Monday, 23 May 2011

Is the Great Ocean Road marathon distance correct?

As all runners have engraved in their minds a marathon distance is 42.2km or 26.2 miles. The Great Ocean Road 'marathon' is actually a 45km race, which I think might technically make me an ultra marathon runner!

The race organisers give you two official race times. One for a 'true' marathon (42.2km) and a second for the total course (45km). I mentioned in my race notes that I was surprised to see the marathon finishing line one kilometer earlier than I was expecting it to be based on my GPS watch. I'm a bit suspicious of 'official' distances after the widely exaggerated mini triathlon I took part in back in April.

I've done some internet searches on the topic, but they have all drawn a blank so I have tried to break down the arguments for and against.

Don't be silly, of course it's correct. Be happy with your time!
The arguments for it being correct:
- It is an international event, they have a responsibility to get the distance correct.
- My GPS watch is advertised as having a +/- 5% tolerance. Being 1km off is well within that tolerance.
- All of the elevation changes on the run could easily have messed up the distance calculations on the watch.

No way, too many things just don't stack up!
The arguments for the distance being incorrect:
- It might be a well known race, but it isn't (as far as I can tell) an accredited marathon. Therefore they can do what they like with the distance.

- If the marathon split distance is too short, then you have to run longer than an additional 2.8km to get to the finish. This would inflate your average pace over the final section of the race, as you'd have the time it took to run 3.8km divided by a distance of 2.8km. (I also measured the overall course at half a kilometer less than 45km which would make the results even easier to manipulate.)

I mentioned that I had a stitch at the end of the race and knew that I had slowed down. Therefore I decided to take a look at the data for the top three finishers. The official results have all of their average times dropping by 40 seconds per kilometer in the final segment of the race. Dropping from around 3min 20sec per kilometer to 4min per kilometer. The top three were still jostling for the lead until late in the race and the course record was broken. I refuse to believe elite athletes would have slowed down like this.

- I've found data for 16 other GPS watches that recorded the marathon on the day. Like mine they all recorded the total overall distance as 44.5km, not 45km. The watches that took 'marathon' timings did so at 41.2km.


All of this might seem a bit mundane. However, if like me, you are training for another marathon and would like to beat your personal best, it's important to know what your benchmark time actually is. Otherwise you could aim for something that is totally unrealistic and collapse in a heap.

If you can think of any other checks I can do, or also ran the marathon and have your own suspicions I'd love to receive your comments. Ditto if you think I'm mad and the official distance was spot on.

4 comments:

  1. I was thinking about this on my last run.

    It's quite hard to measure how far an individual runs over a marathon course for two reasons:

    1) Obviously there will be slight variations in the route each runner takes. Swaying from side to side might add up to quite a few metres over such a long course. Is the official one based on the middle of the road, for example?

    2) I am dubious about the GPS watches, because when you look at the maps they generate they are in very straight sections. I suspect they only "sample" where you are every so often rather than continuously (this would have to be the case because otherwise the battery would run down after about twenty minutes). I therefore doubt the accuracy.

    I think the watches are good for training and race planning, because they allow you to compare like with like, but I suspect that if you had to pop over to Paris to measure what they say against the official air-locked iron bar metre they have then there might be a slight difference.

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  2. 1) This is a really good point. On a twisty course the effect of meandering is likely to be exaggerated. The GOR road is two lanes and we were asked to stay in the left hand land which I did without any meandering. This could be part of the explanation as to why the marathon marker appeared sooner than I expected.

    However, the last three / four kilometres were dea straight which should reduce this effect. There is still an unaswered question on why these kms were so much slower on the official timing to me.

    2) There is a fantastically geeky site called http://www.dcrainmaker.com/ which has a lot of GPS watch reviews. I read on there that the Garmin watches take a reading every four seconds (on the more advanced watches you can change this). Therefore there will be a bit of straightlining. However, I've never noticed it as badly as you have on the maps. Indeed I'm impressed that it picks up little deviations and back tracks I sometimes do.

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  3. I know it's a late reply but only just stumbled on this now searching the same subject after this years run. I agree the distances are off. My run measured to within 30m of yours for total distance yet by my GPS the marathon marker was at 42.7 km. I consciously straight lined as much of the course as I could too. I understand the physics of GPS but can't see how our overall distance would be so similar, yet the marathon distance so different. If you look at marathon distance for both our GPS tracks they indicate the same spot suggesting they measured short for yours and long for mine. I think you just have to accept that the course hasn't been surveyed as accurately as some. Nevertheless it is a great run and you are correct that we are ultra marathon runners.
    http://connect.garmin.com/activity/501630900

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    Replies
    1. Pleased to know that there is another runner out there who as done the course that agrees with me! :)

      A great time!

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