Wheel measurment question

Thank you to all the course measurers/certifiers who took the time to reply to my query. I sincerely believe that you guys and gals are a dedicated group who take great pains to ensure that race courses are accurately measured. Another Measurer, thanks for the offer to join your ranks. I'm afraid that at this point in my life, I possess neither the bicycle skills nor the time to devote to such an endeavor.

I realize you measurers and race directors are besieged by an army of GPS wielding runners, who wave their Garmins at you and tell you that you have done your job incorrectly.

I believe it is the pride you take in your work that causes you to rankle when someone posts yet another question about inaccurate courses based on GPS readings.

If you re-read my original question on this thread, you will find an underlying assumption that courses are measured accurately with calibrated Jones counters. My concern was that after the precise measurement of said courses, that there may have been abuses of the SCPF. I believe my uneasiness about the SCPF goes back to when it was first introduced, in the early to mid-1980's. Suddenly, courses in NJ that I had run every year were getting longer, not by a barely perceptible 0.1%, but by as much as 15-30 seconds on a 10K. This was long before the widespread use of GPS devices. The only evidence for the lengthening of familiar courses was that nearly everyone was running slower times on those courses, and that starting lines kept creeping further and further back. Now with GPS devices and mapping sites, one is able to at least get an idea if a course is grossly off.

I mentioned an instance of a recent 5K in an earlier post on this thread. Another example was a 10K, also within the past month on a course with which I am very familiar. I did a training run on the course and found each mile to be not just a barely noticeable five feet longer than what my Garmin 305 showed. The mile marks were consistently 25-30 meters beyond what I measured. In fact, they were so consistent in their excess length, that I just assumed the SCPF had been applied. At the end, the Garmin read 6.33 (and I cut the tangents pretty tightly). Gmaps gave me the same reading. In both cases, I had maps of the courses available to review.

I guess this is starting to sound like yet another whacky conspiracy theory, but I would appreciate it if anyone familiar with the certification of NJ courses would assure me that they only use the same .001 SCPF that is used everywhere else. Thanks again everyone.

thanks for your input

good to know, if you are indeed in the know

is this really Steve Martin?

I just saw your movie being replayed on Comedy Central...

"the new phone book is here! the new phone book is here!"

You should pass on your knowledge to all those clueless females that ran the white race at Terre Haute and are strutting around bragging about their new sub 20 minute and 21 minute 6km PR's because the course couldn't possibly be just a wee bit short (say 30 to 40 seconds) and their coaches don't want to break their hearts or burst their balloons by telling them the truth.

This is an interesting thread and I would like to contribute my experience. As an elite walker I have participated in literally hundreds of National events where the courses are “certified” to not be short. To my knowledge and experience I have never walked a short course BUT I have walked “certified” course that are beyond the length of the short course protections. I routinely use a meter Gandy wheel which I check/calibrate to the track. Since Most racewalking loops are 2 kilometers; I walk 2 kilometers on the track and the Gandy wheel Always come up within a half meter. I the use the same wheel and walk the course twice both ways and I often find that these walking course are as mush as 10-15 meters LONG per loop. Over 20k this can ad up to 100 to 150 meters long; enough to cost an A standard. Here are some things I know:

1) Those who believe in the Jones Counter as the most accurate method of measure staunchly defend it to their death so much so that I become suspicious automatically.

2) ) I have talked to several course certifiers who will tell me that they do not know how long a course is only that it is not short.

3) My Gandy wheel, while not the most accurate, is consistent time and again.

4) NO Cross Country course where the men’s and women’s start are the same and the finish line are the same is ever what it is advertised to be.

5) And finally if the idiots’ who layout the course don’t put the cones where they are supposed to be (and this has happened) it doesn’t matter how you measure the course.

Not sure what a "Gandy wheel" is but I assume it's some kind of surveyor's wheel.

How do you calibrate it on the track? If you walk a lap w/ it, trying to maintain the proper distance from the curb or inner lane line is a bear, so I question how accurate that might be. Also, is has been examined in some detail that different surfaces have different friction coefficients and thus yield different revolutions per the same distance. Therefore, if you calibrate on a very smooth surface (like concrete) and measure on a rough one (gravel or dirt) you will come up w/ an innacurate result.

I'd challenge you to take your wheel to a USATF-certified calibration course and test it there, then use THAT figure to measure a 2 km road loop.

Racewalker,

I agree with most of what you "know". (A XC course could be accurate, though, if there is an adjustable spur or curve.)

Jones counters are only as accurate as the tire (pressure changes) and rider. One of my counters stopped working consistently, but that showed on the calibration course. Counter has been discarded. All USATF courses should be 1 meter per 1,000 meters long. The measurers you have spoken with may not have wanted to get into a discussion about SCPF (short course protection factor) if they told you the 5K course was 5005 meters long.

Most likely cause for incorrect course length (I'm not saying this is the only, nor THE reason, as I am not there to evaluate on-site) is that the Shortest Possible Route (SPR) was not what you measured. If the person that measured the course for certification could legitimately take a shorter route than you chose to measure, your measurement would be long. Apex-to-apex lines and curbless curves are the most likely variables.

whatever you do, do NOT use the method that triathlon directors used in the 1980's, every run i did back then was 15-20 seconds per mile faster than my pace in college,

AFTER a bike and Swim. One course the first two miles were well over a quarter mile short, ridiculous.

[quote]OldXCguy wrote:

My concern was that after the precise measurement of said courses, that there may have been abuses of the SCPF. I believe my uneasiness about the SCPF goes back to when it was first introduced, in the early to mid-1980's. Suddenly, courses in NJ that I had run every year were getting longer, not by a barely perceptible 0.1%, but by as much as 15-30 seconds on a 10K.

In a post on the course measuring forum Pete Reigel points out that prior to 1987 the layout procedure for certifying a course was "young and not fully developed." He shows data that indicates that many certified courses during this era were actually short, and of course before there was any certification many courses were undoubtedly short. You probably did notice a lengthening of courses soon after that, to their true advertised distance.

Another example was a 10K, also within the past month on a course with which I am very familiar. I did a training run on the course and found each mile to be not just a barely noticeable five feet longer than what my Garmin 305 showed. The mile marks were consistently 25-30 meters beyond what I measured. In fact, they were so consistent in their excess length, that I just assumed the SCPF had been applied. At the end, the Garmin read 6.33 (and I cut the tangents pretty tightly). Gmaps gave me the same reading. In both cases, I had maps of the courses available to review.

I guess this is starting to sound like yet another whacky conspiracy theory, but I would appreciate it if anyone familiar with the certification of NJ courses would assure me that they only use the same .001 SCPF that is used everywhere else. Thanks again everyone.

As you know, I also measured the 10k course you're talking about with Google Earth, and as you know, my measurement came out to 9.93-10.00km depending on where you put the start and finish, which aren't easy to locate precisely from satellite images. Certainly close enough that I wouldn't question the certification measurement.

You are making the extraordinary claim that NJ measurers are abusing the SCPF. It's up to you to provide the extraordinary evidence. Export your Gmaps measurement to GPX format(there's a button right there on the page) and email it to me. I'll import it to Google Earth and provide a link here so everyone can take a look at the path you followed to measure the course.

I think some posters are missing the point. It's not that people "believe in the Jones counter." That's like saying "I believe in my steel tape/in my theodolite/in my ****."

The only thing to "believe" about your measuring device is that if you use it correctly, you'll get a measurement that's accurate to within the limits of your device, and repeatable.

The Jones Counter is nothing more than the "readout." It reads out in an arbitrary count that's directly related to the circumference of the bicycle's wheel. My old Jones Counter used to read something like 47,000 counts per mile with the rims and tires I used to use. I have no idea what the newer ones read out, but it's unimportant -- the point is that each "count" represents a very small distance.

It's the PROCEDURE that's crucial!

It's been mentioned but evidently needs to be mentioned again.

1. record what your device "reads out" as the length of a distance THE LENGTH OF WHICH IS KNOWN AND IS TAKEN AS ACCURATE. This is always a straight line, measured by a different "known-to-be-good" measuring device. This "calibrates" your bike, meaning that you know, within tight limits, just how many counts on the Jones Counter will measure a mile (or kilometer), on that day, at that time, in that place.

2. measure the race course, using your just-calibrated counter.

3. return to the course of known length and observe the difference between what your device read out the first time, and what it reads now.

4. adjust

Doubters/complainers -- the whole point is that this is standard practice everywhere in the world of measurement, not just in road race courses. It's true that with many measuring devices (think micrometer, for example, or digital voltmeter) the calibration, once done, won't be redone for some time. With course measurement the recalibration is done immediately. This has nothing to do with the Jones Counter itself -- it's just the readout -- but has to do with the known/expected slight change in the circumference of the bicycle tire.

If you have a digital camera or camcorder and have ever adjusted your "white balance," then in effect you've done a calibration. If you've been around a while and have used an "18% grey card" in b/w photography, you've done the same thing. The standard video "bars and tone" is meant for calibration. Calibration/recalibration is everywhere.

I've measured XC courses and laid out short training distances in parks with a surveying wheel. A surveyor's wheel is a useful tool but it's in a completely different measurement world from the surveyor's other instruments and from a calibrated bicycle measurement. When I got my first wheel, back in the seventies, I immediately calibrated it on the calibration course. It was 9' long per mile and it kept changing as the rubber wore down. This is normal, and expected. It's a property of the tool, and it's not a good enough tool for road race measurement. It may be called a surveyor's wheel but you'll rarely see a surveyor using one. Mostly they are used by construction people -- roads, bridges, etc. -- where it's just the right tool for many measurements.

I love GPS devices. Other posters talk about the positional uncertainty, which can be as small as 10 or 20'. The thing is -- that uncertainty is always changing. If the device is only receiving 2 satellites, then it's high and it can't even attempt altitude. Most modern GPS receivers are 12-channel and when they're receiving signals from half dozen or more satellites the position uncertainty is very low. When the satellites are low in the sky it's high. When they are close together, it's also high. When they are well-placed from an angular point of view, it's low. And so on. My point is that it's always changing because the satellites are in motion and they have different orbits. This isn't a secret.

If you have a hiking-style GPS unit (rather than a wrist one, which doesn't usually display the actual positional data) then take it and put it down somewhere and watch the display that shows your positional uncertainty. It's going to change while you're watching. Switch to the display that shows how many and which satellites are being received -- this is most easily seen on startup, as the receiver tries different channels. You'll see the uncertainty change as more signals are received (or lost), as satellites low on the horizon come in, those high in the sky come in, etc. etc. That's always going on. That's how GPS works.

So, again, measurement people only "believe" in their basic method, which is a standard method, widely used.

Oh, and I should say that of course there are sloppy measurers, measurers make mistakes, and so on. You can put an excellent tool into someone's hands but that doesn't mean that he or she is going to use it properly.