The invention concerns a line for assembling tyres (P) and their wheels (R) to obtain mounted assemblies (E), comprising stations (2P and 2R) lubricating the seats and the rims of the tyres (P) and the wheels (R) respectively, a machine (3) mounting said tyres (P) on said wheels (R), a device (4) inflating the assemblies (E), the latter being transported from one station to the next by conveying means (1a, 1), characterised in that immediately after the inflating machine (4) conveying means (1) are provided wherein is arranged at least one compressed air curtain ramp (5) operating on the radially lower part of the assembly (E) horizontally placed on the conveying means (1).