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V4S wrong speed from sensor compared to other devices

My girlfriend has a 4s and it is connected to a Garmin speed sensor when cycling indoor. 

The sensor is also connected to my old Edge800 computer. 

There is a huge difference in the speed shown on the Edge and the V4S while an activity is started - Edge shows 18km/h and V4s shows only 12km/h

Both devices have the wheel size manually set to 2155. But the speed difference is huge, 

I've also added the sensor to my Fenix 6, set manually the same wheel size  and ran a test activity. It shows the same speed on Edge and Fenix6.

So it seems it's something with the V4S. But what could be the issue?

Did any of you had similar issue?

  • Is this the Speed V2? I'd have to simulate this outdoors, but first I need a better auto calibration of the wheel size.

  • No. It's not the V2. The V2 is installed on my bike 

    I suppose it:s V1 but i i have to recheck

  • I have made several test activities for Garmin Support. Recorded a test activity on the V4s. Fenix6Pro and Edge830. 

    It looks very strange. Especially the speed activity graph in Garmin connect - it shows a closer to reality average speed but the beginning and end of activity speed is missing. During the test activity the speed shown on the watch's speed data field never went higher than 10-11km/h, and the other devices show 18-19km/h

    v4s speed graph

    Edge830 speed graph

    Also, a video showing  way different data between V4S and Edge800(with the same wheel size of course)

    https://photos.app.goo.gl/GBgv8KKEq2kqHMyn6

  • I have to ride on mea culpa road and make your day a funny one. Please feel free to laugh but be careful not to fall from your chair.
    This might harm your body integrity irreversible. :-D
    While trying to take measurements with additional sensors I've added Tempe and Tacx speed/cadence sensors to the V4S. Seeing the temperature at ~66 when my Fenix6 was showing ~19 made me realize it's showing Fahrenheit. This led to another breakthrough realizing the speed was shown on miles instead of km(in GC mobile was shown , of course, in km)
    I would consider the topic now closed. What about you?!? Unless you want me to provide you more fun source issues. ;-)