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I hope to make a full report soon on my investigations into the pressure-monitoring method for improved efficiency and accuracy in course measurement. However, on 8/5/05 during the certification of “Run for Life” in Raleigh, NC, I tested a pressure gauge I devised for the continuous monitoring of tire pressure, and results were so good that I feel measurers should learn about it without delay.
The gauge can be assembled quickly from currently available parts for about $12, It is screwed onto a Presta stem just enough to register tire pressure and can remain in place for instant readout during bicycle rides as shown in the photo. (A rim with Schraeder hole can be converted to a Presta hole with an adapter costing only a few cents.) The gauge is so light that it has no detectable effect on the handling of even high-performance rims. It should appeal to those traditionalists who believe that it is sacrilegious to even think of adjusting tire pressure, because many of the advantages of pressure monitoring can be enjoyed without having to do so.
For simplicity I decided that I would not adjust pressure during course measurement unless pressure readings indicated it would be necessary to avoid a short course. In fact adjustment was not necessary despite the fact that a thunderstorm occurred in the middle of measurements that dropped the temperature by 15 deg C within a few minutes.
Performance of the gauge was flawless throughout measurements. Of course in the pressure-monitoring method postcalibration is not relevant, but I did one all the same for the purpose of method validation. A table of results and notes are at the following address:
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This subject has laid idle for a while. One question that's not clear to me - does the method depend in any way on past performance of the tire, or is it self-contained within any given day?

If I buy a new tire and pressure gauge, can I use the method on the very first day? How?

Say I calibrate, and my pressure is 800 kPa. I begin to measure at 790 kPa. When I am done my pressure is 810 kPa. How do I know far I have gone?
Pete and Matthew:
Since I made the above posts I have obtained some very nice results, but unfortunately my assumption of responsibilities as a validator has delayed my issuing a full report.

I will say though that I have ridden with the Presta version of the gauge in place for over 100 miles at speeds up to 40 mph and it has continued to perform flawlessly. Seal is perfect even over many weeks. Changes in the wheel calibration factor (so called constant!) are detected down to 0.02 rev/km.

There are many ways in which the pressure- monitoring method can be applied, but I currently favor the use of the pressure coefficient. This is determined by simply riding a calibration course at two tire pressures. For my wheel the coefficient is negative 0.011 rev/km/kPa of pressure change. Note that this coefficient is independent of changes in bicycle weight and temperature, and seems to remain valid for many months. If weight and pressure are kept constant, the calibration factor itself is quite constant.

A typical application of the coefficient method is as follows. The night before a measurement I pump up the tire and fit the gauge to find a pressure of 590 kPa. I put the bicycle outside for a cold night and find in the early morning that pressure has dropped to 540 kPa. By the time I do the calibration though at around 10:15 am, temperature and pressure have risen to 3 deg C and 570 kPa, respectively, and the calibration is 480.00 rev/km. The 5-km course is a 90-min drive away, and I do not get started with the measurement until 1:30 pm, when temperature and pressure have risen again to 14 deg C and 580 kPa. I therefore use 479.89 rev/km (480 – 0.011 x 10) as the calibration factor to calculate the distance for the ride. It is unusual for pressure to change significantly over a 5-km course, but in this case I find that pressure has dropped to 570 kPa. I therefore determine that the average pressure was 575 kPa and extend the ride by 0.275 rev [(-0.011) x (-5) x 5].
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