In view of the many advantages of pressure monitoring that make the measuring process simpler and more accurate, I am surprised that in over a year there has been virtually no interest in the method.
Pete Riegel did extensive testing and confirmed my findings remarkably closely. Unfortunately in the middle of his first course measurement he went over rough ground and some teeth in the gearing of the pressure gauge jumped position. Although this did not spoil his measurement and in fact the gauge is still usable (albeit with a displaced zero), no doubt this confirmed his preconceived notion that the gauge was not in the least rugged enough to withstand being mounted on a moving wheel.
To the contrary, I now wish to report I have used the very same specimen in Presta version for over 50 certifications through 600 miles (some of which were rough) and the gauge is still going strong. In fact I have recently found it gives identical readings to that of a brand-new specimen within readability (2 kPa, 0.3 psi). My check was to repeatedly exchange gauges on a stem. (No air loss was detected between exchanges.)
After I reported detailed instructions for construction of the gauges, Justin Kuo used the telephone number I gave to get the parts from the Gauge Distribution Co. Unfortunately he was turned away with the response that they were having difficulty in filling special orders anymore. I have tried the number repeatedly since, but could never get an answer. The on-line site (GetAGuage.com) is not set up for special orders, but I took a chance and requested 4 gauges using the contact email address with the following specification:
K160X, Accu-Gage, 1.5-inch diam, 160 psi, with straight chuck and no epoxy glue
A week later the gauges arrived with a total charge of $41.45 to my credit card.
I always calibrate on the day of course measurement, but I have evidence that the calibration is valid for quite a few days despite temperature changes and loss by diffusion. For instance four days after measuring a course in downtown Raleigh, I met with the race director downtown. Returning to my car on my measuring bicycle, I thought it would be interesting on the ride to remeasure the first mile of the course. Calibration four days earlier had shown 771.13 rev/ml at 602 kPa. In the meantime pressure had dropped mainly by diffusion to 570 kPa. My calculator program indicated 771.81 rev/ml but this uses a modified pressure coefficient for the case where measurement takes place a few hours after calibration and pressure change is brought about mostly by temperature change. It seemed more appropriate to use the regular pressure coefficient, since air loss was a major factor:
- 1 rev/km/bar = - 1.6093 rev/ml/bar = - 0.016093 rev/ml/kPa
Thus new calibration factor = (570 – 602) x (-0.016093) + 771.13 = 771.65 rev/ml
My ride found the mark placed four days earlier at 771.51 rev , which is only 0.018% different from that calculated above.
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