UKH

 Hi guys. So a few months ago, I bought a used 66i Garmin. I bought it really to get me through a night section of a 100 mile event. I used it a few times before hand to get used to it BUT in probably 4 out of the 10 times I have used the device, when downloaded to Strava, the mileage shows quite a bit less than the distance I have actually walked. The frustrating thing about my walk at weekend was that it was a one off for me and whilst the Garmin still shows I did 102 miles, when downloaded to Strava its only showing 60 miles (ie a long long way short). I am lead to beleive this is a know "glitch between Strava and Garmin so apologies if this has been bought up on here before. Why does this happen and can anything be done about the problem on my next walk ??

Whilst I can't comment on your specific issue between Garmin/Strava, the file produced by a fitness device is usually a GPX or FIT file and is essentially just a text file with a load of GPS(GNSS) information in it.

There are plenty of online tools (Google GPX/FIT editor/fixer) you can load this file into, and see if there are any obvious problems. I vaguely remember using one a few years ago for a similar issue that essentially had a "Fix" button that automatically identified and fixed any issue. The resulting file can then be manually imported into Strava.

It might be that the Garmin is on Autotrack, power save mode. That takes a GPS reading every few mins, not every second. If your route had lots of zig zags, it will straighten them out, so it will show as less. Not sure why there would be a descrepancy between the device and the app.

Top tip, if your time is out in Strava, record it as a race. Strava usually strips out any stops, recording only moving time. Race mode is from start to finish.

Fit is a binary format, it’s not a text file with gps stuff in it.

Yes you're right it's not an ASCII file, I had written my initial response solely around GPX files before remembering that Garmin actually stored them as encoding files (with GPS stuff in).

The rest of the comment is still accurate, in that there are plenty of tools to read/edit/fix them.

I think your GPS device records in Inreach mode every 10 minute or 30 minute (energy saving) intervals to file and not every few seconds like a watch/the displayed distance so there will be a considerable reduction in points and this will explain the difference. We have an inReach device and it is very clear on that when the file is opened in the inReach web app. It looks like Strava is getting that data. However there must be data with all the information on as you will be able to see that on the screen. On my old 64 you could plug in the GPS and copy the files onto a computer and this would allow you to see what you have and then upload them. HTH