My distance v measured distance

Every time I run a race I run further than the actual distance. Yesterday’s half marathon I did 13.19 miles. That’s a good extra 40-50 seconds which makes getting the time you want even harder.

I understand why this happens because the organisers measure the shortest possible distance but how do people deal with this when trying for a PB?

to get under 1:30 in a half marathon you need to run 6:52 a mile. It’s all very well training for this but then you have to do an extra 150 yards at the end!

i know I’m being a bit pedantic but does anyone stop their watch when they’ve run the distance? That would seem reasonable!! Or maybe these watches just aren’t all that accurate!

incidentally I got to 13.1 miles on my watch in 1:30:15 so didn’t make it anyway!!


  • The measured course distance, the distance your GPS gives you and the distance you actually ran are three different things, not two.  Assuming that you didn't run on the outside of the bends or zigzag across the road all the time, the distance you actually ran is probably closer to the course distance than your GPS.  The watches just aren't that accurate.

    In a race you're much better off using the mile (or km) markers to gauge pace - a pace band will tell you what time you should be at each marker (based on even pace). 

    In training, unless you're on a track or a measured course you've only got your GPS to go on.  Always take pace with a pinch of salt, especially current pace.  Average pace is better, but if it's measuring long your average pace will be shown as slightly quicker than it actually is.  How you deal with that is up to you, but personally I wouldn't be too worried - just being in a race will gain a few seconds per mile.

  • Thanks for the advice, so do you think it’s better just not to use GPS during a race? I found it quite off putting this time actually as it was wrong clearly - hadn’t thought of the GPS being the probl before 
    If you look at the instructions for your GPS it will probably tell you that generally they will over measure by a small distance about 2% I think.  If I run a marathon my GPS records at least 26.4, anything less and I would suspect a short course, 13.2 for a half.

    I think perhaps the manufacturers like it to over measure so we think we're running faster than we are, same with the calories burnt that's always exaggerated too.

    If I want to stick to a pace for say a half marathon, then I calculate that I will need to run 0.2 of a mile for the last part and factor that into my calculations.
  • GPS will measure long or short by varying amounts depending on the quality of the signal they're receiving and the number of satellites they're getting it from.  Chicago marathon GPS gave me almost 27 miles, and when I look at Strava it's easy to see why - every time the course gets into the built up area with lots of tall buildings the trace is all over the place.  At one point I apparently swam across the river twice during a 'mile' that it says took me just over 5 minutes - clearly nonsense.  Conversely the first mile included a tunnel and GPS measured it short.

    Best bet is to take splits manually at each marker - if you set one of the fields on the display to 'average lap time' and manually lap every mile then you'll have a true average pace per mile, and you won't need to worry that it's measured 5.2 miles (or whatever) in reaching the 5 mile marker.

  • G-DawgG-Dawg ✭✭✭
    Same happened to me in Chicago. The first mile underground blew my GPS accuracy. It actually helped. From then on I gave up on the GPS and just used the actual elapsed time and distance on the race clocks (deducting 3 mins it took to cross the start line). I was going for 7min miles, so doing my 7 times table took my mind off things. Bagged a PB, so it seemed to work OK.

    The Garmin 235 has both GPS and GLONASS technology for greater accuracy. Looking at the Strava mapping for the race, I swam down the Chicago River three times. However, it did eventually sort itself out as it reports a distance of 26.22. In fact, as it bleeped mile after mile, I worked out it was adjusting correctly but still couldn't trust it due to so many high buildings and running under the elevated railway.

    Having almost been caught out in Paris previously (26.5 with an older Garmin), I'll use the clock and course markers method from now on.
  • Thanks for the advice. I will do as you suggest next time
    i like the swimming stories!!!!
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