Tracking Your Run – GPS Watch or iPhone?

Tracking Your Run – GPS Watch or iPhone?

Given the rapid advances in phone technology, we decided to test if your iPhone could really give you the same accuracy as a GPS watch on the trails. Can you really justify that extra toy or will your phone give you the same result without blowing your budget?

To be fair, your watch does have some great features that a phone simply can’t replicate. Rather than being an all-purpose communications and entertainment device, a GPS watch is designed with a specific use in mind and generally does these well. It provides sport data clearly in an easy-to-access wearable with peace-of-mind durability. Even with the new iPhone X being IP67 splash, water and dust proof, that screen is always a risk when out running, both for random falls and operating with sweaty fingers.

GPS watches also have the advantage of longer battery life (with various options to increase up to +50 hours) and the new integrated optical heart rate monitors on watches are also much more accurate these days, and can be a great feature when trying to pace your effort.

Finally, for mountain goats who need to know their elevation and vertical gain, a watch’s barometer allows much more accurate measurement than triangulating with four or satellites then linking that position to a basemap database. On a hill contour or cliff edge, for example, if your location drifts by as little as little five to ten metres this really vary your elevation readings, giving you credit for vert you haven’t earned! It’s interesting to note that today’s iPhones do have a barometer in the bottom left vent, however, most apps (including Strava) don’t use them.

But ultimately, it’s about accuracy and we want to know if a phone GPS will give you as good a result as a running watch – so we tested the Garmin Forerunner 935 against an iPhone 7-Strava combo on an easy paced run over straight and windy road and trail, and this is what we got.

Garmin – 15.8km and 707m D+

iPhone – 17.8km and 1,208m D+

The difference between the two - Garmin in blue and iPhone in red - surprised us, with the iPhone recording an extra 2.0km or 13%. On the larger map, iPhone seems to deviate in a number of places, both on road and trail, particularly where the course turns sharply.

Zooming in for a closer look at a shorter section on the Wilson Trail, it's clear that the iPhone is having some serious issues. The iPhone route is broadly correct but oscillates left and right of the actual route, adding significant distance beyond what was actually run. 

This same issue is apparent in the elevation profile of the iPhone, where flatter sections are recorded with significantly more variation as the iPhone drifts. While the elevation profile is broadly correct, the iPhone can be out by up to 50m at a time, and adds significantly more false elevation changes over the course of the run. Amazingly, the total recorded elevation was 71% more than recorded on the Garmin.

Of course, we can't apply these findings to all phones and all GPS recording apps, but it does give pause to anyone considering replacing their GPS watch just yet. If you just want a general diary of your runs, the iPhone-Strava combo might be "good enough" but those seeking accurate recordings might need to stick with their watch and Gone Running have a great selection available here.

Credit: Asia Trail

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