Tracking your runs, bike rides, and other workouts is fun because you can see how much you are improving (or, in my case, not improving). To be effective, however, you need to get the most accurate GPS results possible. A 4 or 5 percent error can be the difference between an average race and a personal best.
How GPS Works
The Global Positioning System (GPS) is a very complex setup. There are 24 satellites (plus a few spare parts, at all times) orbiting approximately 12,550 miles above Earth every 11 hours and 58 minutes in one of six different orbital planes. That’s four satellites per orbit.
They are distributed so that there are always at least four satellites above, everywhere on Earth. Most often there are six or eight overheads. GPS satellites constantly transmit their exact time, orbital position, and the status of the rest of the constellation, which is the information that makes GPS work.
The ground control network is managed by the US Air Force, which coordinates everything and makes sure the GPS network remains accurate.
Then, of course, there is your receiving device. It collects signals from all the satellites it can connect to and uses the information they broadcast to calculate your location as accurately as possible. If all is well, the results will be accurate to about 30 feet.
However, not all GPS receivers are created equal. Satellite signals are not particularly strong and can be blocked by hills, tall buildings, or even trees and cloud cover. More powerful receivers, however, can pick up weaker signals and maybe even connect to more satellites.
It’s kinda crazy, this is the system I use to track my easy Saturday morning 10k around my local park.
Let your GPS lock
GPS is designed for accuracy, not speed. It may take a few minutes for a receiver to lock onto the four (or more) satellites needed to calculate an accurate position. That’s why apps like Google Maps cheat a bit.
While most smartphones have a real GPS receiver, a lot of their positioning is done by assisted GPS (at least until they get a GPS lock). It triangulates your location relative to nearby cell phone towers, rather than just overhead satellites, which is much faster.
That’s why when you open Google Maps, you don’t have to wait a few minutes to find out where you are. Of course, it’s a lot less precise, especially if you want an accurate GPS track.
Before you run or take a walk, turn on the device or open the app you’re using and give it a few minutes to connect to the full GPS constellation. Take the opportunity to expanse or warming up.
Some devices, like those made by Garmin, will notify you when they have a good lock. Others, however, like the Apple Watch, won’t: you just have to cross your fingers and give them a little time.
Use a dedicated GPS device
Instead of using your smartphone, here are a few reasons why you might want to get a GPS running watch or a bike computer:
- Battery life: Receiving GPS signals requires a lot of energy. If you also want to use your smartphone to listen to music (or have enough charge to call someone in an emergency), it’s best to have a dedicated GPS device.
- Convenience: Wrist or handlebar mounted GPS units are easier to use than a smartphone that is stowed in your bag, pocket or armband. They also give you live updates on your speed and distance.
- Precision: While no device is 100% accurate, dedicated GPS devices tend to be more so. They can also use predictive algorithms based on your bike speed, stride length, or cadence if they lose a signal.
- Best GPS Chips: Dedicated devices tend to use high-end GPS receivers capable of picking up weaker signals.
If you don’t want to use a dedicated GPS device (or if you just can’t afford one right now), try a few different apps and see which one gives you the best results.
Watch where you train
GPS signals can easily be blocked by overhanging trees or the steep sides of a gorge. High-rise buildings can also reflect them and confuse calculations. Remember that your receiver must see at least four satellites to position you accurately. If his view of the sky is blocked, he will probably have a hard time.
If you need as accurate a GPS track as possible, say for a virtual marathon, or to set a personal best, then carefully review your route. Find a nice outdoor trail or park and run there instead of dodging alleys or descending steep hills in the woods.
Activate secondary satellite constellations if possible
GPS is not the only global navigation satellite system (GNSS). There is also GLONASS (Russian), Galileo (European Union) and a few others.
Some devices, like the Apple Watch, can receive signals from these and will automatically connect to the stronger one. Other, like some Garmin watches, require you to manually activate secondary satellite constellations. Your device’s battery life will take a bit of a hit, but it’s probably worth it.
Use the same setup every time
No GPS setup is perfectly accurate, but most of them are at least consistent in the way they track things.
My Apple Watch, for example, still uses the same cadence and stride length information to fill in gaps in the GPS track. While the overall track may be exceeded by one or two percent, it will almost always be exited the same way.
If I were to switch to a Garmin watch, it would use a different algorithm to smooth my route, so it would be difficult to compare with my past results. That’s why it’s also a good idea to use the same app to record your workouts. Otherwise, you won’t know if you really ran faster or if the difference is simply due to how devices or services calculated the distance.
It doesn’t mean that you should never upgrade your device. Instead, try to keep your setup as similar as possible. Wear your watch on the same wrist and track things in the same app with the same settings. This will keep your training history much more accurate.
Accept that it won’t be perfect
GPS apps are a great tool for tracking your workout, but that’s all they are. Don’t put too much emphasis on their results, especially the live rhythm updates, which are extremely error-prone.
If you were 10 seconds slower, maybe you were just slower. But it could also be a tracking error. Focus on enjoying your workouts and treat your training record as a bonus.
Of course, if you really want to know how fast your 5k time is, head to a track and run 12.5 laps with a simple stopwatch – it’ll tell you exactly what pace you’ve held.