The Jones Counter is a type of bicycle odometer which adds the function of a surveyor's wheel to a bicycle. It was developed in 1971 by Alan Jones to accurately measure the length of road running race courses.[1] The counter has gears that drive a mechanical digital counter. One count typically corresponds to about 1/20 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.
Almost all road running courses in the world are measured with this device. The Jones Counter has been used to measure all Olympic Marathon courses since the 1976 Montreal Olympics except for the 1980 Moscow Olympics. In addition, it has often been used to measure Olympic Road Race Walking Courses.
The original production version was manufactured by Alan Jones's son Clain from 1973 to 1982. The gearing produces 20 counts per revolution of the bicycle wheel.
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 JOL counter is a variation of the Jones-Oerth model. Created by Laurent Lacroix in 2000,[2][3] its distinguishing feature is a 27" rotary cable that allows the user to mount the Veeder-Root Counter on the handlebars.
Development of a new model started in 2007.[4] The first production units became available in April 2008 and were used for the measurement of the London Marathon, which took place on April 13, 2008.
The gearing (260/11 counts per wheel revolution) is identical to that of the Jones-Oerth model.
To measure road-race courses, the counter is fitted to a bicycle between the left fork leg and the front wheel.[5] The tab or tabs on the large ring gear engage with the spokes, thus providing drive to a Veeder-Root counter.
Antes de utilizar el contador, primero se debe calibrar la bicicleta conduciéndola por un tramo recto de la carretera entre marcas cuya separación haya sido medida con precisión con cinta de acero. Luego se puede calcular una calibración en términos de cuentas por kilómetro. A continuación, se recorre la bicicleta por la pista de carreras para determinar su longitud. Finalmente, la bicicleta se recalibra recorriendo de nuevo la distancia de calibración. Esto se hace para comprobar si hay cambios en el diámetro de las ruedas de la bicicleta debido a cambios de temperatura, fugas de aire y otras causas.