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Discrepancies between Cyclemeter and Strava Distances

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  • December 14, 2014 at 10:18 am #22858
    penguin116

    Apologies if this has already been covered elsewhere, but I’m really struggling with this.

    I have been using Cyclemeter (Elite version) on my iPhone to record my rides for a few months now, then uploading them to Strava once I’ve got back home. I then noticed a couple of weeks ago that the distance covered according to cyclemeter was significantly higher than on Strava once I’d uploaded it. For instance, yesterday, I went for a short 16-mile spin. At the end of the ride, cyclemeter reckoned I’d covered a smidge over 20 miles, and when I uploaded it to Strava it said I’d covered 16.3 miles.

    I presume that cyclemeter is using the input from my speed sensor rather than the GPS of my iPhone. I’ve got a Panobike Cadence and Speed sensor on the bike, and I’ve put in my wheel circumference into cyclemeter (2099mm) which I’m pretty sure is correct – 700c rims with 622-23c tires. I don’t think that there’s any other settings that need to be configured.

    When I look at the detail of my speed during the ride on cyclemeter, I top out at 40mph (which I think is frankly unrealistic) and on Strava it says it’s about 33mph (which seems a lot closer to the truth 🙂 although I suppose I could be doing myself a disservice 😀 ).

    So I’m confused as to what’s going wrong here. Any help would be much appreciated.

    Thanks

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  • December 23, 2014 at 1:37 pm #823409
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    the_jm

    I typically find about 2%
    I typically find about 2% difference in distances, which is pretty consistent. A 100km ride registered as 98 on Strava and a 103 miles registered as 101. I have two of these sensors on different bikes and the results are near enough identical. If you’re getting speeds and distances that are between 25%-35% out the odds are it is the cadence magnet that is the cause.

    December 23, 2014 at 11:21 am #823407
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    penguin116

    Success! At least I think
    Success! 🙂 At least I think so. Looks like the cadence magnet was the source of interference on the speed sensor.

    A quick 15 mile blast (according to Cyclemeter) with top speed of 30.2mph uploaded into Strava and it’s come back with 14.75 miles and top speed of 30.0mph.

    Hoping to go for a longer ride tomorrow, so we’ll see if this extrapolates to wider inaccuracies, but I’m pretty happy with the change.

    December 18, 2014 at 4:39 pm #823405
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    penguin116

    Thanks for your advice
    Thanks for your advice the_jm. I’ll have a crack at this over the weekend and see what happens.

    December 18, 2014 at 3:43 pm #823403
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    the_jm

    It should be pretty easy to
    It should be pretty easy to check. Get on the turbo, top gear, pedal up to 100 rpm and see what speed. Assuming 50 on the front and 11 on the rear you should see around 35.8mph. For any other ratio 7.87 * front/rear will give you a good enough approximation of the speed. If that is correct, you need to make sure cadence is being counted correctly. Count rotations for a measured time to check that.
    It could also be poorly placed magnets, the magnet on the crank may be too close to the speed sensor, or the magnet on the wheel might be too close to the cadence sensor. (Edit: Looking at the differences you are getting I would say this could well be the problem. Your cadence magnet could also be registering on your speed sensor, try adjusting the position of the magnet realtive to the sensor)

    December 18, 2014 at 2:14 pm #823401
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    penguin116

    Aha. It didn’t occur to me
    Aha. It didn’t occur to me that it could be the sensor that’s actually faulty. Maybe it’s time to use Wiggle’s 365 days returns policy.

    December 18, 2014 at 12:11 pm #823399
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    the_jm

    penguin116 wrote:Abvio

    penguin116 wrote:
    Abvio suggested that the Wahoo was the better sensor to use, but being tight-fisted (and resident in North Yorkshire 😀 ) I went for the cheaper option. Should have shelled out the extra 15 quid (or whatever the difference was) and opted for the Wahoo. 🙁

    I’ll play with the settings for the wheel diameter and see if I can get a more accurate approximation for my speed and distance.

    I too am from North Yorkshire and tight-fisted, hence I have the Panobike sensor too. The speed sensor seems pretty accurate with mine, riding in a bunch with others with various sensors and we all seem to be reported within +- 0.2kph of each other. It could be a QC issue though. I also do not get such big differences between Strava and Cyclemeter, Strava is pretty much consistently about 2% less than Cyclemeter records. This is annoying when you’ve just completed a metric or imperial century and Strava says not!

    December 17, 2014 at 5:35 pm #823397
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    giobox

    GPS, while often very good at
    GPS, while often very good at giving you an x,y coordinate, is really bad at calculating altitude. If you upload a ride from the Strava app, Strava uses map data for the x,y point of your ride to get the altitude, completely ignoring the GPS. This generally results in way more accurate elevation for a given ride.

    If you don’t use the Strava app and use your own dedicated GPS, this is what the “correct elevavation” button in Strava does – replaces your GPS unit’s altitude numbers with values from their map data. If you have a good quality GPS it will have an altimeter built in to calculate altitude instead of using the GPS value. This is what the Garmin Edge 800/810/1000 do for example.

    December 17, 2014 at 1:50 pm #823395
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    andyp

    fenix wrote:
    Not that

    fenix wrote:

    Not that strange. I just record it as a session – but its not miles.

    I could set the resistance down low and generate lots of junk miles.

    Low resistance? Like…bimbling around a flat route in zone 1. Or a big downhill. Also ‘junk miles’, presumably, and stripped from your mileage?

    December 17, 2014 at 9:58 am #823393
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    le Bidon

    fenix wrote:andyp wrote:le

    fenix wrote:
    andyp wrote:
    le Bidon wrote:
    turbo sessions shouldn’t contribute to your yearly total! ;)

    This is quite literally the strangest cycling ‘rule’ of all time. Freewheeling down a big hill counts towards your yearly total, but an hour at FTP doesn’t?

    Not that strange. I just record it as a session – but its not miles.

    I could set the resistance down low and generate lots of junk miles. Its a great training session – but its different to miles. usually better in fact – so keep the two seperate.

    Exactly! Whether the “miles” are better or worse they are different and ought to be kept separately.

    December 17, 2014 at 9:13 am #823391
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    penguin116

    Abvio suggested that the
    Abvio suggested that the Wahoo was the better sensor to use, but being tight-fisted (and resident in North Yorkshire 😀 ) I went for the cheaper option. Should have shelled out the extra 15 quid (or whatever the difference was) and opted for the Wahoo. 🙁

    I’ll play with the settings for the wheel diameter and see if I can get a more accurate approximation for my speed and distance.

    December 17, 2014 at 3:15 am #823389
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    fenix

    2099 sounds about right – but
    2099 sounds about right – but what PSI and weight are you ? If its low – then surely that would reduce the figure and increase your milage ?

    I’d put in a silly figure – half or double it to see if that is where the reading is being calculated.

    Strava is accurate for me – it always compares well to my Garmin anyway.

    So I’d go with that in future.

    December 17, 2014 at 3:10 am #823387
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    fenix

    andyp wrote:le Bidon

    andyp wrote:
    le Bidon wrote:
    turbo sessions shouldn’t contribute to your yearly total! ;)

    This is quite literally the strangest cycling ‘rule’ of all time. Freewheeling down a big hill counts towards your yearly total, but an hour at FTP doesn’t?

    Not that strange. I just record it as a session – but its not miles.

    I could set the resistance down low and generate lots of junk miles. Its a great training session – but its different to miles. usually better in fact – so keep the two seperate.

    December 16, 2014 at 7:02 pm #823385
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    Tintow

    I use Cyclemeter and Strava
    I use Cyclemeter and Strava with a Wahoo Blue SC and the readings are always pretty similar – never identical due to the issues described above but very close.

    December 16, 2014 at 2:27 pm #823383
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    Man of Lard

    Even if you were at sea, it
    Even if you were at sea, it would depend on the state of the tide.

    December 16, 2014 at 12:07 pm #823381
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    andyp

    gdmor10 wrote:from what I

    gdmor10 wrote:
    from what I understand GPS doesn’t do altitude very well, I remember being out sailing once and the GPS on the yacht said we were 3m below sea level – am pretty sure that was not correct.

    Depends if you were on the sea or not. Otherwise it’s quite possible.

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