Just how accurate are GPS tracking devices?

Discussion in 'CycleChat Cafe' started by PaulB, 19 Jun 2017.

  1. PaulB

    PaulB Guru

    I ask because I get very different readings between trackers for the same activity.

    As an example, my Saturday ride, according to my Garmin Edge 705 shows that the ride was 51.21 miles in 3 hours 20 mins with 3,403 foot of climb. I was wearing my Garmin forerunner 235 watch and that showed the ride was 51.41 miles taking ten minutes longer with a massive difference in the climb - 2,155 foot versus 3,403 on the Edge 705!




    For the same ride!
  2. PhilDawson8270

    PhilDawson8270 Veteran

    Do either of them have have a barometer?
    cyberknight likes this.
  3. GrumpyGregry

    GrumpyGregry non-contributing ex-member

    The edge has a barometer, I don't think that model of Forerunner does and the Garmin website and t's & c's are full of accuracy disclaimers.
  4. ScottishGeek

    ScottishGeek Veteran

    Autostop 'on' on the 705 and 'off' on the 235?

    Segal's law also applies:-

    "A man with a watch knows what time it is. A man with two watches is never sure."

    Last edited: 19 Jun 2017
    classic33, Leaway2, S-Express and 3 others like this.
  5. ufkacbln

    ufkacbln Guest

    There will always be inaccuracies, enter an area of poor reception, or have a better GPSmodule in one unit and this will be evident.

    The trick is really to use these units as a comparison

    Do the same ride twice, and if the speed is faster, then you will have been faster, if your heart rate is higher than it will have been higher

    Simply because all the inaccuracies and errors are consistent for that unit
  6. DaveReading

    DaveReading Veteran

    Strange, I'd have expected the Forerunner to register a greater climb reading as it will record every time you raise your arm to acknowledge another cyclist.
    Eddy, ScottishGeek, Joffey and 3 others like this.
  7. welsh dragon

    welsh dragon a permanent vacancy now exists

    I don't think any of them are accurate. Endomondo says one thing and the LCD unit on my bike say totally different things. I trust the info on my bike more as it doesnt rely on GPS at all. The mileage counter is wired to my front wheel. I know that on my travels my Endomondo signal has dropped out numerous times. I no longer take any notice of what it says anymore.
  8. Accuracy depends on many, many factors. Dedicated GPS devices are likely to be better than phones, but that's not always so. How the different software interprets the data will account for further errors.
  9. OP

    PaulB Guru

    Well to save the effort, I wear a jersey with a big wavy hand on the front so I don't have to take my hand off the handlebars but can still be seen to be greeting them. Doesn't EVERYone have one of those?
    Drago likes this.
  10. Globalti

    Globalti Legendary Member

    Bikehike is accurate and you can go back over the profile so as to see where you suffered most.
  11. welsh dragon

    welsh dragon a permanent vacancy now exists

    I triex looking at that, but couldnt get it to work. Kept saying the http/ wasnt allowed.? I don't think i will bother. :laugh:
  12. Globalti

    Globalti Legendary Member

    Sometimes the website doesn't want to play.
  13. PK99

    PK99 Guru


    0.4% difference on distance well within quoted accuracy for GPS
    5 % difference on timing did you start and stop them exactly simultaneously?
    Different method of measuring altitude - barometric vs map
    Beebo likes this.
  14. Crackle

    Crackle Pah

    The elapsed time is the same on both, 3:30ish, so one probably has an autopause setup and a barometer to do the altitude gain as opposed to working off the basemap. They're both pretty close really.
  15. MontyVeda

    MontyVeda a short-tempered ill-controlled small-minded troll

    I gave up using my phone for GPS tracking after the first time i used it... did ten miles along a very flat canal and it recorded an altitude map with a peak of 110 ft
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