A Derny is a type of motorcycle designed and built specifically for motor-paced track cycling events (motor-paced road, 6-Day and Keirin racing). On a Derny, the driver sits close to the back of the bike in an upright (almost standing) position to provide an envelope of low wind resistance for the cyclist drafting behind. There is sometimes a horizontal roller mounted to the rear of the bike to prevent crashes should the bicycle come in contact with the derny.
The first Dernys were built by Roger Derny and Sons 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 manufactuerer.
For most derny races, the cyclist drafts off the derny for the duration of the event. In some events, the derny is used to bring the bicycle up to speed, at which point the derny pulls off and the cyclist continues the race without a motorized pacer. For speed records, the bicycle used generally has a fixed gear and the gear ratio is too high to allow the cyclist to start from a stop, so dernys are used to provide starting assistance (though the current absolute world bicycle-speed records were set behind fairing-equipped automobiles).
A rider drafting behind a derny is known as a stayer , as is a bicyle designed or used for this kind of racing; and in a stayer race each rider trails a derny from beginning to end.
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