When is a 3 mile run not a 3 mile run?

[Steady_Stevve]

This morning I completed my second charity run. It was a nice easy run which I had used mapmyrun to measure. I was really surprised when I finished to find I had only done 2.8 miles according to Strava.

Has anyone else had the same problem? Which is the more accurate?

[Irish-John Graduate10]

I am presently surrounded by an "ad hoc"

Marathon Running group, all much younger than I and very tech savvy.

They have Fitbits, Vivo-somethings, Garmin's, phone apps and so forth....and rarely do they all agree on distance

I prefer checking old fashioned maps when it's really important to me - like in a Virtual event - that I actually cover the the required distance. My borrowed Vivo-something last week differed by four tenths of a mile over 26.2 on a trail that was measured (I checked lol) physically using a Surveyors measuring wheel back in the day

Four tenths of a mile isn't a lot so I do appreciate the marvel of technology - but basically I look at it in black and white. Either a thing works or it doesn't, so for me the gadgets are fun but not trustworthy to really be "practical"

[Steady_Stevve in reply to Irish-John]

Thanks, that's helpful.

[Tasha99 Graduate10 in reply to Irish-John]

Definitely not all more tech savvy nor younger than you over on the marathon forum IJ 🤣

[Irish-John Graduate10 in reply to Tasha99]

😁

[CBDB Graduate10]

Oh that path looks so gorgeous to run on 🤤🤤.

I normally use Runkeeper and sometimes NRC, and they often differ. Annoyingly when I use pocket-track in Runkeeper (basic tracking without having to launch RK) it sometimes suggests that I have walked ca 1km more than I ran. Correcting the type of exercise from walking to running then corrects the distance, which always feels a bit humbling! 🤣🤣

I don’t mind the inaccuracies, and I’m not sure what tech is most accurate in terms of distance: smartphone, watches or chest belts. For Heart monitoring chest belts seem to be perceived exact, but not sure about distance.

[Steady_Stevve in reply to CBDB]

Thanks that's helpful for future reference.

[Tasha99 Graduate10]

Get a garmin 😍

[Magellan Graduate10]

Unless you run in a straight line or very nearly straight, the map is more accurate than the GPS. This is because the map uses the exact roads and tracks that you feed it, but the GPS uses data points every few seconds. Whenever you turn a corner or round a bend, there's a good chance that the data points that are sent won't reflect your complete journey.

Imagine you're running in a circle, and your phone sends six data points to Strava. Strava will then plot for you a hexagonal run, inside the circle you actually ran, and as you can imagine the hexagon will be a shorter distance than the circle.

I have a Garmin watch, on its normal setting I can see corners cut on most of my runs, so that it thinks I've run through people's gardens or farm buildings. It manages long straight lines fine, even to the point of putting me on the correct side of the road when I cross, although it tends to make me cross diagonally even though I cross roads properly. It also has a setting that gives near perfect accuracy because it takes a data point every second, but that wears the battery down faster.

[Steady_Stevve in reply to Magellan]

Thanks, that all makes sense. A perfect explanation.

[KevinFG Graduate10]

What Magellan says, often I get a point at a sharp turn where the GPS decides my speed jumps because of the GPS assuming you take a direct route between positions, should not happen if you are road running though.

[Steady_Stevve in reply to KevinFG]

Thanks. I understand the issue now.

[HeavyFoot Graduate10]

It’s a pain.

The Health app on my iPhone over-reads distances by 10-15%. Its “flights risen” calculations are often laughable.

I used to trust my SportsTracker app (like Strava) more, until recently when it recorded 2•5 hours for a hike which took 4 hours and under-read the distance by about 3 km.

[Steady_Stevve in reply to HeavyFoot]

Wow. Thanks for the heads up on this.

[Jerry_Hatrick Graduate10]

I’ve given up with recording distances using GPS on my phone. My regular running route is circuits around some local playing fields which involves about 8 sharp turns each 1k lap. I measured the course using Google Earth Pro and the Ordnance Survey app, both of which are very accurate. Because of the way GPS samples the run and joins up the dots it appears to cut the corners by about 4 or 5 yards a time, so after about 7K it is about 200 to 300 metres short, which is enough to mess up any statistics if I wanted them.

I’m no expert but, there are quite a few factors that affect the accuracy of different GPS devices and they are not quite as consistent for measuring distances as some people imagine. On a run in the open with few changes in direction the problem should be less significant. but it always seems to under report to some extent. As suggested, it’s best to measure your route with a good mapping tool first.

[Steady_Stevve in reply to Jerry_Hatrick]

Thanks, that's helpful. Others have reported the same problem with GPS tracking. It is good to know the limitations of any system.