Tracking running, cycling and other workouts is fun because you can see how much you’ve improved (or, in my case, failed miserably to improve). To be effective, you must get the most accurate GPS results. A 4 or 5 percent error can be the difference between an average run and a personal best.
How GPS Works
The Global Position System (GPS) is a very complicated setup. There are 24 satellites (plus some spare parts, at any given time) orbiting about 12,550 miles above the earth every 11 hours and 58 minutes in one of the six different orbital planes. That means four satellites per orbit.
They are so scattered that there are always at least four satellites overhead, everywhere on Earth. More often, there are six or eight overheads. GPS satellites constantly transmit the exact time, orbital position, and other constellation status, which is the information that makes GPS work.
The ground control network is manned by the U.S. Air Force, which coordinates everything and ensures the GPS network remains accurate.
Then, of course, there is your receiving device. It collects signals from all connected satellites and uses the info they broadcast to calculate your position as accurately as possible. If all goes well, the results will be accurate to within about 30 feet.
However, not all GPS receivers are created equal. Satellite signals are not very strong and can be blocked by hills, tall buildings, or even tree canopies and cloud cover. A more powerful receiver can pick up a fainter signal and possibly even connect to more satellites.
Kinda crazy this is the system I use to track my easy 10k Saturday mornings around my local park.
Leave Your GPS Locked
GPS was designed for accuracy, not speed. It may take a few minutes for the receiver to lock into the four (or more) satellites required to be able to calculate an accurate position. This is why apps like Google Maps are a little cheating.
While most smartphones have an actual GPS receiver, much of the positioning is done by Assisted GPS (at least until they get a GPS lock). This triangulates your position from nearby cell towers, not just overhead satellites, which are much faster.
This is why, when you open Google Maps, you don’t have to wait a few minutes to find out where you are. Of course, this is much less accurate – especially if you want precise GPS trajectories.
Before you run or cycle, turn on your device or open the app you are using and give it a few minutes to connect to the full GPS constellation. Use this as an opportunity to stretch or warm up.
Some devices, like the one made by Garmin, will let you know if a key is good. Others, however, like the Apple Watch, won’t – you just have to cross your fingers and give them some time.
This seems like an impossible running route.
Use a Special GPS Device
Instead of using your smartphone, here are a few reasons why you might want to get a GPS watch or cycling computer:
- Battery life: Receiving GPS signals requires very little power. If you also want to use your smartphone to listen to music (or have enough power left to call someone in an emergency), it’s better to have a dedicated GPS device.
- Convenience: A GPS unit that mounts to your wrist or handlebars is easier to use than a smartphone that is stored in your bag, pocket, or armband. They also provide you with live updates on your speed and distance.
- Accuracy: While no device is 100 percent accurate, dedicated GPS devices tend to be more accurate. They can also use a prediction algorithm based on your bike speed, stride length or cadence if you lose signal.
- Better GPS chip: Specialized devices tend to use high-end GPS receivers which can pick up on dimmer signals.
If you don’t want to use a dedicated GPS device (or can’t afford one at the moment), try a few different apps and see which one gives you the best results.
I have had success with iSmoothRun and Runkeeper. Strava and the Fitbit app seem to overestimate distances.
Watch Where You Practice
The GPS signal can easily be blocked by hanging trees or the side of a steep ravine. Tall buildings can also reflect this and confuse calculations. Remember, your receiver needs to see a minimum of four satellites to position you accurately. If the view of the sky was obstructed, he would likely be in trouble.
If you need the most accurate GPS tracking possible, for example for a virtual marathon, or to determine what is best for you personally, consider your route carefully. Find a good track or open park and run there instead of dodging through alleys or down steep hills in the jungle.
Enable Secondary Satellite Constellation If Possible
GPS is not the only Global Navigation Satellite System (GNSS). There is also GLONASS (Russia), Galileo (European Union), and several others.
Some devices, such as the Apple Watch, can receive signals from these devices and will automatically connect to the strongest devices. Others, like some Garmin watches, require you to manually activate the secondary satellite constellation. Your device’s battery life will take a bit of a hit, but it might be worth it.
Use the Same Settings Every Time
Neither of the GPS settings are completely accurate, but most of them are at least consistent in how they track things.
My Apple Watch, for example, always uses the same cadence and stride length info to fill in any gaps in the GPS track. Although the overall track may come out by a percentage or two, it almost always comes out the same way.
If I switch to a Garmin watch, it will use a different algorithm to smooth my route, so it will be difficult to compare with my previous results. This is why it’s also a good idea to use the same app to log your workouts. Otherwise, you won’t know if you are actually running faster, or if the difference is simply due to the way the device or service calculates distance.
This doesn’t mean you shouldn’t upgrade your device. Instead, try to make your setup as similar as possible. Wear your watch on the same wrist and keep track of different things in the same app with the same settings. This will make your workout history much more accurate.
Accept That It Will Not Be Perfect
The GPS app is an excellent tool for tracking your training, but that’s about it. Don’t put too much stock in their results – especially the live speed updates, which are very error prone.
If you’re 10 seconds slower, you’re probably just slower. But it can also be a tracking error. Focus on enjoying your workout and treat your workout notes as a bonus.
Of course, if you really want to know how fast your 5k timings are, get down the track and run 12.5 laps with a simple stopwatch – it will tell you exactly what speed you’re holding.