Skip to main content

I have laid out my first calibration course using a 100' steel tape. The tape did not have meter markings. I measured 1640' and when I did my first ride I got 516.3 clicks (I'm assuming meters on the Jones). The four rides averaged 516.5. This seems like a large difference to me. If I use this constant times the SCPF I get 517. I took this to mean I would multiply 10000 meters by 1.034 (517/500) yielding a course of 10340 clicks. Does all this sound reasonable and is the difference just related to the size of the wheel? Thanks for your help!
Original Post

Replies sorted oldest to newest

Mike, even though you measured the calibration course with a 100' tape, you should get everything into meters as soon as possible. Your 1640 feet is equal to 499.872 meters (there are 30.48 cm per foot). This gives a count of 516.5/499.872 = 1.03326 counts per m. With the SCPF that becomes 1.03429 counts/m. That is way too low. Usually the counts are about 10 per meter.

Also, I don't understand you statement "I'm assuming meters on the Jones".

Maybe I'm missing something.

I assumed the Jones counter measures in meters. That is, if you had the right diameter tire, you would hit 500 clicks for 500 meters. My calibration course is 1640' 5.03" which should be exactly 500 meters. Your statement "Usually the counts are 10 per meter" agrees with what I was saying about the Jones counter, I just didn't express myself very clearly. We're just a decimal point off. I was sort of looking at the right most counter as a tenth of a click. I know it will take me a little while to become conversant in the language of course certifiers!

Here is what I hope will be some helpful corrections and advice.

First, your counter does not read in meters, or in feet, or in any other unit of length. Because of its gearing it records 23.636363…. COUNTS for every revolution of the bicycle wheel.

When you read your counter, the average reading was not 516.5 counts over the 1640 feet. It was 5165. I hope this is exact. It is a mistake to round off the number prematurely.

Your riding constant over the measured 1640 feet (499.872 meters or 0.310606 miles) will thus be: 5165 counts / 499.872 meters = 10.3326 counts per meter. For USATF road measuring the short course prevention factor of 1.001 must be applied, and the 10.3326 is increased to 10.3326*1.001=10.3430 counts per meter.

So, if you want to lay out a 10 km course you will need to ride 10000*10.3430 = 103430 COUNTS.

Since a mile has a length of 1609.344 meters, each mile you lay out will require 1609.344*10.3430=16645 counts.
Thanks for the help. I think I have the exacting and unyielding approach needed to be a certifier. For example: The tire on the bike I used has a diameter of 27.5". If it had been 28.44" it would have yielded exactly 5000 counts on a 500 meter course. I used a course measuring 1640' 5.03" and used a count of 103422 per 10K.
Thanks for providing such a complete certification manual. It made this process as clear as is humanly possible.


Add Reply

Link copied to your clipboard.