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Silly speed readings by Garmin speed sensor on canal towpath

GordonFK
over 6 years ago
Hi!
I'm getting some impossibly high speed readings when cycling on some parts of a canal in my hometown (the canal is Regent's Canal in London). I haven't tried all the canals around, but the readings go off as soon as I enter certain parts of the canal towpath, systematically.

See this activity: https://connect.garmin.com/modern/activity/3145511677
The sensor goes completely bonkers as I enter the canal, and comes back into its senses as soon as I leave it. Some parts of the canal it doesn't happen, but some parts it does it every time.

I've got it with the sensors on both my bikes, plus a replacement one... So three sensors, and as many devices (Garmin Edge 1000, Garmin Edge Explore and Vivoactive 3). Whatever the combination, I'm getting impossibly fast readings (between 90 and 120km/h) on some parts of the canal, systematically.

I thought it could have something to do with being near the water? Like some sort of echo or something? Not sure why some parts of the canal and not some others either...
It seems like a design flaw, is there another type of sensor that wouldn't have that problem? I'm having to disable the sensor on my commute, which is quite annoying. Also, would be nice if connect could fix speeds and distance based on GPS data!
  • 0 over 6 years ago
    Sorry, you specifically stated that you own three sensors and I said that you have two (!) connected at the same time. Now you write "I don't have two obviously". Well, to me, it is not obvious at all why you don't have two!


    Ok sorry if I'm being confusing. I don't have two sensors connected at the same time.
    If you want the full story, I own two bikes.
    Bike 1 had a sensor I got with my Garmin Edge 1000, the sensor got lost or broke at some point a few years ago so I got another one.
    Bike 2 has a sensor I bought standalone.

    So I currently own two sensors, one on each bike. In total, I used three different sensors. I have seen this faulty behaviour from all three sensors, but I'd never use two sensors at the same time.

    So, what software did you use that makes it look that the ride is with two sensors?
  • 0 over 6 years ago
    GordonFK, about the Garmin magnetless bike sensors...

    some info...

    ">Any major issues with Garmin's new magnet less speed/cadence sensors?">Any major issues with Garmin's new magnet less speed/cadence sensors?




    Yes I had read this topic. It's interesting but this issue is too reproducible across different bikes, different sensors, to (in my opinion )blame it solely on a magnetisation of the chain. Also it's location specific, so at best magnetisation would be just a factor. And this happens over several years, so with different chains, different weather conditions...

    But I understand that proper diagnosis would require me to ride my bikes over that path, with the sensor attached to the front wheel. Possibly over the next weeks I'll do it but it's a lot of work for something I'm pretty sure is not the problem.

    If someone could give me a reference for an application that allows me exploring FIT file metadata, I could compile a list of activities I have with a suspicious max speed, and group them by sensor ID, Garmin device, date, etc.. From a quick look in Connect I have 26 cycling activities with max speeds over 70km/h (out of 3753, so less than 1%). Maybe some correlation will be more obvious!
  • 0 over 6 years ago
    It is more likely something close to to towpath that is generating a strong magnetic that is causing the problem rather than anything on your bike. When you are not on the towpath your speed looks OK. There could be some cable conduit running along by the towpath that is not insulated.

  • Former Member
    0 Former Member over 5 years ago

    Haha. Got exactly the same on the same canal, between vic park and 2miles west.

    I was totally blaming a faulty sensor/battery, but checked my strava logs. And it seems to only appear there!

    No real idea of why though. Some kind of signal jammer?

  • 0 over 5 years ago in reply to Former Member

    I actually got a new Garmin sensor since then, a Speed Sensor 2 (the one that records activities), and the same thing happens. I think there's something under the tarmac on this stretch of the canal. Happy to know someone else has seen the behaviour in the same place! I don't think it can technically be fixed without seriously tweaking the tech though sadly...

  • 0 over 5 years ago in reply to GordonFK

    These speed sensors use the Earth’s magnetic field rather than using a more reliable, but likely more expensive accelerometer... I'm not an electrical engineer but the former can probably freak out under numerous circumstances. Not too far from where I ride are extremely high iron content rock that are sometimes magnetic. These rocks will throw out a compass by a long way. Also if I ride under large electric lines, the speed sensor readings can be thrown out too.

    Some riders have even claimed that the speed sensor gets thrown out by the proximity of the moving chain and cassette on the rear hub and have to revert to using the sensor on the front...