Calibration Course

How did / do you judge pull tension at the far end?

A small, portable "fish scale" works. Then when you learn what a "Newton" feels like pulling the tape with the scale attached, it becomes easy to pull it just as hard or harder than required just by feel.

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.

You're a better engineer than I, Oscar. Aren't most steel tapes equipped with a loop end? Just hook your DE-LIAR onto this loop, pull, and mark your tape appropriately.

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.

Oscar

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.

Linear - had not considered that.  Just points out the dangers of not knowing the answer before you take the test!  But it does say something about range of observational variations being hunched over on your knees on lumpy (1/8" aggregate poking up) masking tape while trying to hold tension.

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.

Over 20 years ago, I questioned Carl Agriesti (last measured course shown has a 1983 cert date) about a cal course that started flat and ended up halfway up a hill.  His answer was that you are calibrating the rider as much as the bike.

I've also been wondering about the length of cal courses. I have scoured my community and find few places to set up a decent 1000-foot cal course.

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.

https://measure.infopop.cc/top...-calibration-courses

https://measure.infopop.cc/top...s-unnecessarily-long

https://measure.infopop.cc/top...ation-over-25-meters

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.

Considering most of us wobble a bit when we begin a road course measurement, wouldn't this tend to simply replicate or approximate that which we experience during a calibration ride?

No, because you don't stop and restart every 300 meters when you ride the race course.

I took a measurement seminar from Pete Riegel in 1996 and do remember him saying that we needn't worry about a bit of wobble as it doesn't make much difference.

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.