Throw your GPS away when racing!

This post is inspired by a great conversation with one of my runners after we discussed his past couple marathons (including Boston – well done Rob).

There have been a number of blog posts on the accuracy of GPS units (here, cool one here, good one here too, very good one here…). If you read all the fine print that came with yours (regardless of maker) they also make it clear there is a margin of error.

I’m not going to rehash what these very good articles have already beautifully articulated. Instead I want to address GPS units and address the use, reliance and non-use of them. Rob noted that at the end of his marathons his GPS unit was reading 26.5 or 26.6 miles. As stated in the articles, certified courses follow an 87 page manual on measuring requirements and are measured multiple times with all tangents in the course considered, etc. The courses were not 26.5 – 26.6 miles long. They were 26.2 miles.

The practical implication is that on race courses you cannot rely on your GPS unit to “pace you” to your new PR. Your GPS unit thinks you’ve gone further than you really have and therefore the displayed pace will show faster times than your real physical pace. Rob’s indicated he was on 8:01/mile pace at 35K while his official split yields a 8:06/mile pace.

Though you may not think this is much let’s look closer. So, you want to qualify for Boston and your target time is 3:30:59. 8:01 pace yields a 3:30:11 and a 8:06 pace yields a 3:32:23. Up until this year (2011) with the new standards going into place (eliminating the 59 seconds), this meant that your GPS unit had you qualifying for Boston with 48 seconds to spare when in reality you missed qualifying by 1:24!

Far fetched? Not so. Rob a consummate pacer used his GPS in a marathon last year. Late in the race he calculated that he was well under his qualifying time and running comfortably. Then time continued to tick away but there was no finish line.  The buffer his GPS lulled him into believing he had was nonexistent. Panic started to set in as the finish line appeared in the distance – more than a quarter mile BEYOND his GPS marathon mark! He did qualify… be the skin of his teeth! At the time he swore that the course was long like so many other GPS wearers.

The message to all runners is clear.

GPS units are good for a general gauge of pace and distance. It (like a regular watch) is accurate on the amount of time you are out there. Certified courses are accurate. Individual mile markers may or may not be accurate depending on how the race organizer set them. No not all courses have gone through the certification process and so your local 5K may not be as accurate and in fact your GPS may be more accurate (no way to know for sure).

Use your GPS units for training. But I advise that you modify your pacing by about 1%. If your goal pace is 8:00/mile you should look for about 7:55/mile on your GPS. You are not really running faster. You are merely correcting for the margin of error in your GPS.

And finally my advice is to not become so reliant on a GPS unit in races. Stop trying to match your GPS pace every instant. Instead – use a watch (or at least pay attention only to the timing function of the GPS). And focus on getting to the finish line as fast as possible.


About Dean Hebert

I’m a mental game coach, author and speaker. I work with individual athletes, parents, coaches, and teams on sports performance enhancement. Beyond my academic post-graduate work in sports psychology - the psychology behind athlete performance – I am a certified Mental Games Coaching Professional (MGCP) and certified hypnotherapist. I’ve authored several books and hundreds of articles. “Coach, I didn’t run because…” (2008) is a seriously light-hearted look at making excuses not to workout and how to overcome them. “Focus for Fitness” (2009) and “Screw the Goals Give me the Donut” (2010) are two of my eBooks on mental game approaches for the everyday athlete. I wrote these because I believe that everyone can benefit from the powerful mental techniques that the world’s best athletes use. I have been cited in Runners World, Best Health magazine (CN), SWEAT Magazine, and the Washington Examiner amongst many other publications. I have been a featured mental games coach in Runner’s World and for the internationally acclaimed trail running resource - I also regularly appear on sports and fitness talk shows such as LTKFitness, Runnersroundtable and for more than three years I have co-hosted a weekly video series with Coach Joe English for I specialize in mental toughness training. My clients include tennis, synchronized swimming, golf, race-kart, soccer, motocross, volleyball, MMA, cycling (road, off-road, time-trialist), running, duathlon and triathlon, basketball, football and baseball athletes. I have coached world-class athletes and athletes internationally. I have a passion for working with youth athletes and helping them apply mental game skills and techniques to all areas of life. Most importantly, my aim is to have people enjoy sports and life to their fullest through peak performances.
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7 Responses to Throw your GPS away when racing!

  1. John M says:

    My GPS watch generally measures the distance on longer races at about 1% over the ‘correct’ distance, and is reasonably consistent in this. (There are technical reasons for this which I could go into, but even I find them abstruse and dull, and I’m a geek and write software for this stuff!). I always simply build in this 1% to my pace calculation, as you suggest, and it works pretty well.

    While I wouldn’t advocate slavish dependency on a GPS device, I have to say that keeping an eye on the overall average pace from time to time throughout races has been really helpful to me in achieving target times. Where it is most helpful is in stopping me from going out too fast – it’s all too easy to get caught up in the initial surge in a race, and feel like you’re going at an ‘easy’ pace, when you’re in fact going 10-15 seconds per mile faster than you can realistically sustain for the distance. My GPS watch brings me back to reality, which helps!

  2. Aric Keith says:

    I find my GPS has the opposite problem. It routinely measures short, thus making my pace appear slower than it actually is. That’s why when I need pace markers I always rely on well marked trails or tracks, or carefully map a route ahead of time.
    I’m always surprised by the number of people who think the GPS is accurate without even questioning. They run 3.1 miles out and register only 2.8 on the exact same route returning and feel they must run the last .1 to get to 6 miles!

    • John M says:

      What is your GPS device? I had a Garmin Forerunner 101 for a while, which I was not impressed with, as it seemed to lose GPS signal under even the thinnest of tree cover. Ones based on the more sensitive SirfStar III chipset, such as the Forerunner 205/305 and later, were much better (my own is in fact a GlobalSat GH615).

      • Dean Hebert says:

        Mine is a Garmin Forerunner 305. Runners in my club have many other versions. And as you can see in the technical articles it doesn’t matter – all are inaccurate to varying degrees.

  3. John M says:

    Dean, my question was actually to Aric Keith, whose GPS watch measures short, which I found to be a defect of the earlier Garmins. The 305 is much more sensitive and doesn’t suffer from this problem (which is due to lost signal).

    • Aric Keith says:

      It is a Garmin 110, the new model. Occasionally it measures long, but rarely. Sometimes it measures perfectly. But, the point is, like all GPS devices it can’t be relied upon as an accurate source of information for pacing.

  4. Pingback: Long Run – 14 Miles — Rob Run

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