Derny

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Derny publicity material

A Derny is a motorized bicycle designed and built for motor-paced track cycling events (eg: motor-paced races in six-day and Keirin racing) or motor-paced road races.

It is driven by both a 90cc engine and by being pedalled through a fixed gear, typically of 70 teeth on the front chainring and 11 on the sprocket on the back wheel. The combination allows for smooth acceleration and slowing, important when the front wheel of the rider taking pace is only centimetres from the pacer's back wheel. A further feature is a coupling between the motor and the back wheel which ensures that the machine will not stop dead if the motor stops or seizes up.

The first Dernys were built by "Roger Derny et Fils" of Paris, France in 1938. That firm is no longer in business and the name "Derny" is now applied to all such vehicles, regardless of manufacturer. It is the word used by the Larousse dictionary as a generic term for a small pacing motorcycle used in cycle races. There have been several attempts to copy or improve on the original Derny. One, the Burdin, was briefly successful but proved not strong enough for repeated fast riding on the steep tracks used in six-day racing. Modern machines are now made by a small company in Neerpelt, Belgium, and the dernys used on the track now are either wholly new or have the original frames but new 90cc engines.

On a Derny, the driver sits close to the back of the bike in an upright position to provide an envelope of low wind resistance for the cyclist 'drafting' or slipstreaming behind. The machine has to be pushed and bump-started. It can then pace riders up to about 90kmh, although speeds in races rarely exceed 80kmh.

For most derny races, the cyclist sits in the slipstream of the derny for the duration of the event. In the keirin track race , common in Japan and now familiar elsewhere, the derny is used to bring a number of riders up to speed, at which point the derny pulls off and the race finishes without a pacer. Some riders also train behind a derny on the road.

A small group of semi-professional pacers travels around Europe for the winter six-day season. Most are in their 60s and 70s and some have been pacing for more than 40 years. The best known pacers are Bruno Walrave and Joop Zijlaard. Zijlaard, from Rotterdam, Holland, calls pacing his "paid hobby". His main income is from a fish restaurant in the city. He is father-in-law of the former world cycling champion Leontien van Moorsel, also Dutch.

In most of its later history, 560km Bordeaux-Paris Classic road race was motor-paced using dernys from half-distance. Other important races on the road behind dernys have included the Critérium des As in Paris.