Strava said I ran 0.16 miles more than actual race distance?

The long and the short of it is that GPS aren't accurate. Things GPS watches don't like are buildings, trees, turns, and curves. If these things exist on a race course, then the watch will be off. Plus, some watch software algorithms (cough, Garmin, cough) are purposefully designed to overestimate a user's distance so the pace looks faster than reality. On another note, many race courses aren't terribly accurate either, so there is that.

GPS is not an accurate measurement for distances.

Strava has a whole posting about it on their website.

Please get educated.

Commodity GPS generally has around 10m of error for an individual measurement. Watches etc. take a sequence of measurements each of which has a few meters of error and stitch them together. The errors are not entirely random or additive, so thankfully your total error won’t be 10m x number of measurements, but it is hardly uncommon to see an extra 0.15 mi on a 6K route. So just don’t worry about it.

Try running 1K around a track three times and see what your watch measured for each 1K lap. You’ll almost certainly find that its three measurements are not internally consistent.

runne wrote:

Commodity GPS generally has around 10m of error for an individual measurement. Watches etc. take a sequence of measurements each of which has a few meters of error and stitch them together. The errors are not entirely random or additive, so thankfully your total error won’t be 10m x number of measurements, but it is hardly uncommon to see an extra 0.15 mi on a 6K route. So just don’t worry about it.

Try running 1K around a track three times and see what your watch measured for each 1K lap. You’ll almost certainly find that its three measurements are not internally consistent.

That's wrong.

One GPS data point is pretty accurate. The problem is that a bunch of data points create a zick zack course.

Try for fun to run on a track with strava and look at the outcome.

It will look like you are a drunken sailor.

Apple Watch?

Unless you are in the lead, you give up a lot of distance.

GPS is almost always going to show you "ran" a little further. Part of this discrepancy comes from the zig zagging and failure to perfectly run tangents, as you mentioned. But also keep in mind, even if you run the tangents perfectly (which is not possible) the GPS has its own inherent error. Every second or so, it pings your location. But it's not exact, every time. There's slight error. Sometimes it records you a few feet to the left. Next time, it might be right on. A time or two later, it may ping you as being a foot or two, to the right.

I've seen some tracings, where someone is running on a road, then suddenly it shows them 100 feet away from where they are across a lake, then a second later, back on the road. The end result is that even if you're running a perfect straight line (which you're not) it's going to record you as weaving, ever so slightly, sometimes more than slightly. If you measure that weaving line, it's always a little longer than the straight(ish) line you're running, or that recorded by the course measurer.

They try to correct for this in the software, but it's impossible to eliminate it completely. GPS will very closely estimate your time and distance. But it's still an estimate. I've found over the years, that my GPS (Garmin) always says I'm running between 2-5 seconds per mile faster than I am, depending on how many turns there are in the course (more turns = closer to 5 seconds, few turns = closer to 2 seconds). To correct for this, I simply make sure I'm pacing 2-5 seconds quicker than my goal, depending on the course.

Tldr: GPS watches aren't perfect, so always run 2-5 sec/mile faster than you think you need to, for time goal.

nope, Garmin...

ok, thanks!! this helps. I just don't get how watch says I went at 6:27/mi whereas chip says 6:44/mi. I trust chip much more I don't think I can run a sub 13 2 mile split during a race lol, the only thing is other peoples' watches seemed more accurate. maybe mine just goofed and I did poor tangents. but can you agree that there is no way I ran an extra 0.16 miles I mean that seems insane... ugh I'm losing sleep over this.

Your total time remains the same while your calculated pace from the watch is dividing that time by 3.88 miles and the official race result is dividing that time by 3.72 miles.

Take heart that this is still more accurate than the method we used before GPS which was to divide the time by 7 even if you were faster (or slower). Sometimes we tried to add up distances from topographical maps. Being off .15 isn’t bad.

but I feel there's no way I ran a 19:55 5k during that race. I don't trust my Garmin watch. I can't run a 12:4x 2 mile let alone race one which makes me suspicious.... but at the same time, did I run that fast??? I'm bummed because that means I could've gone a minute faster had I ran better tangents, but I think my watch must be off.... because I tried to stick by my teammates..

I understand, but I feel weird that it says I ran 6:27/mi vs. my bib splits 6:44/mi - am I wrong to trust my bib more?

No, trust the course. Especially if your watch is the anomaly amongst your teammates. There are all kinds of things that could make your watch inaccurate. Plus, it's cross country. Wait for track season if you want to get nitty gritty with your times.

xcrunner56 wrote:

but I feel there's no way I ran a 19:55 5k during that race. I don't trust my Garmin watch. I can't run a 12:4x 2 mile let alone race one which makes me suspicious.... but at the same time, did I run that fast??? I'm bummed because that means I could've gone a minute faster had I ran better tangents, but I think my watch must be off.... because I tried to stick by my teammates..

Remember, the watch is adding up distance as you go along. It's not as if you ran 6k and then the watch adds 0.16 miles afterwords. So, when you get to the 5K point in the race, the watch probably has you around 5K plus 0.13 miles. When the watch has you at the 5K point, you were probably around 4.8K on the course. So, in reality, you hit 19:55 at 4.8K.

My calculation, with the information you have provided, has you finishing the 6K using chip timing in 25:00. If the course is was 6K (3.72 miles) your official pace would have been 6:44. If your watch has you running 3.88 miles in 25:00, your watch pace would be 6:27.

yeah my time was 25:05. I somehow doubt I ran three miles in the 6:20s which is what my watch says. idk why I'm so hung up on this... I'm just frustrated that I could have apparently run a minute faster. I should probably trust my bib right?

xcrunner56 wrote:

nope, Garmin...

Could be a lot of things. Tangents, courses with lots of turns mess up GPS. Just do your best to hit tangents when you can without it slowing you down but other than that don’t worry about it. If you get to pre run your next course then look for big turns where you can set yourself up for a good tangent.

You need to relax about this, because you were in a RACE. In other words, while you might want a great time, at base (and especially in cross country) you are RACING OTHER PEOPLE. If you want to worry about your pace down to the second, then you need to wait until track.

In cross country, you have two problems.

1) Your GPS watch is not going to be accurate for all the reasons people have said in this thread and the other one you started. When in doubt, and especially in cross country, you need to go by what the official results say, NOT what your watch says. And this is not directed to you personally, though hopefully it'll help you relax about this race, but GPS watches appear to have made people exceedingly stupid. Everyone thinks the watches are exactly right, but they're not, and then people get all bent out of shape trying to explain away a result that doesn't match what they think it should be.

2) Now, as to the official results, you also need to take those with a grain of salt. A cross country course is highly unlikely to be as accurate as a track, and the course you ran is only accurate to within about 1% according to the organizers (i.e., your 6km could be off by 60 meters, or at least 15 seconds). So even going by your bib time, you can't read too much into it. You may be in awesome shape and have run a PR, but you won't really know unless you get on a track or an accurately-wheeled course.

Regardless, congratulations on your race.

thank you! I know I need to chill. there's a big difference between 6:27/mi and 6:44/mi so I just wish I almost didn't run with the freaking watch because then I'm like if I ran at 6:27/mi I could've moved up 100 places. 6:44/mi feels exactly right and a pace I'm actually surprised I was able to go at, so I'm just gonna let it go and go with what course says. as always, I could do a better job running tangents but there's no way I ran an additional 0.16 miles. I'd say +0.08 max.