So much so, many people are asking, are GPS running watches accurate? The GPS watch records the runner’s position several times per minute. To record this position, the watch needs to receive a signal from 3 different satellites.
The signals can be disturbed in the city with the buildings, in the forest or with the weather for example. This is the first source of possible error.
The second source of error comes from signal processing for calculating distance and speed. Each watch model has its own internal software and its own settings, which are often customizable.
In a straight line, the GPS watch is very precise while turns, especially on the track, are less well managed. This is why the instantaneous speed is rarely reliable and that an average of about ten seconds is often more accurate. On average, the accuracy is of the order of 1% or 10 meters per kilometer, or 2 or 3 seconds per kilometer. On a marathon, you should expect to see a difference of 0.5km over the 42.195km course.
In practice, set your GPS watch to have a point per second (except when you make an output of more than 6 hours because the battery discharges faster).
Real-time speed is not always a good indicator because it is based on the measurement of the last few points (last five seconds or so). It is often more accurate to watch the average speed on a lap.
I’ve written a complete hands-on review of the best cheap GPS watches for runners, where I outlined durability issues.
How does the GPS watch collect data?
I will not go into the very technical detail of why the GPS does not give 100% reliable results but roughly we can summarize it as follows:
Your watch communicates with 3 GPS satellites to triangulate your position
She takes points at very regular intervals GPS track is simply connecting all these points together
All speed data is taken from this GPS track. Depending on the conditions it is estimated that the margin of error in this GPS measurement is about 1 to 3%.
Differences due to the accuracy of GPS watch data
It sounds small like that but it represents a gap of 100 to 300m over a 10km, 200 to 600m on a half marathon or 400 to 1200m on a marathon! It is therefore normal to have discrepancies between the distance of our watches and the official distance of the competitions, which is usually measured in an old-fashioned way, in an ultra-precise way for labeled races. Many races are labeled to validate official records so if your race is so you can be sure that the distance is good. (Except error obviously but it does not represent the majority of cases!)
How to check the accuracy of a GPS watch?
Just look at the GPS track that is in your watch software. Observe the route and you will see that it is rarely the meter you did! (Apart from running in the field and in a straight line on a good day, these are not the conditions for most of our training or competitions!)
And even in a straight line, if you run in the city with buildings, power lines, antennas, tunnels or just trees … the potential disturbances are many … In fact, as soon as the connection between your watch and the GPS satellites is disturbed, the accuracy of the data that comes out is too.
Ok, you understand the idea! If I take a concrete example according to my watch, I did 42.68km during a marathon and even 43,02km during another marathon. It is 500 and 800m apart. In the end we could say that there is nothing alarming, it is in the data accuracy standards of a GPS watch! But for us rider, it has a real impact on our race management!
You also have a role in the accuracy of the data!
And then, do not forget your role in all this … As soon as you move away from the official measure of the course you do more mileage … In the end, it counts! This is important info to remember from this article, always try to take turns inside and not outside if you want to avoid doing more!
The accuracy of GPS watch data in the training
Take the margin of error into account according to its course
Moreover, when I train outside a track I tend to put a margin of 3/4 seconds per kilometer compared to what the watch gives me as info! It also depends on how far I go. It’s easy to look at the GPS track and see if it’s clean or not for a particular course. On my known routes, I know where are the risks of error. Otherwise, I take this margin “standard” as a precaution.
The accuracy of the data of a GPS watch in competition
And here comes my advice for your competitions. Listen carefully because I see a lot of mistakes of this type during races … even at my level with riders supposed to be experienced! The same principle as earlier, the GPS watch is good but it gives only an idea of the pace, do not base all your race on it! Just make the point when you go to the milestones according to your time!
Do not bet everything on your GPS watch!
The accuracy of the data of a GPS watch is far from perfect … But the GPS watch is a great tool to train! Just be careful when using it! I hope this helps you to better understand how a GPS watch works and how to use it better. If you have questions or comments, do not hesitate to ask them just below! And if you are looking for what GPS watch buy … I recommend this page that includes the best cheap GPS watches for runners.
Are GPS running watches accurate? – GPS vs Smartphone
There are currently 2 ways to record the GPS signal during a workout: a GPS watch or your smartphone on which you have downloaded a GPS application such as RunKeeper.
But what is the best choice? The most accurate?
The first thing I noticed was that this reader ran into town (in Paris). So obviously, there is everything you need in the environment to disrupt the reception of the signal: buildings, tight turns, and so on. The bridges are also very disruptive because the signal must bounce everywhere.
The palliative solution is to erase the obviously aberrant points one by one, to have a route that is close to the race route. But hey, it’s long and if you have to do it after each race, it’s long and boring.
A source of smartphone error is that they use either the GPS signal or the signal from a nearby network antenna. GPS is more accurate for localization. But when the GPS signal is weak, your smartphone hangs up at the nearest antenna. So, if you run in town, it jumps constantly from one to the other, which creates mistakes.
In addition to precision, one must also look at accuracy. Because if your smartphone tells you that you ran 10km200 instead of 10km it’s one thing. An error of 200m is not huge. But what is annoying is if next time it announces 9km700 on the same route. Then your statistics are no longer comparable because the errors are random.
Is a GPS watch more accurate than a smartphone with an application like RunKeeper?
I think it depends on smartphones (as it depends on GPS watches).
As it does not jump from one signal to another, you will have fewer outliers with a GPS watch. If she loses the signal, she will draw a straight line with the next point she can pick up (so you should not walk on the water).
Now, the GPS accuracy of the latest smartphone is still very good (see the article on the comparison of the accuracy of GPS cardio watches in which 2 smartphones were also tested).
The old smartphones could give you the impression of being drunk during your jogging, this is no longer the case with the last ones.
So, watch GPS or smartphone?
My choice would be towards a GPS watch for 3 reasons.
The first is that for an identical budget, a GPS watch will be more accurate than a smartphone. In a sense, we would expect a smartphone 700 euros is more accurate than a GPS watch 100 euros.
The second is that it’s still a lot more comfortable to have a wristwatch rather than a phone in an armband that tends to slide down your arm.
Finally, if you run in town with a GPS watch, you have the opportunity to buy a Foot Pod that will add an accelerometer synchronized with your GPS watch and improve accuracy.
What if you still want to use a smartphone and app?
Try to disable the Wifi and the phone network reception. By doing this, you force your smartphone to use only the GPS signal.
Then choose a route as straight as possible avoiding passing on bridges.
So, are you going to drop your smartphone?