Since 1982 I've written a newsletter, Running Commentary. A new issue appears here each week, and material is archived.

Thu, 04 Oct 2012 04:12:42 -0400

How Many Miles?

RUNNING COMMENTARY 957

(The latest, and probably last, home for my magazine column was Marathon & Beyond. That seven-year stay ended in 2011. Now I have permission to republish those pieces. This one comes from the July 2007 issue.)

Since the 1960s I’ve just run by time, letting the mileage and minutes-per-mile fall where they may, unchecked and unguessed. That’s fine for me. But the runners I now teach and coach won’t settle for such vague accounting.

I doubt if you will either, because the time-only plan has always been a tough sell. Like you, my students demand to know how-far, how-fast. Chances are, you think you know. Chances are even better that you’re a little to a long ways off, depending on your measurement method.

For my marathon groups and college classes I originally measured courses an old-fashioned way – with a bicycle odometer, adjusted for manufacturer’s error. This result satisfied me, but the students often questioned the accuracy of my routes.

One would say, “It’s short of 15 miles. My GPS watch puts it at 14.76.” Another would insist, “We ran longer than six miles. Map My Run lists this course as 6.23.”

These runners might be right, I might, or the most accurate figure might be something else again. Even in this age of sophisticated measurement tools, the mile remains a slippery standard, hard to pin down precisely.

Despite my time-running leanings, I stay interested in how well courses are measured. That’s because, like you, I want race distances to be as correct as possible – and because almost everyone still runs by the mile and wants to know how true these miles are.

So let’s look at the ways runners check their miles, from least to most accurate. This list also traces fairly closely the history of measurement:

– WILD-GUESS METHOD. After winning one of my early road races in “world record” 10K time, I guesstimated the true distance at 5¼ miles. The race organizer apparently hadn’t even quick-checked the course by car.

– PEDOMETER METHOD. These devices, which I tried and discarded early on, are hopeless for runners. They’re good at counting steps but not at calculating the length of those steps, which vary widely from runner to runner and for you within any run. You could guess distances as closely, which means coming within a mile in 10.

– MINUTES-TO-MILES METHOD. Here you run a unmeasured course and divide the total time by your typical pace per mile. But that pace differs from day to day, so your estimate could be off by a half-mile in either direction.

– CAR METHOD. This remains the most common way to measure courses. Its weaknesses: car odometers aren’t always accurate and aren’t calibrated closer than tenth-miles; you can’t often drive the shortest possible route that a runner would take, and you can’t drive off-road where a runner might go. Cars almost always measure courses longer than they really are.

– MAP METHOD. Using a large-scale map, we once measured with a ruler. Now this method is easier with web devices by the dozen. (Google the term “running routes” for a list.) These can be fairly accurate – if the course involves mostly straight-line running. The more curves, the lower the reliability of plotted distances.

– TRACK METHOD. If you don’t mind feeling like a caged hamster, run on a track. Standard tracks are four laps to the mile. Unless they’re 400-meter track and your laps four laps fall about 10 yards short of a mile. Or unless you run in lanes other than one, when each lane out from the curb adds several yards per lap.

– GPS METHOD. It’s the current favorite, but runners put more faith in these devices than they earn. In my marathon training group, three runners wearing the same brand and model of GPS watch can get three different distance readings. The discrepancies aren’t huge, maybe a tenth-mile over double-digit distances. But if the technology were perfect, they’d all agree to the hundredth of a mile.

– BICYCLE METHOD. This one is better than the one above, but not so good as the one below. You attach a speed-distance calculator to your bike, then calibrate that device on a route known to be precise. My odometer registers 1.04 on the dial for each true mile. I trust these readings more than those from GPS watches because my device doesn’t blank out under trees and bridges. (Walking the course with a measuring wheel, after calibration, works just as well as biking but takes much longer.)

– CERTIFICATION METHOD. The only recognized way of certifying courses to USATF standards is with a counter mounted on the bike wheel, calibrated against a short course measured to a surveyor’s degree of accuracy – to the inch. The race course is then ridden carefully, along the shortest possible route. If a course is advertised as “USATF certified,” you can trust that the miles are the closest possible to true. But you will run exactly that far only if you hug the course as measured, which isn’t possible in crowds and means you run a bit beyond full distance.

A true mile is still hard to find. You can see why I opt for by-time running. All you do here is punch on the watch at the start and off at the finish, and you know precisely what you ran – not how far but how much. You can trust today’s watches to measure true minutes.

UPDATE: Soon after writing this column, I surrendered. Instead of quoting my bike-measured distances to our groups, I began using GPS figures.


[Many books of mine, old and recent, are now available in three different formats: (1) in print from Amazon.com; (2) as e-books from Amazon.com and BarnesandNoble.com; (3) as printable and shareable PDFs from Lulu.com. The other titles: Home Runs, Joe’s Journal, Long Run Solution, Long Slow Distance, Marathon Training, Run Right Now, Run Right Now Training Log (not an e-book), and Starting Lines, plus Rich Englehart’s book about me, Slow Joe (e-book only). The middle book of the memoir series, Going Far, is being serialized in Marathon & Beyond magazine, starting with the September issue.]
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