Small two-stroke motorcycle used for motor-paced cycle racing on the track and, more rarely, on the road. Its main distinguishing features are that the speed is controlled by the rider pedalling a large ratio fixed gear rather than a hand throttle, so that speed changes are readily accommodated by the rider on the single-gear, brakeless track bike behind. They are usually also fitted with a roller behind the rear mudguard so that the paced rider can get as close as possible without worrying about the consequences of touching wheels. Since motor-paced racing is no longer a world championship discipline, these machines are mainly seen at six-day races and for the keirin, although they are being supplanted by quieter, less smelly electrically assisted bikes for the latter.