Garmin randomly misreporting speed? 28.34

During a steady group ride, open road (no tall buildings, water on one side), I was seeing random drops in reported speed, from ~37kmph suddenly reporting 17-20kmph.

I have the speed sensor on front wheel.

It's visible in the activity record, noting numerous speed drops whilst cadence is steady. I was in a group of ~20 riders doing rolling turns.

Each speed drop is bad data.

0 Luko79 3 days ago

is it bumpy road? and if there are electrical cables under the tarmac, that can fool this accelerometer-based speed sensor always (these things are happening at same place)

0 Hqduong 3 days ago

I had this issue, it ended up being my speed sensor being mounted on the rear wheel. IT was always about half the speed. Turns out being on the rear wheel interferes with how the sensor detects rotation.

0 L.Rouge 2 days ago in reply to Hqduong

Hqduong said:
it ended up being my speed sensor being mounted on the rear wheel

Never been a problem for me?? (8 - 10 years, including 3+ with 1040).

0 Cristox 2 days ago

Looks like an almost empty battery

0 felixrising 2 days ago in reply to Luko79

Hi, no the road is very smooth and flat in that section.

0 felixrising 2 days ago in reply to Cristox

Both the 1040 battery and speed sensor are in good condition and battery level.

0 felixrising 2 days ago in reply to Hqduong

I also used to have it on rear wheel for over a decade. It's currently mounted on the front wheel.

0 DuaneHebert 2 days ago in reply to felixrising

Are you using a battery with the child proof coating? I've had similar with that. Wiping down with alcohol solves the problem. Also could be a bad sensor.

0 Luko79 1 day ago in reply to felixrising

i see it is Brisbane, but i dont find you(r activity) on Strava on this segment (i checked both directions ). Can you send me the original FIT file in private message?

0 felixrising 18 hours ago in reply to Luko79

@luko79 I don't seem to be able to DM you. This is the activity: https://connect.garmin.com/modern/activity/20796985242

@duaneherbert 1040 is wearing a silicon protective cover that doesn't extend to the screen - has been since day 1. But otherwise no protective coatings etc.