Distance-measure gets out of sync in race

SteveCRunnerSteveCRunner ✭✭✭

Hi -

I like to use a Garmin 305 during races for pacing.(Let's take that as a given.) In other words, I set a target to complete the distance in a certain time, in effect running flat splits (On the Garmin this can be set and then seen directly using a virtual partner.) How do you compensate if your GPS or footpod measuring device indicates a different distance to the real distance run, as a race or event gradually unfolds?

Twice now I have run a marathon in which the 305 gradually showed more and more discrepancy with the km markers. By 21 km on my last mara, it was showing 21.6 km. When I woke up and realised this meant I had actually been running slower than my target, I had to speed up by 3% for the second half just to get back on target, something that proved too much on the day. Plus mental arithmetic is difficult at such times.

 I just wondered how people cope with this: do you look at every marker to check, and adjust speed accordingly? Maybe you add a bit onto the target distance before you start, to allow for any inaccuracies? I'd probably try the former next time, but would be interested in any experiences or solutions.


  • Add a bit on to the distance before the start.

    0.1 mile for a 10k, 0.15 for a half etc.

  • All I do is just work out my total pace, and just use the virtual partner, not set it to a certain distance, its worked for me.
  • Hmmm Thanks danowat, I'v e never used the pace option in Virtual Partner - if one doesn't put in a distance too, it should work, but if one puts in distance at a desired pace, then it will be prone to the same error? I'll have to check this evening.

    Thanks Richard for confirming that other possibility.

  • Mr PuffyMr Puffy ✭✭✭

    I've learned the hard way, and always use my timex watch and the distance markers while referring to the garmin for pace. TBH I use it less and less in races now, especially when the markers are in Km.

  • Just don't use the distance, there is no need to IMO, last race I did, I set my 405 to my goal pace, which was 10k in 62mins, so a virtual partner pace of 9:58, during the race, I just kept an eye on how far ahead, or behind the VP I was, and that was a good gauge of my finish time, at the last couple of K, I could see I was getting close to 2 mins ahead of the VP, so I knew I was on target for sub 60mins.

    I would just be a little worried setting the distance that it would finish the "workout" before I'd actually finished the race!!!!

  • DW on the last point - yes, I always had to keep an eye that the programmed distance didn't finish before the actual race finished, and if necessary press start again. So you've told me how to eliminate another problem, thanks image

    On the first point DW, I didn't realise the virtual partner pace did not require a distance input - I'll have to try that - part of the interface I've not experimented with. But anyway, if it thinks I have done 21.6 km, when actually I have done 21.0 km, the pace calculation and the virtual partner display will still be out, even if one doesn't need to program in a target distance.

    But your suggestion simplifies things, and I could just keep an eye on how far it thinks I am ahead/behind of reality as defined by course-markers, and make a mental allowance for what I should be seeing on the virtual partner display.

  • I do as Mr Puffy does. Timex watch and mile markers. Simple is good.
  • Yes, in theory the pace could still be a bit out, but we are talking minute amounts, and I'd rather have the pace a fraction out, than the workout finishing before the race.

    Its worked fine for me everytime, mind you, I am always pretty conservative on my goal pace, and pretty much always tend to beat it by a fair amount!.

  • Thanks for your help dw, but I think you must be missing a point slightly. It is not minute. In real life the 305 guided me at a pace that brought me to a point 600m short of 21 km instead of 21 km; whether I select pace or distance in a set time it doesn't solve the problem because both depend on accurate sensing of distance travelled. It takes me another 3:20 to run those 600 m! Expressed as pace the difference would maybe look small because I would only have needed to run 1% or so quicker to avoid this, e.g. about 5:20 instead of 5:30 / km. It probably helps to have experienced this problem to see what I mean.

     So I think I will still use the Garmin to make sure my HR is not excessive but pay attention to the stopwatch and markers next time - maybe even print one of those primitive paper pace bands from this website - thanks, people!

  • Watch and race markers. Why complicate something that quite frankly is bliddy simple?

    If need be printout the RW race pace band.

  • LS21LS21 ✭✭✭

    I use my 305 for pacing but I never use Virtual Partner in a race - I just have the 'Current Pace' as an option on one of the screens and 'Average Pace' as another option - this is enough for me to work out if I'm on track or not. I ran a Marathon on Saturday and my plan was to run the first 18-20 at 7'20 to 7'30 pace - all but 2 of those were bang on the mark, and the other 2 were a 7'14 and a 7'16. So if you know your strategy beforehand then you can use it that way.

    I take the point re normal watch and mile markers but 2 things affect that I think:

    1) the mile markers are not always correct either. In loads of races I've had a mile according to the markers measure quite a bit too long or too short. They normally always tally up ok at the end, but individual markers can be wrong a lot of the time. This could mean you end up backing off/picking up your pace when you don't need to.

    2) I like having the option of checking my pace between mile markers. This is particularly important for the early stages of a Marathon I think to stop you going off too quick. I wanted to run 7'20 miles as said above. If I went through a mile in say 6'50 I wouldn't know I'd gone too quickly until I got to the mile marker - with the Garmin I can check much more frequently, and got sorted on my pacing much easier.

    So that works for me pretty well, or at least it did on Saturday!

  • MuttleyMuttley ✭✭✭

    As the others say, watch and mile markers. In a marathon you've got 26 goes to get your pace right.

    I used my Garmin in a couple of races then gave up. Too many variables affecting the readout, and anyway it's the organizers' measurements that count. The Garmin just became a distraction.

  • I've now used my Garmin in two half maras and a 10k, and it's been extremely helpful.

    As pointed out, to find at the end of the first mile that you've run way to fast is too late (or it is for me).  By knowing my pace as I'm going along I can make sure I keep it down.

    I have a 405 and it has been spot on on the overall distances, and usually, if not always, with the mile markers.  Where it has disagreed with the markers, I've gone with the Garmin.

    I used to be less than enthusiastic about technology for running, but I'm totally converted image

  • Personally I'm all for just a stopwatch in a race (notably my 305 sometimes shuts down on me) and rely on the mile/km markers!

    I find doing the arithmatic in my head on my pace gives me something to think about other than the ache in my feet


  • You do realise that using your pacing device is classed as assistance under UKA rules, so if it's a UKA event then you are liable to disqualification?

    You can use a HRM in races over 10k, but no other technical device (eg. GPS).

  • Yes, I do realise the law is an ass on some occasions (if you are talking to me) CM, but in any case I do not race in the UK, possibly for that very reason image
  • I'll talk to anyone who'll listen, Steve!

    On the whole, I tend to agree with you.

    But I think the point needs making, so that runners (as well as legislators) are made aware of the discrepancy between the rules and common practice.  Maybe eventually it'll be opened up for debate.

  • Just how hot are the "run of the mill" events on the rules?, in every event I have been at, there have been stacks of GPS devices.
  • Not very hot at all, I think image

    Rule 21 just uses the term 'technical device' - so I wonder if an ordinary watch counts as such?

    I've seen elite runners in big money winning events checking their watches, which makes UKA look a bit silly, doesn't it?

  • TBH, at my "level" of competition (if you can even call it that!!!!) I have never even thought about rules and regs, is every event covered by those rules and regs?
  • MuttleyMuttley ✭✭✭

    Well, my experience of real-time pace readings on Garmins is that they're a bit erratic. There's a lot of calculation going on in that little unit and the readout is usually behind the time. I'm not convinced of their value for serious purposes. The other problem is that people get obsessed with their pace every few metres and spend more time peering at the GPS screen than watching where they're going (I know, I used to do that).

    As an antidote to this and to restore spatial awareness, I recommend wearing an iPod image

  • Realtime calculation is frankly pants on any GPS watch, avg pace over a mile is much more reliable.
  • Agreed, but there's a setting somewhere to set the degree of smoothing - changing it to "Most" helps.
  • Given the numbers of people using GPS in races, I don't think the organisers are bothered.

    I use it to make my run more comfortable and therefore more enjoyable - I'm never going to win anything, so it's not really an issue if I did get disqualified. 

    I'd still know what my time was, from my handy Garmin image

  • Want to run a sub X time race of a certain distance, harden up and train for that.

    600M short of 21KM, poor training.

  • No, poor gps lock is what we are talking about, and how to make allowance for it, Taffia
  • LS21LS21 ✭✭✭

    I take the point that the 'Current Pace' setting on the Garmin can be a bit erratic and lags a bit behind, but I still find it an extremely useful tool just to keep things in check really.

    If you've done plenty of training runs at your anticipated race pace then you know roughly how fast you're running just from how you feel - but a quick check on the 'Current Pace' screen just makes sure you're about right. I find this really useful in a Marathon in particular becuase it slows you down a bit, especially early on. How many people have suffered in the last 6 miles because they went off a bit quicker than they intended? If you use your Garmin sensibly you can address that - you don't need to check it every 10 yards or so - just a quick glance every few hundred yards to check is all it takes and you're sorted.

    As I say, it worked an absolute treat for me last weekend in my Marathon - my pace was perfect. I ran the first half in 1'36.22, and the second half in 1'36.02 and all I did was to check it every so often and just back it off a bit so I didn't blow up at the end.

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