About Keirin from Wikipedia;
- Races are about 2 kilometers long: 8 laps on a 250 m track, 6 laps on a 333 m track, 5 laps on a 400 m 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. Riders must remain behind the pacer for a predetermined number of laps. Initially it makes circuits at about 25 kilometres per hour (16 mph), gradually increasing to about 50 kilometres per hour (31 mph). The pacer usually leaves the track approximately 600–700 meters before the end. The winner's finishing speed is around 70 kilometres per hour (43 mph).