A pair of annular inserts of elastomeric material is circumferentially applied by spiraling around a laying surface of an auxiliary drum. Then a plurality of strip-like elements disposed in parallel side by side relationship with each other in the circumferential extension of the laying surface is applied onto the auxiliary drum, so as to form at least one first belt layer. Respectively opposite end portions of each strip-like element are radially superposed, each against one of the annular inserts, so that each of the annular inserts projects from a respective end edge of the strip-like element. The cap structure formed on the auxiliary drum is coupled to a carcass structure through toroidal conformation of the latter, in such a manner that the radially external ends of sidewall portions previously manufactured on the carcass plies are associated with the axially external ends of the annular inserts.

In a process for building tires, a carcass structure which includes at least one carcass ply and a belt structure, is formed. Manufacture of the belt structure includes: forming a first portion of at least one cushion insert through spiralling of a continuous elongated element; forming at least one first belt layer in a radially external position to the first portion in such a manner that the first portion axially projects from one of the axially opposite side edges of the first belt layer, forming a second portion of the cushion insert through spiralling of a continuous elongated element in a radially external position to the side edge of the first belt layer and to a stretch of the first portion projecting from the side edge itself, so as to enclose the side edge between the first and second portions of the cushion insert.

A pair of annular inserts of elastomeric material is circumferentially applied by spiraling around a laying surface of an auxiliary drum. Then a plurality of strip-like elements disposed in parallel side by side relationship with each other in the circumferential extension of the laying surface is applied onto the auxiliary drum, so as to form at least one first belt layer. Respectively opposite end portions of each strip-like element are radially superposed, each against one of the annular inserts, so that each of the annular inserts projects from a respective end edge of the strip-like element. The cap structure formed on the auxiliary drum is coupled to a carcass structure through toroidal conformation of the latter, in such a manner that the radially external ends of sidewall portions previously manufactured on the carcass plies are associated with the axially external ends of the annular inserts.