Building the carcass structure of tyres for vehicle wheels includes associating, each end edge of a carcass ply, at least one respective annular reinforcement structure formed by depositing along a circumferential direction a plurality of reinforcement elements having a first length. Such elements are cut to size from a reinforced continuous band-like element fed to a cutting group arranged at a first operative position adapted to allow a barycentric grip of the reinforcement elements. The cutting group can translate along a feeding direction of the band-like element to a second operative position for cutting to size a plurality of second reinforcement elements having a second length different from the first length. The second operative position is defined on the basis of the second length, so as to have a barycentric grip of the second reinforcement elements too.