Technology vs race distances??
Discussion
I'm pondering which of the two is more accurate, specifically in my case my Garmin Forerunner vs race distances.
I have noticed on the last 2 events I have done that my Garmin disagrees with the run distance.
I know in areas that are heavily covered the Garmin can be a bit inaccurate as there is one race I regularly do in a forest that the organisers insist is 5k yet all the sports watches are registering about 4.4k.
But in open areas like today the trace from the garmin exactly matches up with the route on the satellite image.
Today I did a 10K and my garmin registered it at 6.3 miles not 6.2 so roughly 160m difference. I ran a PB today according to the chip timing but if I went with my Garmin there would be another 28sec off it.
Similarly I did a Parkrun last week and again did a PB there of 19.00 which is supposed to be 5k. My Garmin and strava disagreed and said my 5k time was 18.52
So which one should I go with to track my 5k and 10k PBs?
I have noticed on the last 2 events I have done that my Garmin disagrees with the run distance.
I know in areas that are heavily covered the Garmin can be a bit inaccurate as there is one race I regularly do in a forest that the organisers insist is 5k yet all the sports watches are registering about 4.4k.
But in open areas like today the trace from the garmin exactly matches up with the route on the satellite image.
Today I did a 10K and my garmin registered it at 6.3 miles not 6.2 so roughly 160m difference. I ran a PB today according to the chip timing but if I went with my Garmin there would be another 28sec off it.
Similarly I did a Parkrun last week and again did a PB there of 19.00 which is supposed to be 5k. My Garmin and strava disagreed and said my 5k time was 18.52
So which one should I go with to track my 5k and 10k PBs?
Always chip time, or gun time for record purposes. Doesn't matter what you recorded for yourself - it's what the official time gives you that matters. In rare cases, the runner's own measurement is correct (see below).
GPS doesn't like tree cover/tunnels, thick cloud cover, switchbacks or sharp turns.
Also, a lot of people don't actually run a clean line during a race due to either not realising, or the course being too congested etc. To illustrate how easy it is to add needless distance to your race, running a lap of the track in lane 2 versus lane 1 will add around 7m extra to the 400m standard measurement.
Finally, officially measured races with certificates include an error compensation factor into the distance. I forget what it is exactly, but it's to ensure the race isn't short for the purposes of records etc. This sadly fell apart in the case of the Manchester Marathon and a bunch of other races in that neck of the woods; the course measurer's measurement wheel wasn't calibrated correctly to result in short races, but wasn't picked up until earlier this year.
GPS doesn't like tree cover/tunnels, thick cloud cover, switchbacks or sharp turns.
Also, a lot of people don't actually run a clean line during a race due to either not realising, or the course being too congested etc. To illustrate how easy it is to add needless distance to your race, running a lap of the track in lane 2 versus lane 1 will add around 7m extra to the 400m standard measurement.
Finally, officially measured races with certificates include an error compensation factor into the distance. I forget what it is exactly, but it's to ensure the race isn't short for the purposes of records etc. This sadly fell apart in the case of the Manchester Marathon and a bunch of other races in that neck of the woods; the course measurer's measurement wheel wasn't calibrated correctly to result in short races, but wasn't picked up until earlier this year.
Edited by Cybertronian on Sunday 4th December 18:21
This piece explains it well (to my simple mind anyway!)
https://www.theguardian.com/lifeandstyle/the-runni...
https://www.theguardian.com/lifeandstyle/the-runni...
The official time/distance, not the Garmin one.
Unless they make a cock up (as the Manchester Marathon) courses are measured along the shortest route by calibrated instruments.
Garmin's and other sat nav devices suffer from discrepancies because of several reasons.
Obviously covered/confined spaces is one, however they tend to cut corners, you might not be following the shortest route and also the trace might be straightened on screen.
I'm always amazed by how much an out and back run along the same route can vary on the Garmin. I have seen a variation of more than 0.1 miles between the outgoing and return legs on a 10 mile run (5 mile out, 5 mile back).
The Garmin etc might provide an indication if the course is way off, but on small variations I'd always trust the course measurement over the gps.
Unless they make a cock up (as the Manchester Marathon) courses are measured along the shortest route by calibrated instruments.
Garmin's and other sat nav devices suffer from discrepancies because of several reasons.
Obviously covered/confined spaces is one, however they tend to cut corners, you might not be following the shortest route and also the trace might be straightened on screen.
I'm always amazed by how much an out and back run along the same route can vary on the Garmin. I have seen a variation of more than 0.1 miles between the outgoing and return legs on a 10 mile run (5 mile out, 5 mile back).
The Garmin etc might provide an indication if the course is way off, but on small variations I'd always trust the course measurement over the gps.
Cybertronian said:
I forget what it is exactly, but it's to ensure the race isn't short for the purposes of records etc.
0.1% or 1m per kmCybertronian said:
This sadly fell apart in the case of the Manchester Marathon and a bunch of other races in that neck of the woods; the course measurer's measurement wheel wasn't calibrated correctly to result in short races, but wasn't picked up until earlier this year.
The problem was that the test distance that was used to calibrate the bike had been measured incorrectly.bigandclever said:
This piece explains it well (to my simple mind anyway!)
https://www.theguardian.com/lifeandstyle/the-runni...
That's a good article. I've done a bit of course measuring (for parkruns) so read up everything I could find on the subject, and as carefully as I could, calibrated the wheel, measured and remeasured courses.https://www.theguardian.com/lifeandstyle/the-runni...
It's really annoying, having walked it 3 or 4 times when people tell me it's not 5k 'Because my Garmin says'. I just tell them to measure it with a wheel and then come back and we'll compare their measurements with mine
Someone once did ask us to change his time because his Garmin said he'd done 5k in 19.55 but we gave him 20.02 at the point he crossed the finish like. How we laughed!
john2443 said:
Cybertronian said:
This sadly fell apart in the case of the Manchester Marathon and a bunch of other races in that neck of the woods; the course measurer's measurement wheel wasn't calibrated correctly to result in short races, but wasn't picked up until earlier this year.
The problem was that the test distance that was used to calibrate the bike had been measured incorrectly. A friend of mine that lost his London GFA entry because of the additional 2 minutes added on to his time cared not why the course measurement went wrong, only that it and so many other races had.This talk of measuring with wheels reminds me of something I have wondered before.
How accurate is a calibrated wheel/ bike on an offroad course?
Not a problem with my recent 10K but the parkrun is an uneven gravel path and most of the events I do are xcountry with very uneven ground, surely a wheel cant measure point to point distance accurately if its going up and down as well as forwards?
This is what makes me sceptical about the 5k forest race I do where the organiser insists its a wheel measured 5k but nobody gets close to it on their watches and we all seem to run 5k about a min or 2 faster than we do anywhere else. Its very uneven ground with lots of deep divots / puddles and small mounds to go up and down. I think they have managed to add in 1/3-1/2 a mile in vertical distance that as runners we dont really cover.
How accurate is a calibrated wheel/ bike on an offroad course?
Not a problem with my recent 10K but the parkrun is an uneven gravel path and most of the events I do are xcountry with very uneven ground, surely a wheel cant measure point to point distance accurately if its going up and down as well as forwards?
This is what makes me sceptical about the 5k forest race I do where the organiser insists its a wheel measured 5k but nobody gets close to it on their watches and we all seem to run 5k about a min or 2 faster than we do anywhere else. Its very uneven ground with lots of deep divots / puddles and small mounds to go up and down. I think they have managed to add in 1/3-1/2 a mile in vertical distance that as runners we dont really cover.
Fairly sure no bigger trail races use a wheel; it's multiple GPS devices (to get an 'average') and as many fixed data points as you can get.
If you're bored you can read what the ITRA (International Trail running Association have to say on it :
http://www.i-tra.org/page/299/evaluation_trail_tra...
and
http://www.i-tra.org/page/296/%C3%A9valuation_trai...
If you're bored you can read what the ITRA (International Trail running Association have to say on it :
http://www.i-tra.org/page/299/evaluation_trail_tra...
and
http://www.i-tra.org/page/296/%C3%A9valuation_trai...
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