A high performance synchronous transmission to be used aboard a motorcycle for transmitting the motion generated by an engine to a driving wheel, between a crankshaft and a hub shaft parallel therebetween and perpendicular to the median plane of the motorcycle, comprising on the crankshaft a centrifugal clutch, for the automatic engagement of the first speed above a predetermined rotation regime, and a driving pulley apt to transmit the motion through a subsequent kinematic chain, is provided with a coupling between crankshaft and driving pulley which connects them directly, by determining with its own engagement the exclusion of said centrifugal clutch, said coupling being controlled in disengagement when a control lever is in active position.