Fenix 6 Pro GPS accuracy problem

I checked both activities. So first, GPS is fine. Both GPX tracks have the same length of around 8.9 km. 

There seem to be two factors that cause the wrong distance. At first, the pace seems to be incorrect or inaccurate. Second, Garmin seems to try to measure the distance using this incorrect pace. E.g your pace for the first lap is 9:36 and the 1 km mark is exact at 9:36 min. Also the time between 1km and 2km marker corresponds exactly to the pace of the second lap. Of course this is what we would expect, but only if the pace is correct. It seems like Garmin is sourcing the pace data not anymore (or at least not mainly) from GPS, but from the accelerometer data from the watch or the chest strap. Or they are using GPS but ate calculating it incorrectly for some reason. On your first activity, the 1km marker does not perfectly correspond to the lap pace. So here pace and distance are 'disconnected' from each other. 

What is also weird is that I do not see this behavior on my runs. The differences that I noticed are that I do not use laps, I use running, not trail running and I use a HRM run (or no chest strap), not a HRM pro. 

I have done 1000s of miles with a Fenix 6 Pro and other watches and i just do not see short distsnces from the F6 Pro (usually within 0.02 or 30 meters)

If people are seeing massive distance under reporting it feels like a faulty device to me, especially when people are talking about 20% errors. 

Interestingly though when I run with my brother-in-law my distances are longer than his - my F6 and F7 agree very closely, but he comes up shorter by about 1% when we are side by side. 

Thanx!! Interesting... If I say that I am using running, laps and an hrm pro.... I'll try NOT using the hrm pro data and see what happens.

It depends a lot on terrain. There is way more difference when running on wooded mountain slopes. For example there is a popular route in my area which is officially 20.4 miles. Fenix 6X measured it as 19.35 miles. Fenix 7X - 20.2 miles. 

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silentvoyager said:

There is way more difference when running on wooded mountain slopes

I just do not see it, I live in the most mountainous area of the UK (Lake District), and have a forest on my doorstep (Whinlatter)

The parkrun there has 700 feet of elevation over 5k and I always measure about 3.11-3.13 - never short. It's basically impossible to run it short (or long) as these are super narrow paths often not more than 3 feet wide.

What I do see when I go under tree cover with a f6 is that the track 'wobbles' much more, but as it wobbles left and right it seems to cancel itself out the the distance comes out OK.

Obviously when we are talking about 'gps accuracy' and talking about wooded areas is not great context for gps accuracy anyway, because the watch is going to be be using accelerometer input when signal quality dips.

I have done a ridiculous amount of testing on this - including with calibrated Stryds and using Pace / Distance from the HRM Pro, and I really struggle to get my F6 Pro to report short

https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/301347/hrm-pro-fw-8-80-or-plus-for-improving-distance-and-pace-related-problems-for-outside-running-on-the-f6

My feeling is there is some other factor here we are missing that causes a small minority to have this issue - I think it is plausible that a bare titanium Fenix 6 which I have possibly produces better tracks than a Fenix 6 stainless steel or DCL cover bezels? It is also possible that the larger Fenix 6x being heavier 'bounces' more on the wrist which may be contributing to irregular accelerometer inputs? This is just spitballing really, but I think there is some nuance here that is a contributing factor. 

@5135968 I just checked. My HRMPRO is on "pace and distance always". I can very well imagine that this is the issue that I have, since I have recently started all kinds of pace and cadence trainings (running at 195 cadence instead of usual 165, and changing paces during the run).
I can imagine that this is very "confusing" for the HRM Pro, so I'll check today with "pace and distance only indoors"... so let's see. I'll revert back to you guys asap

Adding another data point to this thread - F6S Pro here - I have been obsessively comparing distances since I got the watch in early 2021 and found that:

• Run activities are usually a little bit short (a marathon might be 200m short, for example, but this applies across all distances) vs the same gpx where distance is re-measured by e.g. Strava, Runalyze, or a GPX desktop application
• Trail Run activities are usually worse (a marathon was 1.2km short; again this applies across all distances).

I recall someone on this forum analysing a Trail Run .FIT file and noticing that the reported distance was always shorter than the distance between the two GPS points, which would explain what I observed.

FWIW I run every week in a mix of trails, forests, mountainous terrain, road, city streets and running track, and I only noticed it being worse in cities, for obvious reasons.

BUT... since updating to 24.10, the gap in GPS vs Garmin distance is now much reduced. So much so that I will stop correcting distance, both for Run and Trail Run traces, if this is consistent.

MickyWicky said:

Trail Run activities are usually worse (a marathon was 1.2km short; again this applies across all distances).

Interesting! 

I've have not observed this - this run is from the Maverick Adidas Terrex 25k run in Grasmere, UK and the tracks from both the Fenix 6 and Fenix 7 are basically identical with only 0.04 miles difference between both devices.

The GPS tracks are so close, in the overview is just looks like one device

And zooming into the track under tree cover...

Distance recorded from both...only 60 meters (0.04 difference) - and the Fenix 6 is actually 0.04 miles LONGER here!

This is literally all I do, so I'd think by now I would have seen the problem!