Servo hub unit with slipper function for a clutch of a handlebar vehicle comprising: - A hub adapted to be connected to an output shaft of a vehicle engine and having an axis of rotation; - A plurality of guides configured to provide translation of and to lock to rotation a plurality of friction discs, the guides being rigidly connected to the hub; - An axial stop flange for the plurality of friction discs rigidly connected to the hub; - A disc pressure flange movable in a direction parallel to the guides to press the plurality of discs against the axial stop flange or release the plurality of discs from the axial stop flange - At least one spring to press the disc pressure flamge towards the axial stop flange and arranged against a stop rigidly connected to the hub; Wherein: the hub defines at least a first and a second track (12,13) facing in an axial direction and arranged in a direction not parallel to the axis of rotation and the disc pressure flange comprises at least one pin projecting in a substantially radial direction and arranged in contact with: the first track having a first inclination such as to convert a first torque applied to the disc pressure flange by the discs into a first axial load applied by the disc pressure flange to press the discs against the axial stop flange and have a servo assisting effect when closing the clutch; the second track having a second inclination such as to convert a second torque applied by the hub into a second axial load applied to distance the disc pressure flange from the axial stop flange to disengage the discs and allow a slipper function; and characterised in that, the disc pressure flange comprises a plurality of teeth facing the axial stop flange and engaging on at least one disc so that the latter applies said first torque. - A hub adapted to be connected to an output shaft of a vehicle engine and having an axis of rotation; - A plurality of guides configured to provide translation of and to lock to rotation a plurality of friction discs, the guides being rigidly connected to the hub; - An axial stop flange for the plurality of friction discs rigidly connected to the hub; - A disc pressure flange movable in a direction parallel to the guides to press the plurality of discs against the axial stop flange or release the plurality of discs from the axial stop flange - At least one spring to press the disc pressure flamge towards the axial stop flange and arranged against a stop rigidly connected to the hub; Wherein: the hub defines at least a first and a second track (12,13) facing in an axial direction and arranged in a direction not parallel to the axis of rotation and the disc pressure flange comprises at least one pin projecting in a substantially radial direction and arranged in contact with: the first track having a first inclination such as to convert a first torque applied to the disc pressure flange by the discs into a first axial load applied by the disc pressure flange to press the discs against the axial stop flange and have a servo assisting effect when closing the clutch; the second track having a second inclination such as to convert a second torque applied by the hub into a second axial load applied to distance the disc pressure flange from the axial stop flange to disengage the discs and allow a slipper function; and characterised in that, the disc pressure flange comprises a plurality of teeth facing the axial stop flange and engaging on at least one disc so that the latter applies said first torque. the hub defines at least a first and a second track (12,13) facing in an axial direction and arranged in a direction not parallel to the axis of rotation and the disc pressure flange comprises at least one pin projecting in a substantially radial direction and arranged in contact with: the first track having a first inclination such as to convert a first torque applied to the disc pressure flange by the discs into a first axial load applied by the disc pressure flange to press the discs against the axial stop flange and have a servo assisting effect when closing the clutch; the second track having a second inclination such as to convert a second torque applied by the hub into a second axial load applied to distance the disc pressure flange from the axial stop flange to disengage the discs and allow a slipper function; and characterised in that, the disc pressure flange comprises a plurality of teeth facing the axial stop flange and engaging on at least one disc so that the latter applies said first torque. the first track having a first inclination such as to convert a first torque applied to the disc pressure flange by the discs into a first axial load applied by the disc pressure flange to press the discs against the axial stop flange and have a servo assisting effect when closing the clutch; the second track having a second inclination such as to convert a second torque applied by the hub into a second axial load applied to distance the disc pressure flange from the axial stop flange to disengage the discs and allow a slipper function; and characterised in that, the disc pressure flange comprises a plurality of teeth facing the axial stop flange and engaging on at least one disc so that the latter applies said first torque.