Tuesday, April 19, 2011

Measuring a race course

I've been helping organize the Running For Risa Benefit Marathon (Half marathon, 5K, and Kid's fun run too).  The race is this Saturday.  So last Saturday I measured the course.  (I wrote this a while back... and never posted it.  The race was April 23rd)

If you're not a runner or not interested in knowing how a course is measured... you might consider stopping here.

The original plan was the measure the course with a car's odometer.  When that was brought up at a meeting, I immediately thought that was not accurate enough.  I volunteered my Garmin GPS watch.  I thought it would be more accurate than a car's odometer.  Andrea reminded me that our Garmins were off when we ran the Newport Half Marathon last year.  It said the course was short. (Although I do think the course was short).

So I started looking into how race courses are measured.  My next thought was a bike computer had to be more accurate.  As I researched it, I found out that courses are officially measured using a simple device called a Jones Counter.

A Jones Counter is just a couple gears and an analog counter.  It mounts to a bike wheel and counts revolutions made as the wheel turns.  Being a pretty detail oriented person, I wanted to measure the course with one of these.  I wanted it to be accurate. 

Through our race sponsor Marathon Pizza, I got the name of someone who would let me borrow their Jones Counter.  An easy drive out to Clackamas and the counter was in my hand along with a map of a calibration course in Hillsboro.

Next I needed a bike.  I have a mountain bike but riding a long distance on roads with that bike wasn't appealing.  As I was picking something up from my brother-in-law, I saw a road bike in his garage.  He was nice enough to loan it to me and find his bike computer that had been calibrated to the size of the wheel.  The bike computer counts each turn of the wheel to calculate distance.  The Jones Counter counts fractions of a turn of the wheel.

Saturday Morning, with the Jones Counter mounted to the bike, I headed out to the Calibration course.  Blair Hasler volunteered to help.  Between an accountant and an engineer, we were bound to figure it out.

Normally we would have to measure a calibration course.  You have to measure a course at least 300 meters long with a steel tape with 10lbs of tension on it.  Luckily the guy that loaned me the counter told me about a certified 800 meter calibration course near the Hillsboro Airport.  There were nails put down at the beginning and end of the course.  I rode the course 5 times and wrote down the counts.  I was really surprised at how close the count numbers were.  My second and third rides had exactly the same number of counts.  On a 800 meter course I thought that was pretty good.

We used an average of those numbers to calculate how many counts equal one mile.  You have to round the number of counts per mile to a whole number.  Then we figured out the counts needed for all the points along the race course.  We added in a "safety factor" of .01.  When measuring a race you are supposed to add in .01 to prevent the course from being too short.  USATF certified courses all have this safety factor built in.  So each mile is actually 1.01 miles if you run the exact route the course measurer rode and there was no rounding or measuring error.

At Hagg Lake, we drove the proposed course with the race director.  The loop around the lake is a little over 10 miles.  The original plan was to go around the lake and then out and back on Scoggins Valley Road.  After driving up Scoggins, we started to think of alternatives.  Scoggins was gravel and steep rolling hills.  I wouldn't be able to ride the road bike on that road.

We adjusted the course so that we stayed on the paved roads and just doubled back to make up the extra 2.5 miles.  We determined the start and finish lines which we decided to make the same.  We decided to make the full marathon course exactly two laps of the half marathon course.  That made start and finish lines, course management, aid station placement, timing, number of volunteers, and distance we had to measure much easier.  It even made the course safer with no one running down a steep small gravel road to no where.

I started out exactly positioned on the start line and rode the "shortest possible route."  Blair drove behind me with stakes to stake out the mile markers.  I had the bike computer and my GPS watch also ready so I could compare.  As I got to where we thought mile 1 would be, something was wrong.  The bike computer said I had gone about .63 miles.  I parked the bike and walked over to the car to talk to Blair.  We looked over the calculations.  We had used the 1 Kilometer number (we calculated for measuring the 5K) instead of the 1 mile number.  After some quick recalculations, I was off riding again.  At the real mile 1, the bike computer read 1.00 miles.  Not bad!  My GPS was already slightly off.  It also counted the distance I walked to the car and back.

We got a system down. I had a paper in my hand with all the counts for each mile.  I stopped exactly at that point and Blair drove up and handed me a stake.  I set it in the correct spot and rode off to the next one.  He drove the stake in and then would catch up to me.  A few of the down hill miles, I stopped a little beyond the exact number and had to back up.  The Jones Counter counts backwards if you back up so it was no problem.  It wasn't much distance past.  The bike computer only counts the wheel going around.  It doesn't know if you are going backwards or forwards.  So after 4 miles or so, it was slightly off.

We made it around the lake back to where the starting point was.  The ride was nice and the lake is beautiful.  I measured to a point at the entrance of boat ramp C where the starting line is.  I then measured to the finish line and we calculated how much of an out and back we needed to get 13.11 miles.

I went back to the point I had measured to at the entrance of the park and spun the counter back to the exact number I was on at that point.  Then I measured to the turn around point.  We marked the turn around point and had to account for the width of the road since we are having the runners stay on the right shoulder, when they turn back, they cross the road and then cross again to get to the finish.

After all those calculations I wasn't sure we would be exact.  I took the count exactly at the point where I had started.  We converted the count to miles and we got 13.112 miles.  Considering the counts per mile were rounded to the nearest whole number, that was pretty exact.  Much more accurate than the bike computer, GPS Watch, or Car Odometer would have been.

Next we had to measure the 5K.  We knew the distance from the starting line to the turn around point for the half marathon and back.  So we calculated what the difference between the half marathon turn around point and the 5K turn around point needed to be.  It wasn't a big difference.  The half marathon out and back was about 2.5 miles so we needed another .6 miles to get 5K or 3.1 miles. 

If we were going to certify the course, we should have measured the course twice and gone back to the calibration course and done 4 more calibration rides afterwards to see if change in temperature or tire pressure changed our constant.  Then if there was a change, we would need to adjust the course.

In all, I think our course is very accurate for a fundraiser run.  Probably more so than most people expect.  It was fun to learn how to measure a course and I might do it again someday but it's definitely not a new career for me.

Want to learn more?  Check out the IAAF Manual for Course Measurement.

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