Garmin Fenix 5S Warning

Nemo Brauch

If you are thinking about purchasing the Garmin Fenix 5S, I would highly recommend you reconsider (or at least hold off until some dust settles).  I have been using the 5S for a month now and have found the GPS accuracy is sub par compared to my 920XT. Specifically, the 5S records roughly 1 tenth of a mile extra on every mile, and that adds up rather quickly. My rides/runs are all at the beach (flat, strait, no trees, and no buildings higher than 4 stories). So getting a good GPS signal isn't (or shouldn't) be an issue. I have been using the 920XT on the bike simultaneously and that's how I noticed the issue. My bike route happens to have mile markers on the road, so on my last ride I hit the split button on each watch to record the difference. Sure- I might hit the button a little early or late each time, but it shouldn't be a whole tenth of a mile off. You can see the results in the Connect files available at the below links (FYI- I'm using GPS Only on both watches). Searching through various forums and blogs it looks to me like I'm not alone with this problem. Sadly, I probably would have been better off with the 735XT.
https://connect.garmin.com/modern/activity/1813943648
https://connect.garmin.com/modern/activity/1813944937

Al Truscott

Are you using the GLONASS option? Maybe you could blame the Russians. Or if not, you could blame our own government, a popular game nowadays.

Seriously, since I use my Fenix 3 for EVERYTHING, I checked its accuracy. I routinely ride with a PowerTap Joule GPS as well as my watch. Less than a 1% difference. I run on a trail with 1/2 mile markers... much less than 1%. So the 3 remains a reasonable choice despite the 5's travails.

Nemo Brauch

Not using GLONASS.  GPS with "Smart" settings- which, according to the Garmin folks is the option they would recommend.  The Fenix 3 is just too big for my little wrist (even the 5S is a tad big), which is why I mentioned the 735.  I've reached out to Garmin for support and the have asked to see the original files.  I will report back when I get an update from them.  But for now, their response was as follows:

"Looking over the information, the track information seems nearly identical, My theory is that your Fenix 5s may have every second recording enabled. When this setting is enabled the device lays several more track points in an effort to help you collect more specific data. However, as a trade off if the device records this often, it is much more prone to be affected by what we refer to as GPS drift.

GPS Drift is something that can affect every device, but tends to show more on modern devices with high sensitivity receivers and fast recording settings (such as every second recording). Connect does its best to cut the extra unneeded data points, but it may be that the distance held the inaccuracy. 

The two GPS tracks seem nearly identical, so we will need to take a deeper look at the original files, but the unit itself does not seem to be malfunctioning. "

Derrek Sanks

Try enabling GLONASS.  That increases GPS accuracy but uses more battery.  Also, according to DC Rainmaker, 1 second recording should be used as it's more accurate than the Smart setting, so Garmin's comment about GPS drift is interesting.

Nemo Brauch

So, here's something interesting to add to the equation.  I did a run/walk (3' walk/ 1'run) today on the same marked road and I wore both watches.  This time they matched each other for the whole course almost exactly.  So perhaps there's something about the speed factor.  Total 6 mile route was off by less than 3/100ths.

Ill try GLONASS on my next ride out of curiosity if nothing else.  But seriously, I've got practically 180 degrees of unobstructed sky to work with so there shouldn't really need to be a whole lot of extra software help needed to find or accommodate for the lack of satellites.

Nemo Brauch

Rode the same route today with UltraTrac turned on.  This made no difference.  The Fenix 5S continues to record mile splits (and the total ride) longer than they should be.  

Nemo Brauch

Mystery Solved!!

I've done a significant amount of riding with various different settings and on various different bikes.  I've finally discovered the issue and wanted to report it back so that others might be able to troubleshoot this problem if they run into it.

The Fenix 5s was paired with a PowerTap Wheel.  It appears that the Fenix 5s takes the speed/distance from this device rather than using the GPS.  When I first paired the PowerTap it did not ask me for wheel circumference (or if it did, I don't recall and must have selected "auto").  The PowerTap is on a 650c wheel.  It seems the Fenix 5S thought it was a 700.  That is what was causing the problem and why it wasn't seen on any of my runs.  

I removed the PT sensor from the Fenix, then re-added it and was prompted to enter the wheel size.  Voila, everything is groovy.  

Mike Neas

Thanks for the troubleshooting and the solution Nemo.  I was beginning to worry about my Fenix 5's credibility:-)

Patricia Rosen

ah hah!  you should buy my awesome B12 with 650 wheels then....  I use 700's now so trying to sell old bike...
now that your device is working with a 650 you could use my groovy old ride