General Discussion Triathlon Talk » HM distance way short. Rss Feed  
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2013-07-07 6:27 AM


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Subject: HM distance way short.
My hometown ran their 1st ever Half Marathon yesterday as part of celebrating 150 years as a town. Nice event right along the shore of Lake Michigan. I've ran this distance 4 times over the past year dropping my time from 2:12:xx to 1:56:xx. Ran it yesterday with the goal of finishing 1:52:00 (8:34 min/mile pace). Was really pushing my limits but starting slowing the last 2 miles and my GPS watch had my avg time dropping into the 8:40 min/mile mark. Decided to keep pushing it to see what my time would be and bam there was the finish line at 12.67 miles. So I get my official time of 1:49:21 (8:20min/mile). I ask others with GPS watches and they say they had the course also short by 0.3-0.4 miles.

My main question is would you treat this result as:

HM personal best is 1:49:21 or would you do the math to give an estimate of what your time would have been had it been the full length?

I ask this question, not to complain, just to see what others would do. I feel like i'm cheating if I say my HM personal best is 1:49:21, because running another 0.3 miles would have taken another 2 or 3 min.

I really like to use these times as yard sticks for my progress.

Thanks for your time, BT nation!


2013-07-07 7:11 AM
in reply to: TrBeau17

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Subject: RE: HM distance way short.

Originally posted by TrBeau17 I really like to use these times as yard sticks for my progress.

 

Because you want to use HM race times to view your progression, I'd estimate the time to see what it would have been for the full 13.1 miles.  If the other races were the full 13.1, might as well estimate this one too if you want to see how you've progressed.

2013-07-07 7:22 AM
in reply to: TrBeau17

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Subject: RE: HM distance way short.

IMHO, I count a PR if the course is USATF certified.  If not certified, well...I probably would not claim it as a PR.  But GPS watches are notoriously inaccurate over HM/M distances.  Small errors every mile can add up.  So if I ran a USATF certified course and my GPS came up short I'd call it a PR anyway.

2013-07-07 7:26 AM
in reply to: jldicarlo

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Subject: RE: HM distance way short.
Originally posted by jldicarlo

IMHO, I count a PR if the course is USATF certified.  If not certified, well...I probably would not claim it as a PR.  But GPS watches are notoriously inaccurate over HM/M distances.  Small errors every mile can add up.  So if I ran a USATF certified course and my GPS came up short I'd call it a PR anyway.




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2013-07-07 8:42 AM
in reply to: TrBeau17

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Subject: RE: HM distance way short.
I would take the result if it was 0.1 or maybe 0.2 off, but if you and all others w/ GPS that you spoke with had it 0.4 short then I would not. Sure, GPS can be inaccurate but unless there were huge trees obstructing view of the sky it's very likely you ran 12.7 miles.
2013-07-07 9:19 AM
in reply to: #4797461

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Subject: RE: HM distance way short.
I would do the math. I personally like to view my progress based on the standard distances. It's just easier to compare to peers, past performance, and such. Plus, I'd feel a little guilty saying my PR was xyz when I knew the course was measurably short


2013-07-07 10:35 AM
in reply to: Shop Cat

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Subject: RE: HM distance way short.
Take a look at the GPS map.  For my HIM, my GPS gave me 12.85 miles.  I looked at it and the course had a decent amount of corners and the data points show me cutting a lot of corners instead of staying on the trail.  I of course stayed on the trail/route and that settled me down a bit (not like that horrible run was anything close to brag about though...). Seeing how I passed these corners up to 3 times, I can see how it thinks I ran a shorter distance than I did.  I ran a FM to where my friend and I both had .4 miles over (e.g. watch showed 6.4 instead of 6 at mile marker)and it stayed that way the entire time.  That screwed up my pace a little bit but in that case, I'm thinking the course was actually longer than expected since the error was so early.
2013-07-07 11:42 AM
in reply to: #4797534

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Subject: RE: HM distance way short.
Interesting article that talks about this.
www.nytimes.com/2011/12/20/health/nutrition/gps-watches-may-not-track-runs-accurately.html?pagewanted=all&_r=0

I think they are still good training tools realizing their inherrent limitations.
2013-07-07 11:42 AM
in reply to: #4797534

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Subject: RE: HM distance way short.
Interesting article that talks about this.
www.nytimes.com/2011/12/20/health/nutrition/gps-watches-may-not-track-runs-accurately.html?pagewanted=all&_r=0

I think they are still good training tools realizing their inherrent limitations.
2013-07-07 2:58 PM
in reply to: TrBeau17

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Subject: RE: HM distance way short.

It's fairly common for race course distances to be off.  You could email the RD and ask how the course was measured.  A certified course will have it measured by a calibrated bicycle wheel (actually, I think 2) that cuts all the corners as close as possible and takes all the diagonals.  

If there wasn't a lot of tree cover or tall buildings messing up your GPS signal, a garmin will be within 1-2%, often better depending on how sharp the corners are.  It certainly 'could' be off by 0.4mi and perhaps you're faster than you think.  I've surprised myself on race day many times.

Then again, I've had an RD tell me that his HM course (as part of a 70.3) was measured and right on, and every person's garmin came up 1.2 to 1.3 miles long (as did my time).  

Almost no way to know...  Sounds like you ran a fast race.  Congrats.

2013-07-07 9:09 PM
in reply to: morey000

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Subject: RE: HM distance way short.
Ditch the Garmin, run with one of these.

http://www.toolbarn.com/calculated-ci6425.html

You could also be asking yourself: "How relaxed and fluid did that race feel?"

One way or another, great race.


2013-07-08 10:16 AM
in reply to: TrBeau17

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Subject: RE: HM distance way short.
I had almost the exact same situation last year (though with slower times) - the HM course came up about a half mile short on my Garmin, and it was technically a PR by two minutes, but in terms of pace per mile it came out pretty much the same as my previous PR. This course was not USATF certified, and honestly I think they measured the course using MapMyRun and then messed up the location of the start line. Queries (not just from me) on their Facebook page were brushed off and ultimately deleted. I just called it a PR with an asterisk, then went out and destroyed the PR six months later.
2013-07-08 1:59 PM
in reply to: TrBeau17

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2013-07-08 2:06 PM
in reply to: tkos


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Subject: RE: HM distance way short.
Originally posted by tkos

Download your GPS data. It will have the correct distance you ran and the p[ace you ran it at. That is the most useful data. Now when it comes to chatting about your race with people, just round it off. Call it 1:50 and have a great day.


that isn't entirely accurate - there are a lot of factors that play into the accuracy of your GPS data - how many satellites is uses to triangulate - 3 are good, 4 is better; is it also using a fixed point (like an antenna) - also known as dGPS which is even more accurate - you can't just say that your GPS is accurate - the link to the NY Times article above has some good data and experiment information on different types of GPS devices/downloads and how they calculate
2013-07-08 2:13 PM
in reply to: TrBeau17

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Subject: RE: HM distance way short.
What was the race called?
If it had a decently large field, then you will be able to search on Garmin connect and see how other's measured it.
In response to the NYT article, please read this: http://www.dcrainmaker.com/2011/12/why-new-york-times-gps-running-a...
2013-07-08 2:36 PM
in reply to: dfroelich


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Subject: RE: HM distance way short.
Very small race (under 300 runners), 1st time they ever organized such an event. Called the Delta Heritage Half Marathon. Starts in Gladstone, MI and runs to Escanaba, MI.


2013-07-08 2:46 PM
in reply to: TrBeau17

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Subject: RE: HM distance way short.
Looks like someone else got a very close distance to yours: http://connect.garmin.com/activity/339186008
That was the only one I could find. I would be more inclined to believe a course is GPS measured short rather than long since there are more common errors leading to a longer GPS track than short.
Factors leading to a long GPS track: not running the tangents and GPS tracking errors leading to zig-zag rather than straight lines
Factors leading to a short GPS track: losing GPS reception leading to a straight path (that could be curvy).
Those are the big ones. If you control for those 3 things, you may get within the .5-1% accuracy that the watch makers claim, but more likely watches read longer than the actual path. If they read quite short and there are clear skies...then it was likely a short course.
2013-07-08 4:49 PM
in reply to: dfroelich


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Subject: RE: HM distance way short.
12.64 miles is what that link said. Mine said 12.67.
2013-07-08 6:56 PM
in reply to: #4797603

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Subject: RE: HM distance way short.
use Google earth to retrace the route. That will be accurate. My GPS is always a little off
2013-07-08 7:40 PM
in reply to: TrBeau17

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Subject: RE: HM distance way short.
Originally posted by TrBeau17

12.64 miles is what that link said. Mine said 12.67.


0.03 miles off on a 12.655mile (average) run is only 0.023%error. That is pretty darn close!
Now...if you had 10-12 people all within the 12.5-12.7 range, then I would feel quite confident that you all ran a short course. Because: A) there are no tunnels or dense tree coverage and B) the usual suspects of GPS error are randomly long or short.

I will disagree that drawing a line on google earth makes a better distance approximation than GPS.In my experience, drawing a line is within 10% and GPS is within 5%. (Especially since we have 2 GPS tracks that are so closely in agreement!)
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