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Garmin 1040 inaccurate speed reading

carbonsteve
3 months ago

I have had three Garmin 1040 and had to send all three back as they all had the same problem an inaccurate speed reading whilst riding, when i was going along a tree lined or even low bush roads the speed would jump from 20mph down to 10-12mph and bounce about until i got to a clearing, i have to stress this wasn't densely overhanging trees but low to mid brush, and only when on a clearing did it read at a constant, this happened on every ride and i still have my Garmin 1030s and used both at the same time and the 1030s never had a drop of speed infact never had a problem with it at all so i am able to compare the bad 1040, i have now had to buy a Karoo 3 which is perfect as i couldnt ride with a unit as bad as this

  • 0 3 months ago in reply to pdj-84

    To me it looks little bit as if the data from the cadence sensor might be perhaps confused for speed sensor. That was my suspicion already at the fist example, but if you tell it happens also with no speed sensor, then it looks even more likely. I do not know whether it is due to some hardware interference, because of a wrong setup, or due to a bug in the 1040 firmware, or a problem with the sensor(s), but I'd recommend to do a longer test ride with no sensors at all, just to see whether the problem occurs again or not.

  • 0 3 months ago in reply to trux

    This made me think that might be what is happening with me also.  The gravel bike (Merida) that this happened to with me last week has no speed sensor but has a magene cadence sensor (on the pedal) which can also function as a speed sensor.  I just checked it and its definitely acting as a cadence sensor but that doesn't mean its not randomly swapping between identifying as speed and cadence (I have had trouble with faulty versions of these sensors previously).  Riding two days ago on a MTB (Cube) with lots of trees about & no speed or cadence sensor the 1040 seemed to show consistent speed.  Riding yesterday on a clear road (no trees) on a road bike (Trek) with a garmin cadence sensor and no speed sensor the 1040 showed consistent speed all the way.

    I'll take the magene cadence sensor off the gravel bike next time I go out and see if it makes a difference to this problem.

    Here are the activities for each of those rides.  The speed trace for the Trek (Road) and Cube (MTB) are much smoother than the Merida (Gravel) .  Towards the end of the ride on the Merida you can see the speed regularly swapping between a very low speed and a somewhat higher speed - I was riding at a fairly constant speed then.

    Merida: https://connect.garmin.com/modern/activity/18404948249

    Trek: https://connect.garmin.com/modern/activity/18450530309

    Cube: https://connect.garmin.com/modern/activity/18441846718

  • 0 3 months ago in reply to GregF888
    GregF888 said:
    I just checked it and its definitely acting as a cadence sensor but that doesn't mean its not randomly swapping between identifying as speed and cadence (I have had trouble with faulty versions of these sensors previously)

    The data from the cadence sensor has a lot of gaps in it. And since it happens also during hill climbs, it does not look like the gaps are there because you stopped pedaling. So yes, it supports the theory that the sensor may be perhaps switching from Cadence to the Speed mode. Though, I do not know whether it is really the sensor, or rather the processing on Edge that causes the wrong data interpretation.

    See below a zoomed section from your Merida ride - the orange curve is the Cadence (elevation green, and speed gray). Far too many gaps in the cadence data, so there is definitely something wrong with the sensor (or its processing).

  • 0 3 months ago in reply to trux

    Thanks for the feedback .  The 1040 keeps searching for sensors all the time & the 1030 I had previously stops searching for sensors soon after turn on.  This is why I probably never noticed this bizarre speed display on the 1030 - it just used the gps all the time but the 1040 may be swapping between GPS and sensor when the GPS gets weak (with trees about).  I have removed that cadence sensor from the Merida, lets see if the speed is more consistent next ride.

  • 0 3 months ago in reply to trux

    I was riding my Trek (road bike) yesterday without a speed sensor & after stopping mid ride for a coffee I noticed the speed reading very low again.  I also noticed cadence was showing zero.  This bike has a Garmin cadence sensor but it was showing as a speed/cadence sensor in settings. I disabled the sensor in sensor settings and then the speed reading returned to normal for the rest of the ride. I checked the cadence sensor battery when I got home and it was about 2.8v.  So I think this confirms that when a cadence sensor battery gets flat my 1040 starts interpreting it as a speed sensor when I don't have a speed sensor on the bike.

  • 0 3 months ago
    I recently purchased a Garmin Edge 1040 Solar which was delivered Friday 7th March.
    I've used the item twice and experiencing speed fluctuation/jumping (+/- 1-3mph).
    I've tried various GPS settings and a factory reset to no avail.
    The problem does not occur when using a wheel sensor.
    With such an expensive model, this solution is merely hiding the fault. 
    My existing Garmin Edge 810 & Etrex 32x do not suffer from this.
  • 0 3 months ago

    i have the same problem with my garmin edge 1040 : when riding, from time to time, on the speed screen I have a red square and my actual speed drops from say 30 km/h to 4 or 5 km an hour. I had it yesterday about 5 or 6 time (if not more) during a 5 h ride, speed drops for roughly 20 seconds to under 10km/h . Any help to fix this would be welcome. GPS is on Multi-Band GNSS and I am using garmin rally x ( single) power pedal. <firmware is updated.

  • 0 3 months ago in reply to zeironchicken

    Have a read of my various comments on this low speed display appearing on my 1040 when the cadence sensor battery went flat (2 different bikes, 2 different sensors). I have put a new battery in the garmin cadence sensor on my road bike and tossed the magene speed/cadence sensor on my gravel bike & the speed is rock solid on both bikes now.  Its a definite bug in the 1040 IMO but at least I found what causes it for me.  Hope this helps.

  • 0 3 months ago

    Speed sensor will fix this. GPS is a relatively weak signal and it was designed so that you had to have a clear signal of the sky. A Car GPS can be more reliable because guess what, they have a speed sensor as well.