What's the Speed Limit?

Are you asking people if they think their ability to ride the SPR changes with different speeds, or are asking if they think their bikes measure differently at different speeds?

Tom,

Speed was probable the factor. You may recall the OT measurement where one of the riders went over the 15mph and found the course to be short. Since the other 4 riders found the course to be accurate, we found that going too fast can cause problems.

His first thought was the problem was with the Counter. That the Jones simply did not record correctly at higher speed. And the "Speed Limit"
was imposed because of this. The measurer is a good cyclist and probably does better at speed than the rest of us.

I have to agree with Gene. When I left my counter on all the time, even for training rides, I mangled some of the inner teeth. I don't ride that fast, any more, so much over 15 mph has a good chance of harming the Jones Counter. The skipped counts only occurred at speeds over 15, as my calibration rides all were within a click of each other. Speed can introduce inconsistency.

I now take the counter off when I am training, and keep my speed at 15 mph or below while measuring. It only adds a few minutes to a half-marathon measurement, so to me, it is not worth the risk of mangling the gears.

There's a post thread from October 2011 where Jones counter expert extraordinaire Pete Riegel explains that the "skip" is probably due to a broken tooth. I don't understand how the "skip" goes away by reducing speed, once a tooth is broken.
I think I have a JR counter with a broken tooth. The 2nd wheel (10's) stopped completely. I'll disassemble, photograph and post.

Speed is not alone in affecting accuracy and/or repeatability of measurements.

Over the last thirty years a lot of work has been done in an attempt to find out what makes measurements of the same thing differ.
There are two main causes of measurement difference. They are:

1) Failure to ride the same path, and,
2) Variation in the size of the wheel.

We can argue until the cows come home about how best to account for cause (1).
Cause 2 can best be addressed by using straight-line measurements in the methodology.

The past issues of Measurement News contain many studies of measurement difference.
The best way to find them is:

1) Go to www.rrtc.net
2) Click on “Historical Archive on RunScore.com”
3) Click on Measurement News
4) You will find an index of all articles.

You can search for “calibration” using this list. Or, if you wish, you can copy the index to Excel and search it more easily.

Causes for change in wheel size include:

1) More or less force on the wheel
a. Change in rider posture
b. Wind
c. Inclination of the road surface (uphill vs downhill)
2) Change in size of the wheel
a. Pressure loss by leakage
b. Pressure gain by temperature change

There’s more but I am about out of gas. Check out the historical archive. You’ll find a lot of thought-provoking stuff.

In addition to the source of info on this topic that Pete posted, there are many threads on this bulletin board discussing the same topic. The easiest way to find those is to go to the list of interesting topics
http://www.dukerdog.com/USATF/...tin_Board/index.html

and check out the first topic, calibration courses.

One way the counter can skip at higher speed, but not a lower speed, would be that there is enough slack in the counter that the teeth may not mesh perfectly each time. Thus, with higher speed, a tooth may skip its groove for one number.

Do this a few times, and the tooth may soften, or be worn to a "hangnail", instead of a solid tooth. The hangnail is sturdy enough to move the counter at slower speeds, but not at high speeds.

When I took my malfunctioning counter apart, that is what I saw - a disfigured tooth that still had enough bulk to move the gear at low speed, but not consistently at higher speeds.

Like.