Mould for a tyre of the type comprising a tread and two side walls, the mould comprising: lower and upper portions which are intended for moulding at least the side walls of the tyre and movable at least axially relative to one another between a close-together position for moulding the tyre and a distanced position for extracting said tyre from the mould, and a plurality of central sectors which are in axial contact with the lower and upper portions in their close-together moulding position and are intended to ensure the moulding of at least a central portion of the tread of said tyre, said sectors being distributed in the circumferential direction and movable relative to the lower and upper portions, characterized in that for each sector, the mould furthermore comprises: a member for permanently coupling said sector to the upper portion and integral with said upper portion, and a member for temporarily coupling said sector to the lower portion and integral with said lower portion, said coupling members (20, 22) being configured so as to obtain: during an axial distancing movement of the lower and upper portions from their close-together moulding position, a radial displacement of said sector toward the outside followed by an angular pivoting of said sector towards the outside under the effect of its own weight, around an axis perpendicular to said directions of axial and radial displacement, and during an axial approaching movement of the lower and upper portions from their distanced position for extraction from the mould, reverse movements of said sector. lower and upper portions which are intended for moulding at least the side walls of the tyre and movable at least axially relative to one another between a close-together position for moulding the tyre and a distanced position for extracting said tyre from the mould, and a plurality of central sectors which are in axial contact with the lower and upper portions in their close-together moulding position and are intended to ensure the moulding of at least a central portion of the tread of said tyre, said sectors being distributed in the circumferential direction and movable relative to the lower and upper portions, characterized in that for each sector, the mould furthermore comprises: a member for permanently coupling said sector to the upper portion and integral with said upper portion, and a member for temporarily coupling said sector to the lower portion and integral with said lower portion, said coupling members (20, 22) being configured so as to obtain: during an axial distancing movement of the lower and upper portions from their close-together moulding position, a radial displacement of said sector toward the outside followed by an angular pivoting of said sector towards the outside under the effect of its own weight, around an axis perpendicular to said directions of axial and radial displacement, and during an axial approaching movement of the lower and upper portions from their distanced position for extraction from the mould, reverse movements of said sector. during an axial distancing movement of the lower and upper portions from their close-together moulding position, a radial displacement of said sector toward the outside followed by an angular pivoting of said sector towards the outside under the effect of its own weight, around an axis perpendicular to said directions of axial and radial displacement, and during an axial approaching movement of the lower and upper portions from their distanced position for extraction from the mould, reverse movements of said sector.