GPS accuracy on time trials

Look on the strava/garmin map and see how accurately the path traces what you actually ran.

interesting. usually when I map afterwards, it shows a longer distance than I actually ran.

strava user wrote:

I recently ran a 5k time trial on the roads and finished in 16:17. I just stopped when my watch told me I was at 3.1 miles, but I mapped it online after and it only came out to just over 3 miles. This was a sizable drop from my previous 16:42 PR, does this count? How can I tell how far I actually ran?

Sounds like you ran 3 miles. I would trust the Google Earth tracing over the GPS. If you really want to get down to it you can wheel the route.

strava user wrote:

I recently ran a 5k time trial on the roads and finished in 16:17. I just stopped when my watch told me I was at 3.1 miles, but I mapped it online after and it only came out to just over 3 miles. This was a sizable drop from my previous 16:42 PR, does this count? How can I tell how far I actually ran?

No it does not count. A GPS is not a reliable way to accurately measure an official distance for a race. For workouts, it is a very good estimate and plenty good enough. For official times, it is in no one good enough. In order to be a PR, you need to either run on a track or run on a certified course that was measured using the calibrated bike (jones counter) method.

It's funny because I've heard several people run PRs in official races then second guess their own PR because their watch came up .1 short. If the race gives me a chip time, I'm going to take that time...but that's just me.

On an accurately measured, USATF certified course, you have a point.

On your typical "Map My Run says so" 5K, not as much.

My Garmin 230 almost always comes up 100-300 meters short in Races. In my mind, I try to go with the pace/distance that the event tells me I ran, but it's hard when the watch says something else. Total mind game.

This.

Use a track for time trials or calibrate a bike computer over a known accurate distance and then measure your time trial distance on the course. Turn around, measure it back the other way. It'll be off by maybe a couple of meters per mile. Take the average distance between the two measurements.

I think... and someone correct me if I'm wrong... that a certified course adds a small amount to the distance on purpose. And I think that it's 1% add-on so a 5,000 meter course would actually be 5,050 meters long.

Maybe it's just *allowed* to be 1% too long. I'd have to look it up and I'm not interested in doing that. But you could. Just look up the certification process.

It's 0.1%, fisky.

"In competitions under Rules 1.1(a), (b), (c) and (f), the
uncertainty in the measurement shall not exceed 0.1% (i.e. 42m for the Marathon) and the length of
the course should have been certified in advance by an IAAF approved course measurer."

https://aims-worldrunning.org/...

The amount added - known as the Short Course Prevention Factor (SCPF) is 0.1% of the total distance = 5m for a 5k, 10m for a 10k, 21m for a half and 42 meters for a full marathon.

My favorite thing is when runners run a slow time on an accurate course, but their Garmin shows it to be slightly long, so they'll then post on Strava about how the course was wrong by 400m and say "about 50 seconds long".. nah dude you just ran slow on that day.

It counts for a big improvement. It's your training log, etc., so do whatever you want. But I would say use the track or a certified course if you don't want to be always wondering about that "PR".

Well considering you are using 3.1 rather than 3.11, you have already proven that you are willing to round down.

I would compare the tracks between GPS and whatever maps tool you use and be careful with the start/end points as well.

Sorry, no it doesn't count.* A correctly mapped race will almost always read longer than the advertised distance on your watch. Don't despair! If you can run that fast solo, add a dose of adrenaline, find yourself a flat, fast course, and you'll get a PR within 2 or 3 attempts for sure.

* During the pandemic, when there were no races, time trials counted. But now that the pandemic is over, we're back to pre-pandemic rules, which means PRs are only PRs if done at an actual race.

In doubt do it the old school way , with a road/city bike and tachometer.

You have to calibrate on wheel rotation exactly.

I did some track workouts (on a certified competition track) with a guy that would run reps until his GPS watch confirmed the distance. He wouldn't run shorter if his watch beeped early, but he would routinely run longer to ensure his workouts showed up "accurately" on Strava.

There’s a fairly prominent hybrid athlete influencer that does mile time trials on a 1600m track, starts in lane 3 or 4, and just stops when his GPS hits a mile. He ran like 5:06 in an official FAT mile race and posted that he ran 4:5something on Strava because that’s what the GPS clocked him at.

I genuinely cry every single time it comes up in my suggested feed, which is unfortunately a lot because of how the algorithm works.