What is "keirin"

n. (context cycling English) A form of track cycling originating in Japan, where riders must initially race behind a motorised pace-setter.

is a form of motor-paced cycle racing in which track cyclists sprint for victory following a speed-controlled start behind a motorized or non-motorized pacer. It was developed in Japan around 1948 for gambling purposes and became an official event at the 2000 Olympics in Sydney, Australia.

Races are about long: 8 laps on a track, 6 laps on a track, 5 laps on a track. Lots are drawn to determine starting positions for the sprint riders behind the pacer, which is usually a motorcycle, but can be a derny, electric bicycle or tandem bicycle. Riders must remain behind the pacer for a predetermined number of laps. Initially it makes circuits at about , gradually increasing to about . The pacer usually leaves the track approximately before the end. The winner's finishing speed is around .

Competition keirin races are often conducted over several rounds with one final. Sometimes eliminated cyclists get the opportunity to try again in the repechages.