A synchronous transmission to be used aboard a motorcycle for transmitting the motion generated by an engine to a driving wheel, between a crankshaft and hub shaft, comprising: • a clutch set assembled on said crankshaft; • a transmission wheel revolvingly coupled to said crankshaft connected to the hub shaft by means of a kinematic chain, • wherein said clutch set comprises: • a clutch element for the automatic engagement of the first speed, revolvingly coupled to said crankshaft; o a first centrifugal clutch (10,7,8) associated to said clutch element; o a second centrifugal clutch (25,15,16) associated to said clutch element; said first centrifugal clutch (10,7,8) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a first rotation regime (N 1) of the crankshaft, and said second centrifugal clutch (25,15,16) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a second rotation regime (N 2) of the crankshaft; said second rotation regime (N 2) being lower than said first rotation regime (N 1); • a selection set (11,22,77) of said second centrifugal clutch (25,15,16) which comprises at least a locking element and which results to be configured to pass selectively from: o a first configuration wherein said locking element is engaged with said second centrifugal clutch so as to lock radially said second centrifugal clutch, by preventing the same to engage said clutch element, to o a second configuration wherein said locking element is disengaged from said second centrifugal clutch so as to allow the operation of the same. • a clutch set assembled on said crankshaft; • a transmission wheel revolvingly coupled to said crankshaft connected to the hub shaft by means of a kinematic chain, • wherein said clutch set comprises: • a clutch element for the automatic engagement of the first speed, revolvingly coupled to said crankshaft; o a first centrifugal clutch (10,7,8) associated to said clutch element; o a second centrifugal clutch (25,15,16) associated to said clutch element; said first centrifugal clutch (10,7,8) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a first rotation regime (N 1) of the crankshaft, and said second centrifugal clutch (25,15,16) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a second rotation regime (N 2) of the crankshaft; said second rotation regime (N 2) being lower than said first rotation regime (N 1); o a first centrifugal clutch (10,7,8) associated to said clutch element; o a second centrifugal clutch (25,15,16) associated to said clutch element; said first centrifugal clutch (10,7,8) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a first rotation regime (N 1) of the crankshaft, and said second centrifugal clutch (25,15,16) being arranged on the crankshaft so as to engage said clutch element upon reaching or exceeding a second rotation regime (N 2) of the crankshaft; said second rotation regime (N 2) being lower than said first rotation regime (N 1); • a selection set (11,22,77) of said second centrifugal clutch (25,15,16) which comprises at least a locking element and which results to be configured to pass selectively from: o a first configuration wherein said locking element is engaged with said second centrifugal clutch so as to lock radially said second centrifugal clutch, by preventing the same to engage said clutch element, to o a second configuration wherein said locking element is disengaged from said second centrifugal clutch so as to allow the operation of the same. o a first configuration wherein said locking element is engaged with said second centrifugal clutch so as to lock radially said second centrifugal clutch, by preventing the same to engage said clutch element, to o a second configuration wherein said locking element is disengaged from said second centrifugal clutch so as to allow the operation of the same.