Erratic speed reading - revisited 2020 Trail

[mojonaut]

A while back I had the erratic speed display error and after some research replaced the sensor and the problem went away.... sort of.

I am noticing on long rides where I use assist a lot or short rides on warm days the problem comes back almost as if it is heat related, the odd thing is if I stop pedaling and just coast along the speed immediately shows as constant. The moment I begin to pedal the speed reading jumps around again, it's almost as if engaging the motor is causing some sort electrical interference. If it were solely a magnet/sensor issue it would still be erratic when coasting.

Has anyone come across these symptoms before?

 

[Rikster]

Had the same issue, sounds likes your cables are getting pressed. I dropped the motor and checked the wires, they were pressed flat in one spot. Rerouted the cables where they have more room (2 mm shift ) while pussing the motor back in its place. No problem with the speedo no more.

The easy way is to put the bike upside-down, losen and lift the motor out of the frame (keep the cables plugged in), check for flatspots. If theres no copper wire in sight (then you need a new cable-set, or put soms tape around and hope for the best), put the motor back in its place but keep checking if the wires keep a bit of play. If they are tight, the they are stuck somewhere and you will have the same issue again.

 

[mojonaut]

Had the same issue, sounds likes your cables are getting pressed. I dropped the motor and checked the wires, they were pressed flat in one spot. Rerouted the cables where they have more room (2 mm shift ) while pussing the motor back in its place. No problem with the speedo no more.

The easy way is to put the bike upside-down, losen and lift the motor out of the frame (keep the cables plugged in), check for flatspots. If theres no copper wire in sight (then you need a new cable-set, or put soms tape around and hope for the best), put the motor back in its place but keep checking if the wires keep a bit of play. If they are tight, the they are stuck somewhere and you will have the same issue again.

Hi

Thanks for your suggestion but I'd already tried something else and wanted to give it several rides before I could be sure I had fixed it before replying.

So what I found after removing the magnet from the disc, was it was only partially filled with epoxy and the magnet was skewed, so one end of it was visible and possibly in direct contact with the disc. I cut out a spacer from a plastic milk bottle and refitted, now this moves the magnet very slightly nearer the sensor but also insulates it being in direct contact. So I'm not sure which of these two conditions has cured it, but it has, I've been out on several >50mile rides and on some of the hottest days we've had in the UK this year and it has behaved flawlessly.