Threshold for unpaved portion?

At the risk of not adding much to the discussion, I'm not sure the issue is slippage. Personally I think the front tire deforms differently on softer surfaces than it does on the hard surfaces on which we are directed to calibrate.

The question comes up "how hard is hard", and the answer is that I'm not sure. One of my experiences on a crushed limestone path on a a day when the temperature flirted with the freezing mark tells me that the same surface can be hard on the first ride and soft on the second, an hour or so apart. Another experience measuring with two measurers gave me different numbers on a dry crushed limestone path but almost identical numbers on the paved portion of that path, on the same measurement ride. As Duane states, you'd almost have to calibrate on every different kind of surface the course traversed. By the time you did that, measuring each of those with a steel tape would almost be more efficient.

If I remember correctly, Mike Sandford offered in an earlier post the in the UK there's a limit as to how much of the course can be on an unpaved surface and a bicycle measurement still be accepted. Maybe we should use that as a starting point.

I would also opine that if a cross-country course can be documented the same way that we document road courses, and it's measured with a steel tape, there's no reason we shouldn't certify it.

Jay:
The guidelines which we defined in the UK around 15 years ago are here http://www.coursemeasurement.org.uk/director-2.htm

10% max firm off road for races less than 10k. Above 10k its 500m + 5% of the race distance in excess of 10k. ie 2.6km for a marathon.

It is broadly based on the observation that off road surface can give calibrations changes up to 1%. 500m gives plenty of scope for starting and finishing a race on a playing field.

The 5% of race distance in excess of 10k provides greater margin for accuracy and also reflects a feeling that if someone is entering a road marathon he doesn't want to do a couple of miles or more on off road trails.

It just happens that this whole question is coming up for some measurement tests by a small group of measurers in two weeks time. There is a marathon with several miles on a unsealed cycle path - a former railway line, which has some rather fine but loose gravel on a compacted base. The race director wants it classified as a road race, we have refused to do so because the distance is well above our limits for accuracy. We have said no certificate - just a statement of measurement with no guarantee over the accuracy.

For the group experiment we will layout calibration courses on the unsealed path and on a nearby asphalted road and compare with several different bikes/riders/tyres.

The problem I see is one might convince oneself that this particular surface has been well enough calibrated or is sufficiently like a road that the course could be certified, but how and where can you draw a clear line between certifiable road races and cross country surface, without undertaking major calibration or surveying exercises

The advantage of the present guidelines which we issue is that it gets road races onto real sealed roads, and the question of what is a sealed road surface is usually fairly clear.

I believe a year or two ago there was a move to allow some small amount of non-sealed surface in IAAF/AIMS road races. I am not sure what the status of that proposal is. Formerly it was supposed to be all sealed roads which was found to be rather restrictive for some start/finish arrangements.

The issue is with surfaces like crushed limestone which appear monolithic but can, depending on temperature and dampness, be either very hard or very soft, so the accuracy of the calibrated bicycle method depends on the condition of the path when you measured it. Not to mention that conditions across the path can be very different from one place to another- so even setting up a calibration course on it might very well not provide an accurate calibration.

At least around Chicago, crushed limestone is the preferred surface for recreational paths that aren't paved with asphalt or concrete. Unless it's pretty wet or pretty dry it's pretty hard and I would suspect bicycle measurements are pretty true. And if I issued an edict that any course that contained a crushed limestone segment had to have that portion of the course measured with a steel tape, I can't imagine what the reaction would be.

Jay: Surfaces that get soft enough when wet for the bike tyre to sink in sound as they could effect the calibration a lot.

My greatest concern about the surface we are going to measure is the presence of small stones mostly up to about 5mm in size which you can see in this photo.


You can use the scale provided by the keys in the section, which I have magnified by 3 times, to judge the stone size.

It is worrying to note that one can see traces of cycle tracks on the path. I think that is another indication that calibration could be off.

This picture was taken close to the surface looking along the cycle path so you can see the poorly defined grass edges. These could be a problem if the path was twisty - how on earth would one then define the effective edge of the course for measuring the SPR? This particular path being a former rail track is straight for miles. But that could be a major problem on a twisty trail.

I don't know what stone is used in this trail, but when we measure on Sunday week there will be a former road engineer present so we should be able to get some expert opinion.

Rather than see our do-it-yourself work made more complicated than it already is, I'd prefer to suffer the consequences of the inaccuracy than create a complicated process to fix the "problem."

After all, it's uncommon and has little effect on the ordinary runners who are our "customers." Records are unlikely on unpaved surfaces, so this is not really a consideration here.

Mike, I believe my line of thought on this to be the same as yours- which is that if the bicycle tire leaves an imprint in the path surface, the surface is probably to soft to be accurately measured by a bicycle calibrated on a hard surface.

On the course I measured last year where the second bicycle and mine barely agreed on the crushed limestone sections, the path was on a former rail bed, but there was a failry steep slope on both sides. The curves were long and gradual so we didn't move side to side much, but exactly where the edge of the runnuing surface was could be subject to interpretation.

That being said, I can't say I disagree with Pete. Even if we are not as accurate as we might be under other circumstances, how else would these courses get measured? Steel tape? Doubtful anyone would make the effort unless it was a championship course of some kind. Bike computer? Not calibrated as well as we calibrate- and subject to the same issues regarding surface. GPS? Probably still not as accurate.

If our mission is to ensure runners are ruinning on couses that are as accurately measured as practicable, in most cases I don't think we're betraying ourselves by measuring on crushed gravel with a bicycle calibrated according to USATF procedures.

Good comments, all.

What prompted my posting of this topic is the Half-marathon and Marathon courses that are primarily gravel roads. There are a fair number out here, but maybe in the east there aren't as many gravel roads. I bet the midwest has lots of them, as there are few paved roads outside of towns.

But, on a marathon course, if there is 1% slippage, the course could be 421 meters long. That's a noticeable difference, and would justify GPS-wearers in saying "the course is too long". I'll be interested to hear from more people, if they have an opinion. I would like to agree with Pete, and lean towards 'leave well-enough alone', but I just wonder if the long courses warrant further discussion.

Duane, this discussion came to mind when I was measuring a 10k yesterday (believe it or not, temps were in the 50s on Jan. 1 in CT).
The first half mile of the course goes through a farm, following a dirt road and field trails, and it was warm enough yesterday that both were very squishy, to the point I had to walk the bike on one steep uphill. When I was finished, the start was about 180m farther than the race director had figured, using his GPS. I wonder if the surface had any effect.

I'm also reminded of measuring the course for the Rushmore Marathon/Crazy Horse Half (I think you did the revised course the following year). Last 6+ miles were on crushed stone rail trail, and I recall my rear wheel slipping like crazy, esp. going uphill.

It's supposed to be warm here, this week, but we still have ice covering my calibration course. May get out to measure next weekend, though.

I think the soft surface had a definite impact on the length, but would doubt that half a mile of soft course would yield a course 180 meters long. That's about 22% (of the soft-surface destance). On a half-mile course, I would expect a 'soft-factor' variance of maybe 2%, at most. This is based on some rides I did where I had a concrete path, next to a cinder trail. Definite slippage on the cinders of about 1%. Add mud, and maybe 2%.

I think the biggest difference is due to the GPS.

If the majority of a course is on soft surface, I am leaning towards suggesting we calibrate on the soft surface. Do a hard-surface calibration, so we have a baseline, including just a 30-meter length, so wobble is factored-in. Then, do a one-tape-length strip on the soft surface, and compare the two. A longer calibration would be preferable, but may not be practical. Calculate the difference, and adjust accordingly.

While (as Jay said) records may not be set on these courses, it would still be a better product if we made the effort to make them the proper length, not just fall-back on "at least as long as the stated distance", and have a course such as this 1.7% long, instead of just .1%. (I subtracted the SCPF from 180m, since, in a perfect world, the course would be 10 meters long, anyway.)

Thoughts?

Amazing to me that this topic jumped up today; yesterday I measured a course on the C&O Canal, and I was mulling all these things over as I did the work. Here's a comparison of calibrating on the street vs. the towpath. I have a newly laid-out 300 meter course a couple blocks from home, and a course on the towpath near Carderock, Maryland that I measured in Nov. 2009 (length 1046.83 ft or 319.07 m; course # MD09010RT).
Date Time Temp Cal Course Constant* (counts/km)
12/31 3:16 pm 55 F First Street 11236.67
12/31 5:09 pm 52 F Towpath 11223.24
1/1 7:41 am 41 F First Street 11242.50
1/1 8:42 am 39 F Towpath 11221.99
1/1 11:30 am 52 F Towpath 11216.97
1/1 12:46 pm 59 F First Street 11234.17
(*Constant is before multiplying by 1.001)

Based on the calibration, I felt I had enough information to be guided by the towpath constant rather than the road constant. But not totally, for some of the reasons Mike Sandford was stating: the towpath is not exactly the same for its entire length. My cal course is on a straight, hard and kind of bumpy stretch, but there are parts that are smoother and softer (not much real mud this time).I ended up using 11240 as a working constant, this to jibe with the longest of my towpath calibration rides rather than the final average. Probably the 20 km course is a little longer than it needs to be, but not obscenely so. I had previously marked a turnaround based on an existing half marathon, which in turn was based on another half marathon, so when I found that tentative turnaround only 39 counts beyond my planned turnaround spot I felt that it all tied together pretty well (I used the previously placed point).
I agree with Pete, let's not worry about these courses being too long. I'm in favor of calibrating on like surfaces but I think this example shows it wouldn't have been disastrous to use the road calibration.

Technical question, can someone tell how to include a table for a submission? I made a little table, tried to copy it but then found it was kind of screwy. So I made it look "right" in the little message box-- but now it is kind of run together.

I don't know of any way to type in a table that lines up well after posting on the forum. Instead, I capture part of my screen showing the table in Excel or whatever, and then post that image on a website and link to in on the forum.

We measure the course for the local HS cross country championships each October, adjusting the start to bring it up to the official distance. The calibration is done by riding on the grass alongside the 110m straightaway of a nearby track. A quick & dirty way to calibrate on the same surface as the majority of the course.

Alert readers want to know: did you compare the counts on the grass vs the counts on the track?

Bob, I don't do the measuring for this course, so I don't know.
But when it's next warm enough, I'll do an A-B-C comparison (asphalt-grass-track). Might get yelled at as they just resurfaced the track - I'll have to wear my IAAF Measurer's vest.

Jim, It would be interesting to do that with a measuring wheel too.

Phil Holland and I have done some work on measurements on the Stratford Greenway, which I photographed for a post earlier in this thread. The Greenway, a former railway track, has been converted to a cycle/walking path by spreading crushed limestone. The surface is quite good, but it is not a sealed road and has small loose stones.

From our report (pdf) report you can see that our gravel calibrations were in good agreement with those on a nearby road:
Phil: -0.014%
Mike: +0.006%

Our measurements over a a total of 4 km of the Greenway differed from one another by around 0.05%, probably because our two tyres responded differently to the varying roughness.

More worrying was the fact that the previous measurer of this course had in 2008 obtained much larger values. His results had been about 0.13% larger over a smooth section and 0.45% larger over a rougher section.

We think there has been no mistake in identifying the reference points so wonder whether the surface has changed over three years.

Phil prepared a paper for a recent meeting of our Course Measurement Working Party. He suggested that we might institute 3 levels of certification:
1 Road courses.
• Sealed road or pavement - less than 5-10% other surfaces.
• Issued with a Certificate of Course Accuracy showing compliance with IAAF
requirements for road races.
• Logo wording is CERTIFIED ACCURATE.
2 Gravel courses.
• Sealed road and/or good compacted gravel - less than 5-10% other surfaces.
• Issued with a Certificate of Distance confirming a full-length course, but not
claiming to be comply with IAAF limits of accuracy for road races.
• Logo wording suggested – DISTANCE CONFIRMED
3 Off-road courses.
• Over 5-10% on surfaces other than sealed road or good compacted gravel.
• Issued with a Statement of Course Measurement confirming the measurement
method used but stating that 'the distance recorded is measured only as accurately
as the definition of the course and the course surface permits'.
• Logo wording is MULTI TERRAIN.

No action has yet been agreed. Discussions continue.

I have made a webpage at http://coursemeasurement.org.uk/offroad.htm we plan that it should hold photos of surfaces as a guide to measurers, and also report further comparisons measurements as these are undertaken.

Is the use of non-paved courses or sections of courses is a real problem for us? I have measured about 10 courses over 20-years that were not entirely on paved roads. I have measured but refused to obtain certification for a few others because they had sections of un-paved road or path with un-defined edges. I have also obtained certification of a couple courses using a steel tape for the unpaved (grassy) sections. These sections were fairly long (>500-ft) and required the use of pins to obtain the shortest route.

The most recent example of a course with un-paved sections is a half marathon with 2 dirt roads totaling over a mile of the course length. These roads are traveled, graded, hard dirt with stone walls or ditches on the edges (well defined edges). I didn't use a different constant for the dirt roads as they are nearly hard as the paved road. The dirt road surface is of different and varying roughness compared to the paved road. This would probably account a difference in constants, but the variation of dirt road roughness would make calibrating on the dirt impractical.

Although Mike Sanford's 3-level idea doesn't address repeatability, it could be a solution if there really is a need for one. I'm sure that a set of RRTC rules for measuring, reporting and checking would need developing for such an approach.

Mike, I have not heard of the "Course Measurement Working Party". Are they well-represented in Parliament?

Guidos, I don't look at this as a problem begging for a solution, rather the discussion is to make measurers aware of the differences in measurements on paved vs. non-paved surfaces.

If calibrated on pavement, a measurement on non-paved surfaces will be longer than our click-counts would indicate. If we are interested in not only assuring that a course is "at least as long as advertised", but also assuring that the course is accurately measured, then we need to be aware of the variance.

Unlike you, we have plenty of gravel-road courses out here in the unsettled west. I have not had to measure one in the last two years, but prior to that I did 5 or 6 half-marathons and marathons on gravel. In hind-sight, they are all likely to be way over our SCPF long. Based on comparisons I did two years ago (concrete vs cinder trail), the Half courses could be 200 yards long, or worse, and Marathons even longer. I don't want courses to be long just because they are on gravel.

I would suggest that people calibrate on the dominant surface of the course. If I do any more gravel courses, I will tape out a calibration course on the gravel (or cinder rails-to-trails) surface, and not rely on an asphalt calibration. Just interested in accuracy of measurement, not just going through the motions of calibration, measurement, and having the course longer than our SCPF.