The invention relates to a motion transmission system of a bicycle, comprising a sprocket assembly (16) adapted to be mounted on a freewheel body (22) of a hub of a bicycle rear wheel and a bicycle chain (15) adapted to engage the sprockets (1-11) of the sprocket assembly (16). The sprocket assembly comprises at least eleven sprockets. The hub is able to rotate about a rotation axis (X) and comprises a plurality of spoke attachment seats and a fastening portion to a frame (53) of the bicycle. On the hub a predetermined axial distance is defined between a plane (Z), substantially perpendicular to said rotation axis (X), comprising the points of the spoke attachment seats closest to the freewheel body (22) and a plane (Y), substantially perpendicular to said rotation axis (X) and defined in the fastening portion to the frame (53), comprising the attachment points to the frame closest to the freewheel body (22). All of the sprockets of said sprocket assembly, when associated with the freewheel body, have an overall axial bulk that is lower than or equal to said predetermined axial distance. The chain (15) has a maximum thickness comprised between 4.6 mm and 5.8 mm.