Fenix 6X Distance Accuracy

Whether we like it or not GPS measured distance can be up to 10% off depending on the overhead cover and any number of other reasons. That said, my F6 Solar Pro is usually well within 5% of an accurately measured 5km parkrun course (less than 50m either way actually) and in reasonable agreement with others on less accurately measured runs over longer distances. However, without seeing the range of measurements from the other watches referenced here, it's much harder to determine where the fault (if there is one) might be.

If you are confident that you have done all that can be done to get the best result and are still dissatisfied, then perhaps you might need to be a bit more persistent with Garmin Support. It is of course possible that you might have a defective watch.

Jkaser1965 , do it as I described. Export the activity as GPX from Connect (web) on the computer, and then import this GPX file back into Connect.

What kind of distance difference do you get ?

I think you are definitely on to something bluefish!  I did what you said and it went from 23.83 to 24.87.  Still a little short of what others are getting but I would think this is very acceptable!  I would be elated with 24.87 on a 25 mile loop.

That 25 mile run, was it on trails? I find that Fenix is fairly accurate on open terrain. But when running on trails with a dense tree cover, it is routinely 5-7% short. I was actually testing this by running with Ambit3 Peak on one arm and Fenix 6X on another arm, and I could see that Fenix would keep up Ambit3 Peak on open terrain or on straight sections of trails, but quickly fall behind once trails started making more turns. 

Furthermore, if you import a run recorded with Fenix into some 3rd party web site and look at the distance calculated from the recorded track, the resulting distance would almost always be much closer to the actual distance. For example, you can see that distance if you do distance correction in Strava. So basically, Fenix seems to be applying too much smoothing and negatively impact distance accuracy. 

Fun fact: Suunto 9 used to do the same a couple of years ago, which actually prompted me to move from Suunto 9 to Fenix 6X. At the time Fenix was more accurate. Then Suunto listened to user feedback and fixed their distance calculation algorithm, and now it is far more accurate for trail running. And Garmin seems to have done the opposite, because now the distance seems to be more smoothed that it was in January 2020 when I bought the watch.

silentvoyager said:

if you import a run recorded with Fenix into some 3rd party web site and look at the distance calculated from the recorded track, the resulting distance would almost always be much closer to the actual distance. For example, you can see that distance if you do distance correction in Strava.

I would not call a few hundred meters difference a problem. This from a trail run on Sunday.

Uncorrected

Corrected

And this from a much longer run a couple of years back:

Uncorrected

Corrected

I'm not peddling the Garmin cool-aid but my experience is that the GPS works and is rarely more than a few percent adrift from any accurately measured track. There are differences when compared to other watches but never too much. And since those runs have not been accurately measured it's hard to say which watch is right.

Looking at Old Ghost Ultra pictures, it seems a lot of terrain is pretty open. So it isn't surprising that the distance came up pretty accurate and there wasn't much smoothing. When I did an ultra on an open terrain earlier this year, my distance had matched the advertised distance pretty accurately too.

But here in Pacific Northwest most of the terrain is covered with dense coniferous tree canopy, and that affects distance on my Fenix quite a bit, and makes it deviate from the recorded track by 5-7% or even more.

Just as an example, yesterday I had a relatively short run, but it involved a lot of switchbacks. Distance on my Fenix 6X was 6.37 miles and distance in Strava after distance correction - 6.99 miles. That is about 10% difference. The distance for the same course when I planned it in advance was 6.67 miles. And in my experience the planned distance is always shorter than actual because of the simplified shape of trails. In reality trails are more wavy. The fact that my Fenix managed to measure 5% shorter distance than planned in a map software is an indication of how bad the accuracy is.

OK, yesterday's example was perhaps a bit too difficult for any GPS device. A week ago I ran 30 miles on Pacific Crest trail, which was fairly straight and had zero switchbacks. Still, distance correction had added 1 mile or 3.3%.

This is a debate that can have no end. Others also in the Pacific NW have suggested their difference in distance are acceptable while others do not. The reality is that anything within 10% on heavily forested trails with lots of tight turns is not an unreasonable outcome from a wrist worn GPS watch. 

The examples I've posted are just two of the numerous examples I have going back many years with many different distances in varying terrain and very different levels of overhead cover. I could just have easily picked any of them and been confident that the distances would be within 10% or less than Strava's so-called corrected distance.

silentvoyager said:

The fact that my Fenix managed to measure 5% shorter distance than planned in a map software is an indication of how bad the accuracy is.

It's an indication of nothing other than there is a difference between a plan drawn on a map and the distance recorded by a GPS device.

The main problem is unrealistic expectations.

support.garmin.com/.../

Dr Phil said:

The main problem is unrealistic expectations.

May we not have the same expectations of Garmin as we have of other manufacturers who meet those expectations ?

I would say the main problem is the excessive smoothing of the FIT file compared to the GPX file at Garmin. Other manufacturers manage to meet the expectations. And as Silentvoyager already wrote, the problem was not so big in the beginning. The algorithm of the FIT smoothing is simply not correct.

silentvoyager said:

Fun fact: Suunto 9 used to do the same a couple of years ago, which actually prompted me to move from Suunto 9 to Fenix 6X. At the time Fenix was more accurate. Then Suunto listened to user feedback and fixed their distance calculation algorithm, and now it is far more accurate for trail running. And Garmin seems to have done the opposite, because now the distance seems to be more smoothed that it was in January 2020 when I bought the watch.

THATS the Problem.