Wheel calibrations

Interesting experiment. Pretty much what you expected for results, isn't it? Other than the consistency, which is surprising.

Any idea why Wheel 2 seemed to measure shorter on the grass than Wheel 1? Was it lighter, so it slid across the grass more?

Thanks for the report. It shows that at least some people can get a good measurement with a wheel!

It's possible that the direction effect could be that I managed to keep a straighter line in one direction than I did in the other. I hope not. The fact that I didn't see that on the paved course indicates to me that it isn't that hard to keep a straight line.

The two wheels were very different. Mine is a cheap plastic one with a continuous gear drive, and the one I borrowed was a heavy steel one with a clicker every meter. I don't know what causes the difference on grass but I have no doubt after this that it is real. Slipping could be a factor but so could the fact that you are deforming the surface you are measuring on the grass. Pushing down harder to avoid slipping may actually make things worse.

> It shows that at least some people can get a good measurement with a wheel!

I would venture to guess that in the history of the sport of cross country no one has ever calibrated their wheel before measuring their course.

I measured a high school course a couple of weekends ago and I pulled a steel tape over it.

I still think when you're measuring over an unpaved surface the wheel picks up irregularities in almost any surface that a runner won't necessarily have to deal with. Every irregularity, whether up or down, adds counts (or fractions thereof) to the wheel measurement, and those give you a longer length than you should get. The tape is largely immune to that.

I don't think deforming the surface is that big of a deal. For all practical purposes, the earth is the same diameter at the bottom of the deformation than at the top, and I can't imagine the surface is hard enough to deform your measurement instrument.

Interesting.
Which data table was with the heavier wheel?
Some observations:
1. Some xc courses are run on golf courses but many are over various terrain -dirt, non-manicured grass, exposed tree roots, pebbles,etc.. You would most likely get a greater variation if you measured over these surfaces.
2. A big problem is keeping the wheel straight. Fatigue sets in and the wheel will begin to wobble.

Wheel 2 was the heavy wheel, but I was applying some downward pressure for both of them.

We held our league meet yesterday. One of the coaches measures the course each year. He calibrates his bike by riding alongside a nearby track on the grass between the 100m start and the finish line. Not quite the required 300m, but for XC courses, I think good enough, and based on experience I think the calibration surface is more important than the actual distance.

That's a great idea! If he has a Jones, that should work fine for a 5k X-C course. If he is using a cyclometer, if it goes to 3 decimal points, that should be pretty close, also.

Yep, he uses a Jones.

I suspect how accurate his measurement is depends on how consistent the surfaces are.

When I measured the course in Peoria in 2008, there were hard spots and soft spots and tall grass and grass worn away, etc. And that was using the first 300 meters of the race course as a calibration course. It's very difficult to calibrate on the same surface you measure on.

I suspect his method is more accurate than using a measuring wheel, though, and to insist on the use of a steel tape would be foregoing good in pursuit of perfect. Or something like that.

True. He calibrates on grass, and the majority of the course is also on grass. There is about 1 km on dirt trails, however. The whole thing about XC records is they're relative, not absolute - you can compare times on the same course, but not between courses, even of the same distance. Since the winning boy broke the course record it's nice to know the distance has been measured consistently year to year.

I'm not sure that's exactly true. And even if it is true, you can't stop coaches and runners from trying to compare times from course to course.

I think if you were to assemble enough data, you could probably develop formulas that compare performances on different cross-country courses. The length of the course, while important, wouldn't be a factor in the equation, however.

In Illinois, the state meet course has been in the same place- Detweiller Park in Peoria- and essentially has been the same course since 1971. Other courses are rated (informally and unscientifically) as being x seconds faster or slower "than Detweiller".

The problem is that while Detweiller has stayed pretty much the same, other courses haven't. Park districts build fitness centers or turn start/finish areas into revenue producing soccer fields. And if the other courses change every couple of years, you can't assemble enough information to develop a robust conversion formula.

Jay, someone did this for some of the major courses in the U.S. (Van Cortlandt, Franklin Park, etc.) using Purdy Points to come up with each course's difficulty in "virtual meters." So rather than comparing by time, a course is determined to run x meters longer or shorter than another. It's an old site, but still relevant, I suspect.

Cross Country Course Ratings

Going back to a post from 2012 re: using a track to calibrate bike [with Jones counter] - for measurement of XC course.

Curious if this is a reasonable method or is established road process recommended.

Any new/other best practices?

The course we've been asked to measure starts and finishes on the track.

quote:

Originally posted by Jim Gerweck:
We held our league meet yesterday. One of the coaches measures the course each year. He calibrates his bike by riding alongside a nearby track on the grass between the 100m start and the finish line. Not quite the required 300m, but for XC courses, I think good enough, and based on experience I think the calibration surface is more important than the actual distance.

In my view, if it's an XC Course that would be ok. However, we would don't issue a certicates for XC Courses.

Thanks for the quick reply Gene -

Understood - XC courses can not be Certified.

I'm looking for the best practice/option to provide an "accurately measured" course.

Thinking that using a bike would be preferable to a wheel. Keeping constant and uniform pressure on a wheel for 5K or more would be difficult.

quote:

Originally posted by Gene Newman:
In my view, if it's an XC Course that would be ok. However, we would don't issue a certificates for XC Courses.

Mark, if I understand your data, it seems to bolster Bob Thurston's contention that calibrating on pavement typically if not always results in a slightly long measurement on grass. If this is accurate, it seems to me there could be a way we could establish criteria for a new category of course measurement.

Instead of issuing a certificate, we could issue an informal "letter of accuracy" or something similar. The criteria would actually be stricter than for road courses, since the measurement path would have to be painstakingly defined and documented.

Current GPS instruments record single points with good accuracy when there is clear sky view. With sufficient points identified, it seems to me the measured course could be accurately recreated for race day. Stream hops and blow downs could be measured over with a steel tape with no loss of accuracy.

I have measured a few XC courses in which I took great pains to document dozens of points to define the measured path. I would be willing to wager that all of these measurements could stand up to a rigorous tape pull. In fact, I would be surprised if they aren't all at least a few yards long.

I think we would not want to start a new official category like that; it would come to be seen as a "certification", just with a different name.

As much as I like the idea of "pinning down" a course as you did for some of those XC courses (and as I was all in favor of!), I'm now wondering if any XC course managers-- other than nerdy course measurers like us-- would ever actually bother with all the details that would be required?

Just practically speaking, maybe it's best to measure a course each time it's run (or once for the XC season) to make sure it's right. Or just set it up and run the event, but don't make any claims about accuracy. Just my thoughts.

I was wondering if my post would renew the "certification" discussion.

From a purely logistical standpoint - how are most XC courses measured? I'm pretty new to this gig and am looking to offer our local HS an "accurately measured" course.

I'm not so sure all of the HS cross country race directors out there want their courses to be accurately measured. Just sayin'

Mark is correct. I coached HS and College XC and found that their only concern was with year to year comparisons of times on the same course.

I offered many times that I could make their course relatively accurate, but the answer was we want to leave it as it has been for the last 20 years.

However, I my home course was measured with a JR Counter and it was close to the advertised distance.

To respond to Andrew's question I think most XC courses are measured by a coach with a measuring wheel. Probably in the middle of the path or where they think runners would run, and without any SCPF.

I am more comfortable measuring with a calibrated bike, following SPR and using SCPF-- but per Mark and Gene's comments, I'm not sure if these efforts are appreciated or resented!