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Discrepancy between MapMyRide and Strava

bungle73bungle73 Posts: 735
edited March 2016 in MTB workshop & tech
TBH, I'm not exactly sure this is the correct location to post this, but here goes......

I mainly use MapMyRide, but recently the app has started crashing on me (it's an iPhone 4 so I can't upgrade to the latest version), so this morning I decided to track my ride with the Strava app instead, then export it and import into MMR.

This all worked fine. However, I've noticed something most odd. On Strava it gives my max speed as 20.4 mph (which agrees more or less with my cheap Chinese cycling computer). But for some reason MMR is giving my max speed as 22.3 mph, even though it is the same data!

What's going on? :?

Posts

  • The RookieThe Rookie Posts: 27,747
    GPS can through up the odd oddity, you only need a tiny error when travelling fast to create a a blip and a higher peak speed, if you look at the trace you'll probably see a meaningless and impossible spike in speed.
  • RockmonkeySCRockmonkeySC Posts: 15,247
    GPS isn't all that accurate on twisty trails. The app fills in some of the gaps. These two apps obviously fill in the gaps differently.
    It could be 20.349 compared to 20.350. Just very borderline.
  • bungle73bungle73 Posts: 735
    The Rookie wrote:
    GPS can through up the odd oddity, you only need a tiny error when travelling fast to create a a blip and a higher peak speed, if you look at the trace you'll probably see a meaningless and impossible spike in speed.
    Nope. I can't see anything like that. But then difference between the two isn't that great.
    GPS isn't all that accurate on twisty trails. The app fills in some of the gaps. These two apps obviously fill in the gaps differently.
    It could be 20.349 compared to 20.350. Just very borderline.
    It wasn't twisty trails, just a few miles of roads.

    There was a point new the beginning where there is a huge jump between two locations, because I was having a slight difficulty with the app because I hadn't used it before. But that is way before the anomalous section, so I don't think that would have caused it.

    Thanks for the replies. I guess it's just one of those things.

    There is something else that is rather odd. The above was with importing the GPX file. When I tried the TCX file to see if made any difference, it came out with some silly top speed of 2000 mph, or something that that! :?
  • I would use MMR and Strava as a basic but crude tool. They are not 100% accurate, depending on where you place your phone can give false information.

    Use them for what they are, they take average readings and put it into a simplified graph that you can read.

    I wouldn't say it is odd at all, as there are so many variables with using either.

    Just treat them like a rough guide.

    Eg, you may use one or the other and do the same route and do it in the same time but the apps have a discrepancy, even within themselves.

    In final too many variables, just use them as a average.
  • .blitz.blitz Posts: 6,588
    As above the they're a rough guide. Repeatable maybe but not accurate. Did a ride yesterday that the phone and Garmin and mapmyride disagreed on. The straightlined sections where one or the other or (both) had lost the signal could be seen when zooming in. Tree cover really kills them
  • As above, these things only sample your position every X seconds, which makes them inherently inaccurate. I mean.. come on they missed your sprint at 2000mph!

    Seriously, for any instantaneous reading, use the bike computer / speedo. Come to think of it, even when road riding I have a pretty well calibrated Polar computer, and that always disagrees with MMR. So on a mountain bike, unless you're always riding fire-roads / landrover tracks you're going to be worse off.
  • larkimlarkim Posts: 2,287
    All of the online services which show GPS traces interpret / smooth / error correct the data in different ways, and some account for stopping / pausing differently than others too.

    It could be that MMR simply aquires top speed by the S=D/T equation relying on only two data points, whereas Strava requires the D to be measured over a couple more data points etc.

    I use at least four different running websites to report my GPS data from runs (each has something strong about it that I like) and they invariably report different distances / top speeds / average paces. The differences are never material, and I just accept that, for example, Strava rounds distances down (e.g. 4.97 becomes 4.9) whereas others round in a more traditional way.

    It's not as if any of us are using these sites as evidence of world records etc are we?
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
  • mattyfezmattyfez Posts: 638
    Top speed is pretty meaningless though, it's all about average speed! Which is more accurate anyway as there are lots of points of reference.
  • bungle73bungle73 Posts: 735
    mattyfez wrote:
    Top speed is pretty meaningless though, it's all about average speed! Which is more accurate anyway as there are lots of points of reference.
    I like to know how fast I've gone! :P
  • larkimlarkim Posts: 2,287
    Then a traditional cycle computer is the best way to get an accurate reading I'm afraid. So long as it is properly calibrated, there's little that can fool a wheel into rotating faster than it actually does.

    Or alternatively, just take the highest figure that the GPS says, and trust that and don't worry about the inaccuracies. Unless you're looking to break the WR, no-one else will really care!
    2015 Canyon Nerve AL 6.0 (son #1's)
    2011 Specialized Hardrock Sport Disc (son #3s)
    2013 Decathlon Triban 3 (red) (mine)
    2019 Hoy Bonaly 26" Disc (son #2s)
    2018 Voodoo Bizango (mine)
    2018 Voodoo Maji (wife's)
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