What is a Derny?

You ever see that weird motorcycle / bicycle leading out racers on the track?  Well its called a Derny.

From Wikipedia ...

"A Derny is a motorized bicycle for motor-paced cycling events such as during six-day and Keirin racing, or motor-paced road races. It is driven by a 98cc Zurcher two-stroke 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 rider taking pace is centimetres from the pacer's shielded back wheel. A coupling between the motor and the back wheel ensures the machine will not stop dead if the motor seizes. Top speed, with rider pedalling, is up to 50kph, depending on gearing."

UCI Track World Cup 2011 - The Derny Explained from British Cycling on Vimeo.
Many casual observers of track cycling might have seen the Derny, and the Keirin race, but there's a good chance that they won't know how it works or what it's for.

Matt Rendell talks to the National Cycling Centre's derny driver, and asks him to give the low down.