Mould for vulcanising tyres for vehicles, comprising a first half-part and a second half-part that are axially opposite and mutually side-by-side along a geometric centring axis (X) in order to define a moulding cavity arranged to house a tyre being processed; wherein the first half-part and the second half-part are mutually couplable along a junction line ; wherein the moulding cavity has an internal wall extended concentrically around the geometric centring axis (X), characterized in that the moulding cavity carries a plurality of circumferentially-distributed slots , configured for defining corresponding ribs on a radially outer portion of the moulded tyre ; wherein each slot has an axially inner terminal portion arranged in proximity to an intermediate reference plane (P) orthogonal to the geometric centring axis (X), and an axially outer terminal portion spaced from the intermediate reference plane (P); wherein said plurality of slots comprises a first series of slots having the respective axially outer terminal portions in the first half-part and a second series of slots having the respective axially outer terminal portions in the second half-part , wherein the slots respectively belonging to the first and second series are circumferentially offset from each other and have the respective axially inner terminal portions equidistant from the intermediate reference plane (P); wherein the junction line is extended according to an undulating progression astride the intermediate reference plane (P), to form crests alternatively arranged on respectively opposite sides with respect to the intermediate reference plane (P); wherein each of the slots belonging to the first and to the second series is intersected in proximity to its axially inner terminal portion by one of the crests formed by the junction line . wherein the first half-part and the second half-part are mutually couplable along a junction line ; wherein the moulding cavity has an internal wall extended concentrically around the geometric centring axis (X), characterized in that the moulding cavity carries a plurality of circumferentially-distributed slots , configured for defining corresponding ribs on a radially outer portion of the moulded tyre ; wherein each slot has an axially inner terminal portion arranged in proximity to an intermediate reference plane (P) orthogonal to the geometric centring axis (X), and an axially outer terminal portion spaced from the intermediate reference plane (P); wherein said plurality of slots comprises a first series of slots having the respective axially outer terminal portions in the first half-part and a second series of slots having the respective axially outer terminal portions in the second half-part , wherein the slots respectively belonging to the first and second series are circumferentially offset from each other and have the respective axially inner terminal portions equidistant from the intermediate reference plane (P); wherein the junction line is extended according to an undulating progression astride the intermediate reference plane (P), to form crests alternatively arranged on respectively opposite sides with respect to the intermediate reference plane (P); wherein each of the slots belonging to the first and to the second series is intersected in proximity to its axially inner terminal portion by one of the crests formed by the junction line . <EOS>