A green tyre disposed on a toroidal support is introduced into a vulcanisation mould. The mould is closed through axial approaching of a pair of half shells acting against the sidewalls and the tread band of the tyre. Circumferential sectors set to operate against the tyre tread band are maintained spaced apart from the tread band itself during admission of a working fluid designed to press the tyre against the toroidal support. Subsequently the sectors are centripetally approached to cause penetration of forming ridges movable in through slits into the tread band, concurrently with a step of full moulding and vulcanisation of the tyre carried out through admission of steam under pressure into the tyre itself.