Wheel measurment question

yes but mile markers are exactly the same as the counter on my bike. It reads consistently 4 yards out to every mile marker on a straightish road but with a lot of bends it can be

10/12/15 yards out. I think the 4 yards is cos it's set with no weight on the front wheel, under pressure the tyre is slightly smaller so the diameter is off by a couple of nanoinches.For the bends depends wheter you take them inside or outside hence the error.

For those of you with the time on your hands to become a USATF certifier (OldXCGuy, you certainly read like one to me!), you'll appreciate this partial list of things that lead to differences between 2 measurement rides:

1) Calibrating the bike with your hands on the handlebar drops, but riding the course with your hands elsewhere on the handlebar.

2) A change in temperature of the bike tire.

3) Dry calibration course, wet road race course.

4) One measurer rides 13.1 miles for half marathon, the other rides the correct distance (13.109375 miles / 21.0975 km + SCPF).

5) One measurer rides 3.1 miles for 5K, the other rides the correct distance (3.10685591 miles + SCPF).

6) One measurer rides 6.2 miles for 10K, the other rides the correct distance (6.213711928 miles + SCPF).

7) One measurer rides a curve within 12 inches of the inside track, the other rides the curve within 15 inches of the inside track.

8) One measurement ride is up the hill, the other is down the hill.

9) One measurer stops to move their bike around parked cars, the other rides their bike around the cars without stopping.

10) One measurer uses only the rear brake to stop, the other uses the front brake.

11) One measurer assumes runners will stay on the road at all times, the other knows that runners will seek the shortest path, even if that means going onto a sidewalk at times.

Many years ago, I road a course with a person who had some experience measuring courses. The course included a number of long, curving sections. At the end of 5 miles, we were over 100 feet apart. Measuring requires careful, repeatably precise riding skills.

How many of the differences mentioned above will be detected by using a GPS? You have to understand the principles of measurement, and the need for verifiability by someone else who is going to check your work.

Bottom line: If the course ain't certified, you're doing a FUN RUN! Make sure you're not paying too much for them!

How long does it take to accurately measure a course? Say a 10k? And how much do the measurers get paid? Just expenses, I'd assume.

Ride calibration course 4times 15min

drive to course

ride 10k twice 90-120min

calculate and correct distance and make adjustments

drive or ride course and paint/mark splits 30min

Drive home and ride calibration course again 4 times

Complete application for certification and detailed

map 2-4hrs.

I charge a flat rate of $200 for 5K, so 10K=$400 this is good for 10 YEARS. Regional prices vary I am sure.

Another measurer - great reply

interesting... wrote:

How long does it take to accurately measure a course? Say a 10k? And how much do the measurers get paid? Just expenses, I'd assume.

Since I'm waiting for the rain to clear before heading out for a ride, I'll try your question on.

You don't specify what you mean by 'accurately measure a course'. My road bike measures very accurately and I could lay out many a course w/it and feel comfortable w/the distance. Or, I could use a surveyors measuring wheel and get a pretty good read on a course. However, if you're after accuracy at its best, the certified course method is what you want. Then I'd haul out my 24 year old Trek w/a Jones counter on it to measure.

The answer to how long it takes to measure varies quite a bit. On my road bike w/the little computer, it'd take about 45 minutes to measure & mark a 10 km...a surveyors measuring wheel would take at least 4 times as long; both assume the course allowed for distance to be added on since 99% are originally laid out short.

Certifying a 10 km takes me about 2 hours. This does not factor in travel time, calibration time or trying to figure out how & where to add distance, if needed (which it invariably is). I have also not factored in how long it takes to draw the map for the letter of certification.

What I would charge would depend on what level of accuracy you're after.

I've noticed people mentioning mapping software such as google earth. I have to guess that this would be much less accurate than most people would hope. This type of software maps a 2-d picture of a small section the earth onto a grid of GPS coordinates. Remember the round-earth/flat-map problem from geography class? The software attempts to map a 2-d picture of 3-d terrain onto a 3-d set of GPS coordinates. Also, many of the satellite pictures used were not taken from directly above the target (if you zoom in on buildings from various cities, you will notice this), so the algorithms used also have to adjust for perspective. My guess from looking at certain familiar areas is that you will get local distortions in the pictures in order to make them fit with the GPS coordinates at certain calibration points, not to mention the fact that the GPS coordinates have their own sources of error. I doubt the individual pixels match up with the coordinates within the accuracy needed for an accurate course measurement.

Another Measurer, thanks for your thoughtful, carefully considered reply. Since tone of voice does not come through here, I want to say that I mean that sincerely, with no sarcasm intended. (Was that a compliment in the first sentence? I'm not sure.) I don't quite follow your argument, though. First you list eleven ways where course measurers can vary, then you conclude that course certification is a precise process.

Anyway, let me first admit that I do not own a Jones counter, and I'm not even sure what one looks like. (Actually, I think you could legitimately label me a weirdo if I owned one and went around checking courses with it, without being a certifier.) So does that preclude me from forming reasonable opinions about course accuracy? I say no, based on many years of observation (almost thirty), and measurements wtih two different devices. And by the way, I notice that people throw out the term "GPS device," assuming that all are the same.

My Garmin 305 seems much more accurate (based on reproducibility, coincidence with mapping sites, etc.) than my previous 201, and many other people have found the same.

Secondly, I never said that GPS measurements are more accurate than a Jones counter. I'm saying that since I don't own a Jones counter, I'm left with available measuring devices, as noted above. I am not at all being critical of measurement techniques used by course certifiers. My complaint is that it seems that after all the precise measurement is complete, and an accurate course is obtained, some certifiers in NJ add in an overly enthusiastic SCPF, to ensure that runners travel "at least" (and I've heard them say that) the stated distance.

As an example, at the 5K I alluded to earlier that I believe was .04 miles (not sure how many meters that is) long, my 305 coincided precisely with the first two mile markers, I mean to within a step. Then the last 1.11 mile came out to 1.15, both on my Garmin and on Gmaps. Did both

measuring devices suddenly go haywire at that point? Seems unlikely.

Lastly, I have NEVER gone up to a race director and told him or her that a course was short based on my Garmin. I wait until I get home to re-measure on Gmaps. ;-) (Just kidding, just kidding.)

Ultimately, this is an argument I can't win. Even if I manage to convince everyone that those courses were off, you would say, "Oh well, those are just a couple of isolated instances."

Slow day at work, so i did a bit of looking around online. THis is pretty interesting:

http://www.cage.curtin.edu.au/%7Egordonsj/course/

Some professional surveyors tested the Jones counter method and found it to be very good (in terms of repeatability and accuracy) and that the "short course prevention factor" of 1 part in 1000 is reasonable.

I also appreciate the reasoning behind putting ensuring that a course is NOT SHORT as the top priority, because you don't want the world record for the marathon set on a 26.1 mile course. So if the error on a measurement is 0.1% then you should add 0.1% to the length of the course to make sure it's at least the stated distance.

All the calibration proceedure & that seems reasonable (from what I remember of college physics experients) so yeah, big up to the measuring guys.

Guess i was just curious as to how much work's involved and whether it's something you can make a living out of, a source of beer money or just because you want to help the sport!

It is usually shoe money for me. I think it would be hard to have enough business to make much more.

OldXCGuy, you seem to have the passion for race course accuracy that drives many of us that measure courses for certification/record validation purposes. It's quite frustrating to see someone run a 'record' or 'personal best' on a course that later turns out to be quite short, whether due to incorrect measurement, mismarked arrows, mismarked start and/or finish line, moved or missing safety cones, faulty navigation by a lead cyclist/car, etc.

If you have decent bike riding skills and the experience in running courses that's needed to identify the shortest path during a measurement ride, you can and should become a measurer also! This will also help you to scientifically explore your curiousity about how accurate your GPS devices are (you may be interested to know that two different GPS devices, worn by 2 different runners, will likely get different measurements for course length as well). Heck, if GPS manufacturers were really touting accuracy, they'd have a mode that would show distance to the .00001 of a mile, right? Forget that .01 crap, that's 52.8 feet!

You need a device AND a measuring method that is sensitive to small differences - think inches. That's what we use. If our two separate measurement rides are too far apart, we have a problem. However, remember that we start with a system the reliably measures distances to about 4 inches per 1/4 mile (and some use a system that measures to about 1 inch per 1/4 mile), so if our rides measured too far apart, we have confidence that there is a problem somewhere, and we have a way to find it and correct it.

Those of us who measure courses for accuracy want overly short/long courses identified and corrected. You make a case for having found one in NJ - take the next step. Get the map of the course, and compare the route traveled by the runners to the route specified on the map. Was the finish that day at the wrong location? (for example, the map may state that the finish is 112 feet, 4 inches north of the northern edge of a sewer grate on the east side of the road, but someone measured 112 feet, 4 inches south from the sewer grate on the west side of the road because they hadn't had their coffee yet) Was the 3 mile mark at the correct location? Did someone misinterpret a paint mark from something unrelated to the race as the finish line paint mark? Even if a course is certified, mistakes can happen. We'd like to find ways to avoid those mistakes, too. This is not a 6-Sigma process.

If the first 2 miles agreed with your GPS, then the SCPF would not be at issue, since it applies to the ENTIRE course measurement, not just the end. For example, the mile mark should have been about 5.28 feet after what your GPS recorded, the 2 mile mark should have been about 10.56 feet after what your GPS recorded, and the 3 mile mark should have been about 15.84 feet after what your GPS recorded. I suspect the finish was just mismarked.

In the early part of the pose, you seem to be confusing precision with absolute precision. Just because two different bike rides don't agree to the inch doesn't mean that a course is not accurate enough for certification/record validation purposes, or that the method and technology used is not precise enough for same.

For example, when I measure a 10K course, the 2 rides are typically within just a few feet of each other. That means, over the course of the 6+ miles, the measurements were within 1-2 walking steps! Some of the 11 items I mentioned may be involved, or others may be involved. Or, when I recalibrate the bike after the measurement, I may find that the two are actually closer than I thought because of the temperature differences in the bike tire. Usually, all I have to do is determine which of the 2 measurement rides is shorter and, if needed, extend the course a few feet with a steel tape. I've even measured courses where the 2 rides were within 8 inches of each other!

Again, you read like you have the passion and experience needed to measure courses for certification purposes. If you have precise bike handling skills as well, I hope you join us!

It may not be the measurer at all, but the race director deciding that the finish line is more convenient at location "x" and figuring no one would notice. You may want to pull down the map from USATF.ORG and see if the course you ran is the course as measured. In any case, you can do a simple double check without a Jones counter. If you have a bike with a reasonable odometer you can calibrate it on a straight section of road of a known distance. Measure it with a tape or wheel, ride it 4 times and figure out how close your odometer is. Not USATF quality, but I use that method some time for layout rides.

Or both use a similar algorithm, since both are waypoint based it's not surprising. Is there a difference is terrain, turns, etc, in the last mile? It's also possible that curbs, etc, were added since the course was measured that changed the tangent. Sounds trivial, but I had a course where they added some center islands and it added good 150-200 feet to the course. Changed a block long diagonal through a wide intersection into a block straight and a near right angle turn.

If you had, you wouldn't have been the first.

If by "win" you mean that measurers would admit your Garmin 305 is an accurate measuring device for validating course distance, I'd say you're correct. Same with Google Maps (or Streets and Trips, etc). Being a gadget geek I've used all manner of things to try to make my measuring job easier.

David and others:

I am looking to become a "USATF listed" course measurer. I have read the USATF course measurement manual and am in the process of purchasing gear. Can you recommend good brands/models, for example, for a 100 meter steel tape?

A little background: measurement is my profession (electrical engineering professor) but we don't use steel tapes for our measurements! I've talked with a bunch of profs in our Civil/Surveying group about a few things, and of course their needs are a bit different than ours. The exchange has been enlightening on both sides though!

I do have one possible answer regarding the the fact that GPS-measured courses (the wrist watch style) always seem to give a distance longer than reality. Many people are not aware that a GPS "measurement point" is really a circle, indicating the probability of the true location. In simpler terms, any given measurement point may be off from "true" by several meters. Now consider what happens if you walk a perfectly straight line for, say, 1000 meters. The GPS unit is recording measurement points as you walk, but each point has a built-in error. If you joined these point-to-point, you wouldn't get a straight line, you get a zig-zag around the straight line. Even if you did a simple second-order curve fit to average it, the path would be more like a drunkard's path, and thus, wind up over the "shortest possible path" distance.

Jim, I don't know where you can get a 100 meter steel tape. Even if you found one, it might prove cumbersome to use. I use a 100' steel tape, off the hardware store shelf. It's been compared w/others and is 100'. If you're not sure of brands, get the most expensive and/or see if the store will let you compare tape lengths before purchase. You mention you have surveyor friends...see if you can talk them into surveying a cal course for you for beer & pretzels. Otherwise, use your hardware store 100' steel tape.

100 meter tapes aren't that hard to find (they're reel types, not the pocket carpenter kind). Interesting that one of my surveyor buddies said the expansion coefficient for a nylon clad tape is different from straight steel, although the USATF manual says you can use either.

The road in front of my house is straight and not well traveled (but good asphalt). I figure I can make a 500 meter cal course on it with little trouble (probably not 500 precisely as I'd use a solid landmark such as a post for the endpoint).

If I was a real nut case I'd get an EDM (I saw one for $1k that's accurate to +/- 3mm over 200 meters), but my pockets aren't that deep.

Keith Stone wrote:

I used to ride with a handlebar mounted Garmin GPS when I was measuring. It wasn't one of the el-cheapo $150 units either. I liked to have waypoints for the mile markers. While is was great at getting you exactly to point "x", it sucked at measuring the distance you covered to get there. It was consistently off +/- 5%.

I have performed and documented 9 rides so far with a calibrated Jones counter and a Garmin 60csx both mounted on my bike. On 3 of those rides I also wore a Garmin Forerunner 205. I also ran one of the routes wearing the Forerunner. In none of those cases did the GPS measurement differ from the Jones measurement by more than 0.4%. In 7 cases the difference was less than 0.1%, or 1 meter/km. Keith, I think your GPS must be an old model.

Jim Fiore wrote:

In simpler terms, any given measurement point may be off from "true" by several meters. Now consider what happens if you walk a perfectly straight line for, say, 1000 meters. The GPS unit is recording measurement points as you walk, but each point has a built-in error. If you joined these point-to-point, you wouldn't get a straight line, you get a zig-zag around the straight line. Even if you did a simple second-order curve fit to average it, the path would be more like a drunkard's path, and thus, wind up over the "shortest possible path" distance.

When someone runs, 95% of the time they are going in a straight line or a very gradual curve. When the GPS device sees any kind of zig-zag path, I'm sure it ignores the zig-zags and fits the path to a straight line or gentle curve when calculating distance. Besides, when I download tracks from my 60csx, I don't see much zig-zagging anyway. I think the reason is that most of the GPS error is bias error(same for all tracking points) with only a small component of random error. The bias error would have no effect on the distance calculation.

Jim Fiore wrote:

Can you recommend good brands/models, for example, for a 100 meter steel tape?

Here's the one I bought (www.onlinesports.com search for item SKH-TST30). After much trouble with the winding reel that it came with, I disconnected the tape from it and now store the tape on a wheel that is normally used to store/wind/unwind an extension cord. It works great.

Right now a new version of the Jones Counter is being developed, and should be in production by the year's end (the parts for the older style are no longer available). There is a current version floating around but people have reported problems w/ it (some have to mount it backwards on their bike wheel, etc.) I'd wait until the new one comes out.

Right now a new version of the Jones Counter is being developed, and should be in production by the year's end (the parts for the older style are no longer available). There is a current version floating around but people have reported problems w/ it (some have to mount it backwards on their bike wheel, etc.) I'd wait until the new one comes out.

dukerdog wrote:I have performed and documented 9 rides so far with a calibrated Jones counter and a Garmin 60csx both mounted on my bike. On 3 of those rides I also wore a Garmin Forerunner 205. I also ran one of the routes wearing the Forerunner. In none of those cases did the GPS measurement differ from the Jones measurement by more than 0.4%. In 7 cases the difference was less than 0.1%, or 1 meter/km. Keith, I think your GPS must be an old model.

My personal GPS isn't the newest, but it was built well past the degradation of the signals and actually works well in open territory. It works on the calibration courses, and on the course I had to do for a charity run that was two loops around a shopping center parking lot, but in trees and buildings and hills and turns it's not so hot. Unfortunately that's most of the courses around here. Maybe the newer one's are better, but the emails I get make me believe otherwise.

As far as the ForeRunner 205 that's the exact model one of the local runners who declares all the measurements inaccurate wears. She's the type that in order to log 8 miles she loops the track at the end of a run if her Garmin says 7.8 miles. Needless to say she has provided reams of documentation of all the mistakes I and other regional measurers have made. When a stretch of road or loop of a park has been measured by multiple people and bikes and had the same result and you have various Garmin wearers claim you're both long and short I tend to go with the bike.

I still have a guy that claims a half marathon I did is 14 miles because that's what he came up with in Gmaps. You can find his version if you search on Mistletoe and NC. Zoom in, pick satalite and you'll see the problem right off.

I have no doubt there are courses where errors were made, changes have happened to the tangent line that voided the original measurement, or the course as ran doesn't match the course as measured. I just don't buy that GPS or GMaps is a reliable way to prove that inaccuracy.

I really want it to be true, since as a gadget guy I had hopes of riding a course with a GPS and coming home and auto-generating my course map complete with mile markers. I paid good money for the whole Garmin schtick, software and all. Look up my maps, you'll notice I didn't use the Garmin software for any of them.