The bead breaking unit (1) for tyre changing machines includes an arm (2) associated revolving with a supporting structure (3), a bead breaking tool (4) associated with the arm (2), at least a movement device (6) operatively associated with the arm (2) and suitable for moving the arm (2) from a disengaging position, wherein the bead breaking tool (4) is substantially moved away from a tyre of a wheel to undergo bead breaking, to an operating position, wherein the bead breaking tool (4) is suitable for engaging on the tyre, the arm (2) having at least a tilting device (7) of the bead breaking tool (4) suitable for allowing the partial rotation of the bead breaking tool (4) when it is engaged on the tyre, an adjustment arrangement (11) for adjusting the angular position of the bead breaking tool (4) and at least an activation/deactivation device (12) of the tilting device (7).