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After 40 years of measuring I finally set up a calibration course by myself today.
I had to measure a marathon & half about a two hour drive from my home and no one willing to make the trip. Pete had come up with a method but I decided to re-invent the wheel (didn't research what he did).

1.Screwed an eyelet into the end of a plank of wood approximately 4' x 8" x 1"

2. Placed the wood on the ground with the end about 6 inches from the start of the calibration course.

3. Drove one of the tires onto the blank.

4. Using a plastic tie, attached the end of the tape to the eyelet.

5. Place a piece of white tape (vinyl) under the end of the tape. Pulled the tape and marked the zero point.

6. Rolled out the tape, pulled, and marked the 100 meter point.

7. Rolled back the tape and checked that the zero point had not moved - it didn't. Cut the plastic tie, packed up and drove down to the 100 meter point.

8. Repeated the process with a new plastic tie. This allowed me to adjust the distance of the eyelet to the new zero point. I thought about leaving the tape attached to the eyelet when transporting but I thought the wood would shift a little when I drove up on it.

One snag: I was setting this up about 2 feet from a curb on a nice straight road. At the end of the first 100m segment there were leaves on the ground and it was too damp to hold the vinyl tape. Used my little retractable 12 foot tape and placed marks 4 feet from the curb (beyond all the leaves) every 5 meters along the entire 300m calibration course. Started from scratch.
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Very innovative technique, David. I like the solid anchor idea.

If you don't mind doing some math, you could leave the zip tie attached to the eyelet. And, if you have a two-sided tape (ie. one side with metric units and the other with imperial units), you can get the two required measurements in one pass. (I borrowed part of this method from Pete.)

The process would go something like this.
  • place a piece of vinyl tape onto the road and mark the starting point.

  • position the tape so the first mark is somewhere between 0 and 1 meter. Record that value. (If you have a two sided tape, flip the tape over and record the mark on the reverse side.)

  • pull the tape to between 99 and 100 meters and mark the point on a second piece of vinyl tape. Record that value. (If you have a two sided tape, flip the tape over and record that mark.)

  • calculate the metric distance. (If you have a two sided tape, calculate the imperial distance.)

Repeat until you have your approximate distance. Calculate the average distances from the two sides of the tape and then do the temperature adjustments.

That it. -- Justin
Justin, maybe I am missing something in your description. But, I don't see how using a double-sided tape satisfies the 2-measurement process.

If you mis-anchor for one pass, say 1 foot short, both sides of the tape will still show you have enough length. So, you may measure what you think is 1,000', or 304.8 meters, but it is actually 999' or 304.45 meters. Appears that you have measured correctly, but without pulling the tape a second pass, you may make a mistake.

Same concept as me using both an electronic counter and a Jones counter at the same time, and riding a course once. Both counters say I rode the right distance, but if I made a wrong turn, or swung too wide, or cut a corner, it won't show - my course would be wrong.
I've been intrigued by this question about a one-person layout also. I did it once, and I think I essentially did a version of Pete's method. At the recent seminar organized by Mike W and company, I asked Pete about a demo of that, but we didn't have time for it as it turned out.

My question for Dave: what did you have to pull against, and was the system strong enough? (sounds like you pulled against the vinyl tape?)

I have the same reservation as Duane about counting that (Justin's method) as two measurements-- it's just one measurement in two languages I think.

I usually manage to con the race director into helping me lay out a cal course when I need it. One advantage of that is that it pulls them into the whole world of striving for accuracy, and they usually feel good to be part of the process.
A few years ago there was a guy who posted who built a big sled out of 2x4s and cinder blocks to use as an anchor. People pointed out that transporting the thing to measurement locations might be an issue. But David has solved that problem by using the transporter as the anchor!

I still think you missed a great photo-op though, of looking down the length of the tape just as you are preparing to make your mark, and seeing the vehicle holding the tape at the other end.

After this posting I am now anticipating getting a calibration course application from some measurer with the second name on the steel tape data sheet listed as "Chevrolet Silverado."
Originally posted by Duane Russell:
If you mis-anchor for one pass, say 1 foot short, both sides of the tape will still show you have enough length. So, you may measure what you think is 1,000', or 304.8 meters, but it is actually 999' or 304.45 meters. Appears that you have measured correctly, but without pulling the tape a second pass, you may make a mistake.

Duane, You are absolutely correct. Reading the tape on the metric and imperial sides may help catch errors in reading the tape. It won't catch errors due an end moving or slipping from the tire, or if the vinyl tape moved. Measuring forward and then repeating by measuring backward will help catch most of the tape measurement errors. -- Justin

But how do you hold the other end where there is nothing but nylon clad steel tape to grab onto?  After I asked the question I tried this and it seems to work OK at up to 24 pounds of pull. Cut 2 pieces of 1 1/4" flat stock (one 1 3/4" long and the other 3 " long). Bolt them together with 3/16" machine screws and nuts.  Drill a 3/8" hole at the far end of the 3" piece.   Lot of other better materials but that is what I had.


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OK, I pulled the reel cover plate and there is a loop of pure tape but to make that loop the tape necked down to about half.   Pretty sure though that the loop would deform plastically with a direct hook up to the thin metal De-Liar hook.   You could pretty easily rig up a clevis arrangement though and use the loop.  I have been "calibrating" my hand with a 20 pound weight just before measuring and directly pulling on the tape.

This is a gizmo to make tape pulling with a DeLiar convenient.

Then, tried an experiment.: The “zero” end of a 200’ CST Berger 82-20010 B tape was nailed to the pavement of a walking trail. Then the tape was stretched out 200’ and allowed to relax.  An alcohol thermometer was set out in the shade of the tool.  Then a piece of masking tape was marked with a line at the 200.000’ point of the tape.  First, the tape was stretched using one hand “calibrated feel” tightness and a dot was put on the tape at that point.  It was awkward both holding the tape with one hand and marking with the other.   Next, pull forces of 5, 10, 15, 20 and 25 pounds were applied using the De-Liar which is over 50 years old.  A dot was made at each point.  A temperature of 83 F was noted at about 8:05 pm.

A passer-by asked if I needed any help so the experiment was repeated but this time two hand pulling was possible.  A second piece of tape was put down right next to the first tape and the 200’ point marked.  It was noted that the 200’ relaxed point was not even .005’ past the first set of measurements.  I pulled and she marked the particular pull points.

This is a table of results:

A few days later, I tested the 50 year old Deliar against a 20 lb dumbell and got only 18.5 lb.  That means 20.0 lb indicated was really 21.5 lb applied.  AND that the calibrated hand applying 20 lb force was almost dead on what it should have been.



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Pete Riegel is smiling from above to see someone conducting and reporting on experiments in this forum. Thanks Oscar.

Like most people I'm guessing, I tension the tape by feel when measuring a cal course. I do occasionally get my fish scale out to check what 10-11lbf feels like though, just as kind of an ad-hoc calibration. I think there is a tendency to pull harder that you should, so it's a good idea to check yourself every now and then.

The stretch of the tape should be linear as a function of pull force. The fact that your data does not show this just indicates it's hard to be precise with this, and there is going to be some scatter. The hope, which I think is justified, is that the scatter of multiple tape pulls will tend to cancel itself out.

Been thinking about cal course distances lately and I was wondering if longer cal courses are inherently problematic.  It seems to me that the longer a cal course, the more room for error, whether it be tire wobble or not being able to ride the course perfectly straight, or error in setting up the cal course itself, etc.

In my opinion, the most accurate calibration would be 1 count of a Jones counter.  Although not practical, if one could measure the distance a tire traveled for 1 count and extrapolate that data to arrive at a constant, that would provide the most accurate calibration data.  So, if my theory is correct, wouldn't shorter calibration courses provide more accurate constants?  To me it seems that if a measurer has a 100 foot steel tape and lays out a cal course with that, he/she will have less chance of making an error if there is only a single layout of the tape.  Multiple layouts of tape (to achieve a 1000' course) are multiple points of potential error.  I know there are safeguards in place but a single layout would eliminate the need for those safeguards. 

I think that removing potential error points makes for more accurate courses.  As far as I can surmise, every extra tape layout, every extra millimeter traveled on a cal course has the potential to affect course (both calibration and race) distance.  Not sure if 100' would be the right distance but I do think that cal courses should be less than 1000'.  Maybe make 264', 352' or 528' the recommended distance?

I'm probably not the first person to broach this subject but I didn't see anything about it on the forum and I wonder what others that have been doing this a lot longer than me think.

The theory is that the biggest source of error in riding calibration courses is the inevitable "wobble" at the beginning of the ride. It's very difficult to ride perfectly straight when you are first start from a standstill. With a very short calibration course this wobble error will make a big difference in the overall calibration count. For longer calibration courses it will make less difference.

When I measured a track with a measuring wheel, I calibrated the wheel with a 100-meter calibration course, because I reasoned there was no "wobble" at the startup. A 20-meter calibration course probably would have worked just as well.

Over the years several people have questioned the 300-meter required length of calibration courses, pointing out the fact as you have, that there are other sources of error that will be bigger for long calibration courses than for short ones. Having to use multiple tape lengths is one, however I tend to think that the small allowable tolerance between the two measurements of the course helps with that one. For me, the more concerning error source is the fact that in some parts of the country it is difficult to find a good location for a 300m calibration course. So people end up locating their course in a location with a slight hill, or where the road isn't perfectly straight, or where the surface isn't typical (concrete instead of asphalt). If they could set up a 100m or 200m cal course they could probably find a better location.

Is the error caused by the above issues bigger or smaller than that caused by startup "wobble?" That's the question.

Here are some threads from years past addressing this issue.

I also had a thread reporting results of an experiment I did with 3 different cal courses (100m, 200m, 300m) in the same location. I did multiple rides of each one and compared the cal constants. Unfortunately, I can't find that thread.

Obviously, you haven't measured in downtown Baltimore without police escorts, Mark .

Actually, I recently re-measured part of the Baltimore Marathon to accommodate a new course configuration requirement. For the first time for several measurements, the City provided me with 4 "motors" and one cruiser. A large portion of the downtown area was briefly closed to traffic as I measured there. These police escorts did a fabulous job. I was able to get through the 11-mile section in a fraction of the time it took when I measured here with no escort.

I agree with Pete and Paul. Unless our wobble is somehow more than the expected slight back-and-forth of our front wheel at the start of pedaling, it seems to me this should make little difference.

Last edited by Race Resources LLC

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