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Incorrect indicated speed on Edge 1000 & Fenix 5X when coupled to a Garmin Ant+ Wheel on Speed Sensor.

phenri
over 4 years ago

Devices/Sensor Description:
The Garmin ANT+ Speed Sensor is at least 5 yo, it came originally with the Edge 1000 bundle, and has always worked perfectly. It's the type you hook to the center of the wheel with a rubber band. I just put a new battery in the Speed Sensor for the 2020 summer cycling season. I recently acquired a Fenix 5X sport watch and I got the same behavior when the Speed Sensor is coupled to the Edge 1000 and the Fenix 5X. 

Problem Observed:
When I am heading South/South-West, the Sensor Speed is accurate compared to the GPS Speed.
When I am heading North/North-East, the Sensor Speed is about 2x the GPS Speed.

This behavior is consistent with all test setups:
1) Edge 1000  Sensor Speed - Fenix 5X GPS Speed,
2) Edge 1000  GPS Speed     - Fenix 5X Sensor Speed,
3) Edge 1000  Sensor Speed - Fenix 5X Sensor Speed,
4) Speed Sensor hooked to the front or rear wheel,
5) Wheel dimensions set manually or set to auto.

How can the Heading affect the Speed Sensor output? I though the Speed Sensor was just counting the number of revolutions per sec and the Devices were converting in speed based on wheel dimension.

Is it possible there is the same software bug in both the Edge 1000 & Fenix 5X that miscalculates the speed based on the Heading?

Is the Speed Sensor broken and need to be changed? I don't want to spend another 75$ just to find out there is no problem with the Speed Sensor.

Something doesn't ad up here. Very weird bug.

For now I have to deactivate the Speed Sensor and ride on GPS Speed only.

Suggestion anyone?

  • 0 over 4 years ago

    The sensor is only sending a revolution count. Check that all units are set-up the same. Set the wheel size manually to the same value and see if that fixes it.

  • 0 over 4 years ago in reply to aweatherall

    As I said in my description above, I've already tried that. Manual and automatic wheel size on both device. Anyway, if this was the problem, the speed would not be wrong when heading North and good when heading South!

  • 0 over 4 years ago in reply to phenri

    The speed sensor is using a magnetometer to detect the rotation of the sensor in the earth's magnetic field so a strong electrical field or magnetic field could impact it. 

    I would not expect your heading to affect it, but other factors like a nearby power line could. Does this occur on the same location on your rides or is it purely direction related no matter where you are riding?. 

  • 0 over 4 years ago in reply to aweatherall

    I tried on another bicycle with different wheels and the problem is gone???

    So on my 2015 Tarmac S-WORKS with Zipp 404 carbon wheels, the speed sensor works correctly in all heading directions.

    On my old 2006 Devinci Caribou II, an old Alluminim touring bicycle, with old heavy/rugged aluminium wheels, and huge/powerfull/strong Disk breaks, the sensor speed when heading North is 2x the real speed!

    Must be related to earth magnetic filed as you say.

  • 0 over 4 years ago in reply to phenri

    Frustrating that you have an issue, but good that you have found the cause.

    It looks like you will need to use a different brand of speed sensor on that bike. One that uses accelerators. 

  • 0 over 4 years ago in reply to aweatherall

    Yep. Or I'll just rely on the GPS Speed since I only use that old bike during spring time until the roads gets cleaner. Thanks.

    Patrice