Recently, I decided to upgrade from my Garmin Vivoactive 3 Music. The Garmin’s replacement is the Coros Apex multisport GPS watch. I won’t share too many insights about the switch in this post (that’s coming later). This post is meant to save others the trial and error of figuring out why two GPS watches would record distances so differently.
The answer is so simple you just might slap your palm to your forehead. But first, a little context…
When I got my new Coros, I planned to run and go for walks with both watches for a while. I did this for two reasons: (1) to make sure the new watch was measuring accurately and (2) because the Coros interface is so different, I wanted a backup GPS file while I was getting used to the new watch.
Right away, I noticed the watches were getting very different readings for elevation and distance.
For a route that’s just over 5K, the Garmin was recording 3.33 miles and the Coros was recording 3.44 (a difference of about 0.11 miles). For that same run, the Garmin recorded an elevation gain of 69 feet while the Coros recorded a gain of 112 feet.
Over the next week, a few other short runs (ranging from 2-4 miles) also had the Coros recording distances of about 0.10 miles more than the Garmin. It was perplexing, frustrating and worrisome. And because the watches were recording the same amount of time for these distances, the Coros was making me seem much faster.
Running distances of 2, 3 and 4 miles but always being off by about the same 0.10-mile distance, meant something was wrong. Because both watches are considered to be accurate by multiple reviewers and both Garmin and Coros make great quality GPS watches, I knew it had to be my user error.
So, I started digging into the settings more on the Coros Apex. If you make the switch from Garmin to Coros, you’ll notice the Coros has a lot more settings tweaks with very little explanation for what will actually happen if you start changing things. (Yes, the watch comes with a manual. But it doesn’t explain why you’d tweak a sensor’s settings.)
Not all satellite systems are created equal
Digging through the settings was the key. It was there I realized the two watches were measuring distance differently.
By default, the Coros Apex records distance using GPS and Glonass. Recording with both is supposed to yield a better result on challenging terrain, but if you’re running on paved trails in a city (like me) the Glonass probably isn’t necessary.
My Garmin Vivoactive 3 Music was recording with GPS only. (Though, I discovered I could’ve turned on GPS + GLONASS or GPS + GALILEO options at any point in the past two years.)
Switching my Coros to GPS only has the two watches recording distance almost exactly the same when I run. And now I know to switch my new watch back to GPS + Glonass the next time I go for a hike in a state park or on a mountain.
Here’s how to make the settings tweak for Coros Apex users: Go to settings, then choose More Settings and go into the GPS menu and select GPS Satellite Location Data. After making the new selection, you should see an alert on the screen letting you know that syncing your watch to the Coros app will keep your GPS satellite data up-to-date. Hit the back button a few times to get back to the watch’s main screen. And that’s it!
About the elevations being off
What about the elevations being off? Well, they’re still not identical for me. But I have got the two watches recording much closer to the same elevation.
Fortunately for me, both watches use a barometric altimeter to detect air pressure change and calculate elevation changes (from floors climbed to more general elevation data while recording a GPS activity). So, I know the two devices are recording the information the “same way.”
My “fix” for the elevation discrepancies is in the Coros’ settings. Under Sensors, in the Barometer menu: I switched from the default Sea-level Pressure to Station Pressure. If you’re curious what the difference is, here’s a nice explainer from the National Weather Service.
On extremely windy days, the Coros’ elevation does seem to be a bit more influenced than the Garmin. Though, Coros says on its site that this might be the case.
