Keirin races involve up to 7 cyclists each (though the 2020 format has no races with more than 6). The cyclists follow a pace motorcycle for 3 laps (750 m); the motorcycle then pulls away and the cyclists race for another 3 laps. These distances are changed from the 2016 Games, shortening the paced section from 5.5 laps and lengthening the unpaced sprint from 2.5 laps. The motorcycle starts at 30 km/h and increases speed to 50 km/h before it pulls off.
The tournament consists of four main rounds (up from three in 2016) and a repechage:[1][2]
First round: Five heats of 6 cyclists each. The top 2 cyclists in each heat (10 total) advance to the second round; all others (20 cyclists) go to the repechage.
Repechage: Four heats of 5 cyclists each. The top 2 cyclists in each heat (8 total) rejoin the first-round winners in the second round. The other 12 cyclists are eliminated.
Second round: Three heats of 6 cyclists each. The top 4 cyclists in each heat (12 total) advance to the semifinals. The remaining 6 cyclists are eliminated.
Semifinals: Two heats of 6 cyclists each. The top 3 cyclists in each semifinal (6 total) advance to Final A; the bottom 3 cyclists from each semifinal go to Final B, out of medal contention.
Finals: Two finals. Final A consists of the top 6 cyclists, awarding medals and 4th through 6th place. Final B ranks the next 6 cyclists from 7th to 12th.
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