Run tracking discrepancies!

[Makka62a]

So it was W9R2 tonight and I used my Fitbit to track my distance and time as I have ever since I moved outdoors. For a bit of fun l also turned on Strava on my phone but now I confused as it gave me different numbers.

According to Fitbit I ran for 36 minutes and covered 2.73 miles. According to strava I ran for 35:23 and covered 3.08 miles. I can understand the minor time differences due to time to turn on and put in pocket etc but the distance difference is quite large.

Has this happened to other people and can anybody explain it.

Pleasant running everyone!

[UnfitNoMore Graduate]

Just to add to the confusion... one friend of mine at the local parkrun consistently logs the run as 2.92 miles on her Strava even though it was measured as 3.11ish (5k)

A lot depends on the GPS coverage and the quality of the GPSr on the two devices you’re using. Strava maps often have a straight line on them when coverage was lost, which will lose a little distance. Maybe the fitbits GPSr isn’t as good as your phones? A quarter of a mile is a big difference though.

[Makka62a Graduate in reply to UnfitNoMore]

Thanks - I’ll compare the maps and see if I can see any straight lines I rarely Run in a straight line!

[micey2 Graduate]

I use strava and I’ve found it accurate, measured my parkrun as 3.1 miles which of course is exactly 5k. Can’t speak for a Fitbit as I’ve never had one just as well I think I’m confused enough 😂😂

[Makka62a Graduate in reply to micey2]

I’m planning to do a park run soon so I’ll try both there and see what happens

[AgingMetalHead Graduate]

Yes gps discrepancies can be quite large. On my phone I need to make sure any power save / battery save mode is switched off during runs otherwise gps becomes very inaccurate.

[Makka62a Graduate in reply to AgingMetalHead]

I used to use NRC but I stopped because of that problem

[Running_Giraffe Graduate]

I did the same thing last night just to compare and Strava gave me 3.86km and my wrist tracker 4.02km I also had on Relive which gave me 3.86km too. I'm going to try all 3 again for R2 and R3 of the week and see if it continues to give the same output

[Makka62a Graduate]

Keep us updated - I’m now curious about this !

[MarkyD Graduate]

Of course both devices have gps. But there are different gps services. The original satellite constellation was called GPS (hence our name for the system) but the accuracy was limited for civilian us. I don’t remember the accuracy, but 10 meters comes to mind. Subsequently a new service called GLONASS was introduced, with greater accuracy.

Accuracy is important with gps, and for run tracking, the sample rate too. Imagine that you are on a windy track. The gps is sampled every second, and is accurate to 10 meters. All the watch can do is draw a straight line between your last know points, and this reduces the actual distance that you ran.

I believe that some Fitbits do not have gps and rely on step counts. Again the watch only knows your stride length from knowing your height, and this stride length is usually a walking estimate. At the end of the run the watch calculates number of steps x stride length for your total distance. Since the stride length is wrong, the distance is wrong. My Fitbit from 5 years ago had a calibration feature.

[Makka62a Graduate]

That’s an interesting thought. Both devices are GPS. I don’t have access to a track but I can certain run round the block a few times and compare.

I hadn’t thought about signal loss. I had one of the first Garmin GPS devices 15 to 20 years ago and used to run a loop through the woods as part of my run and it never measured it because of the trees. Took me 6 months to spot I was running a lot further than the device was telling me !