Marathon Splits using yer Garmnin'

Hi, All.

 A few weeks back someone posted a really useful thread (from a couple of years back I seem to recall), about the best way of accurately keeping track of your marathon splits by manually pressing 'lap' on your Garmin at each mile marker instead of relying on Autolap.

Can I find that thread now . . . . . . .

Please can somebody point me in the right direction . . . . thanks.

Hope everyone's as fit and well as possible and looking forward to Sunday as much as me. Good luck all!


  • Press the lap button as you go through each marker? And then turn auto-lap off?
  • Hi, 1e-runner.

     Thanks for responding. I'll certainly be doing that, but the thread I saw was quite lengthy and went into quite a bit of detail. Does anyone out there know where I can find it?


  • Go CazGo Caz ✭✭✭
    Hi there

    I saw the thread a few weeks ago too and used it to adjust my Garmin. I tried it out in a half-marathon and it worked a treat, so will be doing the same at VLM on Sunday. I cannot find the thread to credit the original source unfortunately, but I did copy it down so here it is. Hope that helps.

    "We probably all know someone who has got to the closing stages of a race, thinking they’ve used their Garmin to pace themselves perfectly to dip under a certain time, only to find they miss out because “the course was long”, or tunnels, underpasses and the like mean their Garmin lost signal and threw the pace number out of the window.

    It doesn’t have to happen that way. Even on a course with tunnels, or with inaccurate mile markers, or even on a long course(*), you can set up your Garmin in such a way as to always know how you’re doing in the race, rather than get the nasty surprise at the end. I’ve been asked to explain on threads and fmails several times, so I thought I’d stick it here for posterity.

    On the screen you’re going to look at while racing, you need to have at least these two data fields displayed:
    a) Pace – Lap
    b) Time – Average Lap
    And you also need to switch AutoLap off. And AutoPause too, if you use that normally.

    You then need to hit the Lap button at each mile marker.

    So within each mile, you look at “Pace – Lap” to see how you’re doing just for this mile (don’t use Pace (current) for this, it changes too frequently).

    And for the race as a whole, you can see your situation by comparing “Time – Average Lap” to your goal pace.

    And that’s it. This will work for races with tunnels, skyscrapers, tight turns, inaccurate mile markers – anything. As an illustration:

    Say you’re trying to break 90min for a HM. So you need to run better than 6:52min/mile average for the 13.11 mile course.

    Without doing what I suggest above:
    If you steady pace mile one with your Garmin pace field showing 6:50m/m, but the Garmin distance at the first mile marker is 1.01m – then you’ll actually pass the mile marker in 6:54 (but the Garmin will have beeped at 6:50 with AutoLap).
    If every mile goes by like this, going by Gamin pace alone you’ll think you’ve cracked the 90min, but you’ll actually come home in around 90:50. The GPS distance will record 13.24m, and you might think the course was long (although it almost certainly wasn’t).
    That would be pretty frustrating, since you might think you’d paced it perfectly. It’s even more frustrating when the margin is closer, if the Garmin “over-read” on distance is less than the 1% above.

    If the same runner sets up the Garmin as above:
    Pass mile one, hit lap manually – they know that the first mile was 6:54, not 6:50. The field “Time – Average Lap” says 6:54m/m. They’re slower than 6:52 target pace and are aware of it. Until they speed up and this field reads better than 6:52, they’re still behind the pace.

    If you miss a mile marker, this method is not screwed up either – you just need to make a lap somewhere, even if it’s not accurate. As long as you have pressed lap X times when you pass the X mile marker, the field “Time – Average Lap” will be your average pace in the race to this point (it’s basically doing the same calculation you would do if you took total time and divided it by total race distance at that point).

    Forget about Virtual Partner; since the GPS measure of distance isn’t (sufficiently) reliable you can see why that isn’t a reliable method.

    (*) Officially measured courses are not long, even if your Garmin says it is. GPS cannot be relied upon to be accurate to better than 1-2% typically, so you can expect your marathon to measure around 26.5m by your Garmin."
  • That's the one!!!!!

    Go Caz . . . you're a star. Many thanks indeed.

  • Go CazGo Caz ✭✭✭
    No problem - and many thanks to whoever posted it originally as it's certainly helped me out. I think I got a bit misled by putting my Garmin on average overall pace during my last marathon. Strangely... very best of luck on Sunday.
  • Thanks again, Go Caz . . . and the very best to you too (assuming you're running?).


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