cadence, speed and HR, since I am biking to give me a better workout without the impact on my ankles and knees that running was giving me.

I use a Cateye Astrale with no problems.

GSC10 right? Common problem. Move it toward the rear of the left chain stain where it gets closer to the crank arm.

Tip: For a clean installation, you can stick a rare earth magnet to the inside end of your pedal spindle for cadence. I use 3x12mm magnets for this purpose. Alternatively glue the magnet to the inside of the crank arm with RTV.

Better yet, got the Garmin user forums and search and post your questions there:

https://forums.garmin.com/forumdisplay.php?f=20

Have you tried contacting Garmin? Anyway, this is a problem specific to one bike, not Spec's bikes in general - hybrids tend to be have longer chainstays than road racing bikes and Garmin seem to have assumed that the computer would be mounted on a road racing bike. If possible I'd take the computer back and get a refund.

I had the same problem with one of my bikes. Solved it for under $2 by sticking two rare earth magnets on my pedal.

https://www.harborfreight.com/10-piec...ets-67488.html