I just uploaded months of running from my Garmin, including data from the Philadelphia Half Marathon. Call it a year end data dump. There I was, leopard jammies on, massive coffee in hand, excited to check out my stats from the past few races. So I looked. Then I squinted… 
What the hell?
How does that happen? How does a half marathon turn into 13.33 miles instead of 13.1? Not that huge of a discrepancy, but it’s still not the advertised-sticker for your car-stinking-13.1 miles. What’s the damn deal?!?! My marathon was 26.5. COME ON. You train all those miles, sweat gallons, lose toenails, wind up in the damn ER (Oops. That’s just me.) and your Garmin shits the bed?!?!
Don’t blame it on your Garmin.
Our friends at the Rock-n-Roll Marathon Series shared this info graphic with Tina and I and it is our duty as Responsible Running Bloggers to share this with the Blog-o-sphere. It’s a good one, in my humble opinion. Your GPS device may not read the official length of the course.
Why not?
Because GPS devices are not as precise as certified course measurement which is done by bike. (YEAY! Bikes!) It simply takes a bicycle, a “Jones Oerth” counter and a few hours of time to ride the course. That was a new word for me, Jones Oerth. I plan on using it in a sentence at least once this week. “Certified” means a course has been measured to exacting standards and is at least the stated distance. Thats the key – standardized. So take a look at this graphic. And, don’t ditch the Garmin. :-).
Read more here!
It's A Marathon AND A Sprint 
Not to mention that unless you’re in the lead pack, you’re probably dodging around people, at least in the first mile or two – every step off of the tangent adds up, especially over a half or full marathon! It’s easy to underestimate just how much lateral motion the average runner does in a given race.
The only time I raise an eyebrow is when the GPS reading comes in substantially *lower* than the reported distance. I ran a 5k two years ago where enough people’s GPSs read substantially lower, that they went back and re-measured and found that someone had misplaced the turnaround, cutting .2 mi off of the course. I’d always rather run farther than the reported distance than less!
Totally true!!! I’d definitely be bummed if it came in under. I know a few people who have had that problem. I’m over usually. And I just attributed it to dashing behind trees to pee. I didn’t know exactly how it’s measured- including some GPS limitations. Thanks for the comment! Run swiftly! 🙂
I know things like running around people, running around water stops, zig-zagging, running at the outer edge of turns, etc can add to the mileage. I ran a 12K (7.46 mi) in December and my Garmin showed a little over 8 when I was done (ha! at 4 miles my Garmin already showed 4.4). But, I blame it on the race – it is more of a fun run environment and I paid less attention of my running…maybe I didn’t take it as serious as a half marathon.
I am really bad about wearing my Garmin while training. Serious runner I am not. 🙂 I am however always surprised when I finally have the damn thing on and I run a race and it’s really off. Now I know! I love a fun race! The 50k I ran was 32.5. Not 31. But at that point, who cared!
Cool info graphic! I’m surprised they didn’t mention that some of the discrepancy is because most runners don’t run the tangents well and actually do run further than the official distance. When they measure the course, it’s at the shortest distance possible to ensure that runners, at minimum, get the advertised distance. I just have started assuming that I’ll do the tangents poorly and tack on some distance to my GPS.
Cool, right?!? I honestly had no idea how they measured and certified it. It was all news to me! Usually my races are a damn blur anyways! 🙂
Me too! I’m always impressed with people who can write detailed race reports. Mist of what’s in my head is: can I hold this pace? How many minutes until this mile is done?
It’s all a blur. A hazy, pain filled blur. 🙂
Second time commenter, second name this time my screen name. Anyway, it’s all about the tangents. The official measurer takes the straight lines, the runner has to run part of the curves. Run around people to pass them? That adds distance too. Zig zag your way to and from the hydration system? You get the picture. But just think, it makes your total mileage for the year higher! 🙂 And not just because you missed a turn twice like I did at the Delaware Trail Marathon (http://www.udel.edu/johnmack/traildawgs/tc/) in 2011!
Agreed! Hang on. You missed the turn TWICE?!?! Oh I am reading that link. I almost missed a turn at the VT50 that would have made my 50k MORE of a nightmare. I ditched the Garmin for that one. Said screw it. And stopped when I was done. (Which was apparently 32.5 miles. Someone measured wrong. 😉 )
Oh! And thanks for stopping by! Stop often! Now to read your link….
That looks like a great race! I might smell a road trip….
Yup, on a double loop course, I missed a turn twice. Only me. That is a great race though. And not overly expensive accommodations in Newark or just over the border in Elkton, MD either.
It’s on my radar! Oof. That’s a doozy.
I ran the half in Philly back in November, too, and there was no way to run the tangents. Pretty much the whole race I was having to move left or right to pass people. It was because of that some that I didn’t wear a GPS there, the only time last year I didn’t use it.
Totally true. I couldn’t have run them if I tried. It was bob and weave the whole way. I kinda felt like Rocky. 🙂
Cool! I didn’t realize that was what they used to measure courses. It is pretty much expected that in the woods the Garmin is useless… always off in one way or another. Plus I’m pretty sure that all trail races are measured by mountain goats and tree fairies, who knows how accurate those little bastards are.
They can’t count for shit. 🙂
The Delaware Trail Marathon also includes two hills in White Clay Creek State Park, a.k.a. the only two hills in the entire state of Delaware. And I forgot to mention the opportunity to go off trail for about 50 yards, probably less if I remember correctly, and go past a border sign and step in to PA and then back into DE. Different spot than the turn I missed, but stepping into PA provided me with a couple seconds of oddball comic relief.
Fortunately I never bothered to care – I just kept going till I hit the finish and called it good. In fact, I rather leave all of the distance computers where I can’t see them… If I’m looking to see how far we’ve gone I’m usually in deep trouble. 😎 nice post.
Thank you! I usually don’t run with it on. Partly because I forget to charge the damn thing. I kinda like running (and riding!) FREE!!! Liberating! 🙂
Whenever people tell me that the “race course is off” I want to be like, um did you run the tangents with a steel tape? If not, then SHUT YOUR FACE AND GET BETTER. I usually run a little bit longer on my long runs to cover any differences in my Garmin. Because it lies.
It sure does lie. Filthy animal. 🙂
I always assume there’s going to be a little bit of a difference between what the course length is and what my Garmin says. Nothing is THAT perfect. What I’m confused about is that I use my Garmin and MapMyRun on my phone when I run, and MMR is always longer than what my Garmin says. Now how do you explain that one?!
Lils, I got nothin’ for ya. I’d average ’em both. Take the mean. It’s all good. At least we’re running right? 🙂
I have always assumed it is because I still don’t really know how to use my garmin. And I’m usually right.
That makes two of us. I don’t know what I’m doing. Ever. That’s why we’re BFFs. 🙂
One of the many reasons!!! 🙂
Hmmmmm very interesting! Nice research Colby 🙂
I can’t take credit for this info graphic. Even though it’s AWESOME! I’m giggling because I am a Research Scientist in the Non-Blog world. However, in running, I’m semi-clueless. 😉
I think I would die of shock if my GPS read 13.1 for a half or 26.2 exactly for a full marathon. It’s just impossible to run the tangents unless you’re in the lead. I don’t think it’s that big of a deal – just be prepared to run a little longer in a race. Kinda interesting to learn how they measure to get certified.
I’m with ya. Seeing as how I’m Garmin-less most of the time, it doesn’t keep me up at night. I know it’s a topic of discussion which is why I dig the info graphic. Who knew? 😊 Definitely not me!
This is really freaking cool and just answered every question I ever had about this subject. Although now I wish I had a 26.21876 sticker on the back of my car.
Right?!?! Tell the truth! 🙂
Beyond crossing the aforementioned finish line, WHO GIVES A FRIG?!? I JUST RAN MY ASS OFF AND DAMMIT I CROSSED THE FINISH LINE! NOW GIVE ME MY DAMN MEDAL AND SOME ICE CREAM!!!
…AND AN ICE COLD BEER!!!!!
This is exactly why I ALWAYS try to take the “inside lane” on race courses – I try to hug the curves. Of course it’s nearly impossible to do so the entire course (dang annoying other racers). But there ya go.
So you’re a “Responsible Running Blogger”, eh? Are you just as responsible in other areas of life?
Hardly. Barely responsible. But I did find the graphic pretty neat. 🙂
Of course you try to hug the curves. You minx.
This is interesting! I was recently fighting with my brother about which is more accurate my garmin or runkeeper on his phone. This information is also good to know!
I thought it was too! I’m glad you liked it!! 🙂