Device for centring the rim of a wheel on the wheel-holder unit of a tyre changer machine

A device for centring the rim of a wheel on the wheel-holder unit (101) of a tyre changer machine (100) comprises a first plate (4) which can be positioned above the wheel-holder unit (101) and coupled there for rotating integrally with it and equipped with a through opening (4a) which can be aligned with a central hole (101a) of the wheel-holder unit (101) for allowing the insertion of a clamping rod (107) in the hole through the opening (4a), for locking the rim on the wheel-holder unit (101). The device also comprises a second plate (5) forming a supporting surface (E) for the rim (2) and equipped with its own through opening (5a), the second plate (5) being slidably positioned above the first plate (4) and the device also comprises friction reduction means (17) operatively interposed between the first plate (4) and the second plate (5) for facilitating their sliding relative to each other.