Can I put the speedometer sensor for my cycle computer on my rear brake line? Pretty simple question I hope. I picked up a Bontrager Trip 3 because I saw it recommended several times for rear mounting (this is on a bike that will sit on a trainer). However, I am finding that there is nowhere on the rear portion of the body that puts the speedometer sensor close enough to the spokes of my wheel for it to sense the magnet as it travels. The only place I've found that might work is on the plastic sheath around the brake line near the rear disk brake. It looks like it requires about 1-3mm distance to be able to pick up the magnet - there's almost nowhere on my bike's body that comes that close to the spokes. The brake line sheath isn't very stable (it's just hard plastic) but it seems to work.

The only other option would be about 1" of shimming near where I have the cadence sensor.

The seatstays and chainstays for the bike are extremely wide because of disk brakes.
I have had a similar problem and solved it by using a small piece of foam pipe insulation. I see no reason why a piece of sponge or similar material wouldn't work. I used two zip ties to hold the spacer in place, then positioned the sensor pick-up.