The Jones Counter is a device fitted to the front wheel of a bicycle that counts the revolutions of the wheel. It was invented in 1971 by Alan Jones in order to measure the length of road running race courses. The counter has gears that drive a mechanical digital counter. One count typically corresponds to about 1/20th of a wheel revolution (this varies if a different gear ratio is used); this provides a resolution of about 10 cm in course length, although overall accuracy, depending on calibration and other factors, is lower, but normally better than 1 part in 1,000.
Clain Jones Counter
On the right is the original production version, manufactured by Alan Jones's son Clain from 1973 to 1982. The gearing produces 20 counts per revolution of the bicycle wheel.
NYRRC Jones Counter
Production was taken over by New York Road Runners from 1983 to approximately 1990.
Paul Oerth took up production in approximately 1990 and continued to about 2006. These models have a different gear ratio (260/11 counts per wheel revolution). In 2006, production of the necessary gears ceased, and an alternative plastic-encapsulated set of gears was introduced. This was short-lived, and the Oerth model went out of production.
The Jones-Oerth-Lacroix Counter
The JOL counter is a variation of the Jones-Oerth model. Created by Laurent Lacroix in 2000, its distinguishing feature is a 27" rotary cable that allows the user to mount the Veeder-Root Counter on the handlebars.
Jones Counter model JR
The gearing (260/11 counts per wheel revolution) is identical to that of the Jones-Oerth model.
Use for measuring road-race courses
To measure road-race courses, the counter is fitted to a bicycle between the left fork leg and the front wheel. The tab or tabs on the large ring gear engage with the spokes, thus providing drive to a Veeder-Root counter.
Before the counter is used, the bicycle must first be calibrated by being ridden on a straight section of road between marks whose separation has been accurately measured by steel tape. A calibration can then be calculated in terms of counts per kilometer. Next, the bicycle is ridden over the race course to determine its length. Finally, the bicycle is recalibrated by riding again over the calibration distance. This is done to check for changes in bicycle-wheel diameter due to temperature changes, air leakage, and other causes.