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If you measure on grass, you must calibrate on grass.

This exact situation is being addressed and will likely be finalized at the National Meeting in December. It appears that if a course contains more than an insignificant unpaved section, that section will require bike calibration on that or a similar surface. 

Obtaining a reliable measurement on grass is one of the reasons Cross Country courses are not eligible for certification.


Jim, in 1976 I measured a cross-country course. I calibrated on our road course and then calibrated on a calibration course (800’ in length) on the grass. The calibration figures were: 15771.5 counts/mile on the road and 15614.8 counts/mile on grass. You can see I had more revolutions of the bike wheel on the road than I did on the grass. If I used the road calibration when measuring the XC course, I would have ended up with a short course. The difference is about 1.0%. I should mention that the calibration course was not level. It was not possible to find a level stretch. I recorded more counts on the uphill runs than the downhill. I think this is because my weight was forward on the uphill runs making the bike tire sink more into the turf.

I think you should calibrate and measure on the same type of surface.


Alan I believe you have it backwards. If you had used a larger calibration constant (the one from the asphalt calibration) it would have resulted in a longer course. You would have had to travel further on the course to get to the 1-mile mark on the course if you were using a larger constant. We always use the larger of the pre-cal and post-cal constants because the larger one results in a longer course, right?

I seem to remember that this was the experience of several measurers in the past. That when they calibrated on an unpaved surface they got a smaller cal constant than when they calibrated on pavement. Because of that there wasn't that much concern about calibrating on pavement before measuring an unpaved course because it was expected to result in a longer course.

Jim, the rear wheel might slip on a lower friction surface, because the torque you apply when pedaling might be a stronger than the torque resulting from friction with the ground. But this is very unlikely to happen with the front wheel. It doesn't require much friction force to get the front wheel rolling because the only thing really resisting that rolling motion is angular inertia. And once the wheel is rolling, you don't need any friction force to keep it rolling. So it's unlikely the front wheel would slip rather than roll along the surface.

I believe the real reason different friction values can change the cal constant is because it affects how much the flattened section of the tire changes its length. If there is no friction there is no force to change the length of that flattened section. So even though the tire flattens, it also spreads out, and the effective circumference of the wheel is not changed. On pavement the friction is very high, and I think it results in a "stick" condition, so that flattened section is shortened quite a bit (from an arc to a straight line). Any surface that has lower friction is going to shorten the flattened section a lesser amount, and that means the effective circumference of the wheel will be larger (and thus a smaller cal constant than you would get on a high friction paved surface).

All that being said, I think grass is much more complicated and problematic. As Alan mentions, the grass surface will deform under the wheel. Any theoretical calculation of how that would change the effective circumference would be very complicated (and probably wrong!). The big problem though, is that there is a huge variation in grass surfaces. You could calibrate on one grass section, but then some other section of the course where the grass is longer, or thicker, or a different variety, could have a very different cal constant.

Pete Riegel somewhere wrote that calibrating on pavement and measuring on a trail was most likely to prevent a short course.

  I did a direct comparison once:  Pneumatic and airless tired bikes calibrated on pavement and then on a trail surface.  Then measured a course with both bikes.  Then recalibrated both on trail and pavement.  Yes, it was a long day.  I thought I could see a lot more particulate adherence to the tires in the early morning dampness than in the hot afternoon when the surface dried out.  The airless tire recalibrated about the same. The pneumatic did expand but not as much on the trail as on pavement.  Normally, the airless tire barely expands during a typical day's 20 F heat up.  Based on that, I agree with Pete that a pavement calibration course is much more reliable / repeatable than a trail calibration course.  If you don't want the trail or grass course to be long, wait till it is dry in the afternoon to measure.  

We have measured several courses that had "not insignificant" grass or dirt segments .  For the first few (CT13038JHP, CT13018JHP and CT10040JHP), we measured a 300-Ft cal course on the dirt or grass and determined a dirt or grass constant.  The idea being that if the dirt or grass constant was larger than the road constant, we would layout a 1000-ft cal course on the dirt or grass and use it for the "not insignificant" segment.  We stopped doing this after 2 or 3 times as the dirt or grass constant was always smaller than the road constant.


Pete Reigel did write that, as Oscar noted, that calibrating on pavement and measuring on dirt or grass would prevent a short course.  Also, didn't Mike Sanford do a very complete study of the impact of calibration course surfaces on the constant (therefore the measured course length)?

All good arguments against certifying cross country courses.  However, the argument gets cloudy quickly when the course is a hybrid, road, trail, dirt path, grass or combination.  I think the RRTC isn’t helping measures with less than definitive rules.  In this case what is “not insignificant”?  A 10K with a 1–mi dirt section with defined edges and or repeatable features properly measured will not result in a short course.  That used to be our goal - within reason

"At least the advertised distance" is no longer the rule. It was decided a few years ago that all courses must be certified at whatever distance their measurement came out to. So it is no longer the case that a course that is measured to be 5040 meters gets certified as a 5k. It gets certified as 5040 meters.

I agree, Mark. Remember we once contemplated "How long is too long"? What was the upshot of this? I haven't yet seen the rule, but I may have missed it - was some definition of an "upper limit" defined?

For instance, we sometimes find ourselves concerned about how a particular race organization may or may not do a satisfactory job of course layout. So, we assume that some of its participants may run the tangents despite the RD's assurance that he will place a line of cones down the middle of the road to keep runners on a single side as they run both directions on a stretch. So, we measure the full tangent. If the cones are laid out and runners stay on one side or the other, then they are running longer than the measured distance, but not shorter. So, we consider that we have done our job - right?

Now, consider a course such as G.B. mentions, with a long unpaved section, but now without defined edges or repeatable features. Most of us have encountered these, right? Could we, in theory, at least, measure such a section, assuming no nearby tall buildings and good sky view, using GPS coordinates to define the path and the timing points? We could, again in theory, it seems, calculate the largest likely error distance of each recorded GPS coordinate based on the particular average error distance of the instrument we use to obtain readings, add up all of these variances, and extend the course by this amount. The course as run might be long, but maybe not much more than in the example of a road course divided by a traffic cone line, right?

Yes, I am engaging in "devil's advocacy" with these questions. With a purpose. For instance, I once mentioned on this forum a particular event in which several national records have been set. A validation measurement revealed the course to be over 45 YARDS long. This creates an unsatisfactory situation in which another race of the same distance, validated to say, 12 inches long, could produce a faster record performance by a slower run, right? The "long" course in question is advertised and certified at the same distance as the one validated at 12 inches long. Now, 45 yards at a national-record pace is only a few seconds. But I argue that this record discrepancy is real, not theoretical. 

My purpose here is twofold:

1. In the real-world case of the event referenced above, the course is not certified at the measured distance. It is certified at the nominal standard distance. A validation failure is a situation that none of us ever want to be in, obviously. My sense is that the measurer knew that this event had produced national records, even one world record, and he essentially "padded" his overall distance so that there would be no chance of a validation failure. If we measure a course to be longer than the advertised distance, and certify it for the measured distance, should we have some kind of upper limit past which we should not support the naming of an event at the (different) nominal standard distance? This is another version of the "how long is too long" question. Is this unimportant, or should we have some % standard?

2. I am on the side of at least some XC courses being certifiable. My reasons are partially explained by the arguments above. These arguments are supported by the fact that calibrating on paved certified cal courses, as we do, then measuring on an unpaved course, tends to produce slightly longer courses. If we are OK with a divided-road course potentially being long, we shouldn't be averse to an off-road course being equally long - right?

This discussion tends to lead me into a separate, if related topic - measuring off-road courses. Rather than invoke a reprimand by our esteemed Admin for conflating or discussing multiple topics in a single post,  I will post some thoughts on a different thread. 





The question of how long is too long was answered at an annual meeting a few years ago. It was decided that any distance long is too long. A course must be certified at the distance it is measured. If the RD has particular spots where he wants the start and finish to be, and you measure the course with those restrictions to be 5040 meters, then it must be certified at 5040 meters, not 5000.

There is a HUGE difference between people in a race running more than 5000 meters because the RD did not follow the certification map, and those people running more than 5000 meters because the course measurement was inaccurate.

Fair enough, Mark. I still see a large amount of wiggle room in this policy. Again, I reference the type of course with two-way traffic. I know there isn't unanimity among RRTC folks about whether to measure only on one side of the road in each direction or, alternately, to measure the full road tangent. I measure the full road tangent unless the certification is for a major race in which I am confident that the course layout will prevent runners from cutting the course. This reduces the number of courses in which I don't measure the full tangent to like - one. I am aware that as certifiers, we do not, strictly speaking, assume any responsibility for how our certified course is set up or managed on race day. But, I have come to expect that many races do not understand or care about what we tell them, if we even bother, about how to ensure participants run the certified route. Each time we measure the full tangent in this curvy road situation, we encounter the likelihood that, if course layout is done properly, we have certified a course that is long. The more curves in the road, the greater the potential error. I suspect this is one contributing factor in that event with many record performances I referenced. 

I always take an activist role in this. For some races I even show up and help with or consult on the course layout plan and execution. It seems to me that doing this differently, leaving the actual path to be run totally up to the race organizers to recreate, can easily lead to a short course being run in these circumstances. Am I right in saying that we have a baked-in bias for ensuring our measurements are always at least the nominal distance, and far less concern about whether they are long by some non-trivial amount? If we do, I for one, am fine with this. But, I am convinced we certify few if any short courses - ever - maybe none at all - and, plenty of courses that are long as actually run. Some, long by a non-trivial amount, because we cannot unilaterally control how any course is actually traversed by participant. I am interested to hear the experience of others, with respect to knowing that some course he/she certified may be longer than the standard distance by some non-trivial amount.


Long Course vs. Measured Course - Probably doesn't belong in this thread (Difference between cal and course surface)  however there's some good discussion to be had here.  Let's talk about a course (accurately measured) with 2-way runner traffic.  I think the Measurement Procedures Manual, Shortest Possible Route chapter provides sufficient guidance.  I know it has for us. 

If a race director proposes a course with 2 direction runner traffic, especially on a non straight section, we always inform him that that section will have to be coned to prevent runners running less than the measured distance.  If the RD agrees, we measure a restricted route (one side, one way; the other side, the other way) and show and state the restrictions (location of cones) on the map.  If the RD does not agree to cones, we measure the shortest, unrestricted route.  In the second scenario, the RD has  created a race where the runners (especially the lead runners) almost certainly will run longer than the measured distance.

This is a dilemma I don't think the RRTC or the measurer or Certifier can reasonably resolve without reams of regulations and, ultimately, lawyers.  I feel that we (the measurer) has done due diligence by informing the RD that some runners may run longer and offering an alternative.  

What are the consequences of measuring (accurately) the shortest unrestricted route, knowing that some runners will have to run longer than the stated distance?  Any record set on the course would still be valid, assuming all other conditions for records are met.  The course could still be successfully validated or verified.  The only negative consequence is the possible lost opportunity of a record performance.  This is clearly beyond the jurisdiction of the measurement community as the possibility of a record always exists and always can be lost.  This of course doesn't consider runner complaints of long course or unfavorable opinions about the race.  These are not the measurers' concern, especially after due diligence and accurate measurement.

By the way, I agree and always have that a course measured at 5K must be certified as 5K.  In this case the "5K" is the "advertised distance" that I referred to.  Sorry for any confusion on this point.

Another by the way; I believe it is far beyond the responsibility of the measurer or certifier to check every (or any) USATF certified course set up on race day.  That is the job of the RD or the RRTC if the race is a USATF Championship.

I would be surprised if your approach isn't the same or similar to that of most measurers, G.B. In the two-way traffic on a curvy road scenario, another dilemma occurs when the RD agrees to split the road with cones, we measure on both sides, then the RD doesn't follow through. And I have witnessed lead runners take the tangent in and out of a cone line. In either of these instances, a short course is run. Any record performance would not survive a validation.

Maybe there is nothing that can be done about this for most events. For the 30,000-participant Army Ten Miler in D.C., Bob Thurston and I are hired every year to monitor and supervise the course layout. This is a big and sometimes colossal job. Though all the soldiers who nominally put out the thousands of traffic cones work with detailed cone maps, Bob and I expect to put in two hours of cone work before the start, and sometimes more during the race. In almost every edition of this event, had we not been there to direct this operation and then maintain the layout during the race, the course would not have been run as measured. A couple of years ago, Bob ensured the cones defining one particular 90-degree left turn were placed appropriately. He then moved on to another part of the course. As he swung back by this intersection later, he discovered to his dismay that someone had taken it upon themself to move dozens of cones away from this turn and place them on a different street. A few of the lead wheelchair/hand-crank athletes took the wrong turn before Bob could fix this. We learned later that a "helpful" police officer had an out-of-date course map with this turn going up a different street. Had Bob not been there to rectify this, the race would have been run on a substantially different course. Any records would have gone out the window. Had this been a money race, and had some runners had taken one turn, and some another, this would have been a disaster.

I do not know how many large events employ someone to ensure the course is laid out properly.  I conclude that there must be some magnitude at which every large race must have involvement by certifier(s) to guarantee the course run is the same course that is certified.

I agree with most of your observations.  We also have been hired as course marshals for some races.  One of our largest clients has a "Technical Director"  who is the course marshal for all their races.  We work very closely with him before and during measurement and he is present at the races.   The certifier has never (to my knowledge) had any role in checking the course layouts on race day. 

As to the magnitude at which the certifier becomes involved, I believe that would be any USATF (National) Championship race.  There are rules about a qualified validator (not necessarily the certifier) being on the course (in the lead vehicle) on race day.  Mike Wickiser is the guru (Validation Chair).  This is nicely covered on the "Verification" page of the "Resources for Event Directors" page on the USATF website. 

These championship races are a tiny fraction of the races held on USATF certified courses.   The vast majority rely on the integrity and professionalism of the race director to insure that the racecourse is the course that was measured and USATF certified.

Admin posted:

The question of how long is too long was answered at an annual meeting a few years ago. It was decided that any distance long is too long. A course must be certified at the distance it is measured. If the RD has particular spots where he wants the start and finish to be, and you measure the course with those restrictions to be 5040 meters, then it must be certified at 5040 meters, not 5000.

There is a HUGE difference between people in a race running more than 5000 meters because the RD did not follow the certification map, and those people running more than 5000 meters because the course measurement was inaccurate.

So, the 5040 meters certification can still be called a "5K" on the certification map, and on the race advertisements?

We have a justifiably small margin of acceptable error between two measurements. So, why not establish a similar criterion for "too long"? I like .001. 1 meter per kilometer. If a 5K (with SCCF) is measured at more than 5005 meters, it is at least 16 feet long. This seems to me be a good cutoff point.

If this course were submitted for certification as a 5K at 5040 meters, we would certify it at 5.04K. Would we still want to call it "5K" on the map? How would we categorize it in the certification database? Entering "5K", then "exactly" in the database search field wouldn't show this course.

The course name on the map should not be the important feature.  We always put the actual distance certified under the course (usually the race) name.  If the RD wants the name to be JOE’S 6.3-MILE RACE, fine.  Right under  JOE’S 6.3-MILE RACE, the map says  “3.106856-Mi (5K)”  and the certificate says the same.  I don’t think we need a rule on naming.

I would agree if I could, GB. Truth in advertising has been a problem with too many races. Which is part of the reason our profession exists, right? Years ago, a 5K race in my region became very popular because so many participants ran P.R.s. Only a few savvy runners questioned the course distance. A few bugged the R.D. to get the course certified. When I measured the old course, it was only slightly over 2.9 miles.

I'm all but certain many of us can cite similar stories. If Joe advertised his race as 6.3 miles, and participants ran a certified course at 3.10686 miles, can you imagine the bedlam at the Finish line?

On the original topic, I will throw in that I have done two more direct comparisions with an airless tire and both times, pavement calibration was significantly more counts per mile than unpaved surface calibration.  Looked back a ways and there was one that was dead even.  Has anyone ever done a direct comparison where unpaved cal counts were MORE than paved counts?

Thanks for that additional info Oscar. I think a lot of people are considering using airless tires, including me, so it's nice to have that input in technical discussions for the airless tire case too.

Mike Sandford did a lot of excellent work comparing calibration constants on different types of paved surfaces with different types of tires. I don't think he ever looked at unpaved surfaces but I could be wrong. You can read these reports by going to, scrolling to the bottom, and clicking on "Measurement News Article Index." Mike's articles on this topic are in issues 75, 89, 90, 91, and 96.

"Slippage" of a non driven wheel?  We've been hearing for years about "slippage".  We've heard "slippage" is why we don't measure in the rain or on wet roads.  What would make the front bicycle tire slip, except to the side (maybe while turning the handlebar)?    There was a good discussion of "slippage" above (on 10/21/2018).  We need to slide off the "slippage" excuse.

Mike Sandford and others have shown that rougher road surfaces result in longer measurements than smoother surfaces.  This is for paved surfaces.  It can reasonably be extended to hard packed (or frozen) non-paved surfaces, but not to grass (again see the 10/21/2018 post).  Maybe it will hold for grass on frozen ground.  This rapidly becomes a huge science experiment, well outside the "everyman is a measurer" concept.

Bottom line, our policy of not certifying cross country courses is probably a good idea.

I contend that most any XC course measured with our certification methods will at least potentially be much closer to the "actual" distance (where a steel tape measurement is the standard) than the measuring wheel commonly used to set up high school and college XC courses.

First, as Mark Neal has shown, measuring wheels, even when carefully guided along course tangents, is insufficiently accurate to the advertised distance.

Secondly, I have learned that visualizing and riding/guiding along course tangents is less intuitive than I might have expected. It seems to me that some people with lots of experience directing races have little or no ability to see the SPR on any given course, with or without a measuring wheel.

Finally, if the cal course for an off-road course measurement is set up on the same surface as the course, and the course is measured as a series of segments with each locus clearly identified with respect to nearby fixed objects, I submit that such a course, as measured by an experienced certifier, would stand up to a steel-tape verification.

One problem is the "nearby fixed objects" if the path changes direction through an open field with no such objects around. Oscar and Mark have shown that our civilian-grade GPS apps seem to have too much variance for GPS points to be relied upon.

However, when a course to be measured has plenty of such objects, I maintain that a valid course can be measured and mapped. Such a course will be more accurate than anything other than a steel-taped course, IMHO.

A friend recently bragged about his young grandson running 14:10 for a 5K XC event. After congratulating him, I asked what this time indicates, since "5K" XC courses are not certified, may or may not be accurately measured, and tend to differ in length by non-trivial amounts. "Of course", he didn't respond.

My running club, MCRRC, advertises and conducts a "5K" XC on a course that I conclude is barely 3.0 miles. No one cares. I'm willing to bet that, if this course was "in reality" closer to 3.3 miles, most everyone would then care.

Even if USATF allowed cross country courses to be certified, there would be very little demand for it, at least in high school cross country.

The reason is that the number of interested parties (the runners, parents, grandparents, some coaches, and some meet organizers) that want the course to be called 5k but be short, greatly outnumber the interested parties (some coaches, some meet organizers, and all measurers) who want the course to be accurate.

I wholeheartedly agree, Mark. As I explained to an RD who recently advertised his XC race as 5K when I know for a fact - I measured a partially concurrent 5K on the same piece of park real estate - few people concerned, if any, seem to care. I view this fact as an artifact of the history of poorly measured XC courses being the accepted norm.

Jim, I for one am willing to bet your CT XC course would stand up to a steel tape check.

IMO, if we were to create a different category of certifications - say, a "conditional" category, with the condition being that full certification status would be granted only by a steel tape verification or by some newer, well-validated technology like lidar or something yet devised - we would then potentially create a new standard that would make XC race performances somewhat comparable to each other. These courses would then all become the expected standard over the coming years. Most if not all of these courses would be more accurate than the previously used courses.

Jim, to me, your method for the CT HS championship makes perfect sense. Given (1) the modest investment required by organizers to create a reproducible course with your methods, (2) the comparability with other courses your method affords, (3) the improved accuracy of XC courses across the U.S., and (4) the 10 year life span of the provisional certification, I see no a priori reason we shouldn't contemplate a new, "Cross Country Certification" category.

Jim, I think state meets are the exception to all of this. State meets don't have to have a "fast" course in order to attract large numbers of teams. Invitationals during the season where a large percentage of the runners set PRs get a huge number of teams that come back year after year, because they have a "fast" course. Invitationals where kids don't set PRs, don't. That's just one of the big headwinds that will be encountered by any effort to get large numbers of HS XC course accurately measured. Cost, of course, is the other.

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