Method for assembling a suspension system of a motorcycle provided with a frame, two front steering wheels, a steering pipe rotatably connected to the frame and rigidly connected to two supporting assemblies, one for each front steering wheel, on each of the supporting assembly being constrained fixed portions or rods of two telescopic elements (22, 24), comprising the successive steps of: - obtaining, on the sliding portion of a first of said telescopic elements of each pair of telescopic elements (22, 24), a plurality of holes (26A, 26B, 26C), - coupling said holes (26A, 26B, 26C) of the first telescopic element with corresponding holes (26A, 26B, 26C) obtained on the sliding portion of the second telescopic element of each pair of telescopic elements (22, 24), so as to obtain a mutual connection, through fixing means (42A, 42B, 42C; 52; 54A, 54B, 54C; 56A), of said first and second telescopic elements, wherein said fixing means comprise a plurality of screws (42A, 42B, 42C) with relative nuts (54A, 54B, 54C), wherein said mutual connection is obtained by the steps of: - inserting a peg, at least in the pair of lower connection holes arranged farthest down on the two telescopic elements (22,24), wherein the internal diameter of each of such lower connection holes is substantially the same size as the external diameter of each peg, whereas the peg itself is axially provided with a through hole for the introduction of a screw, - bring together the pair of lower connection holes of the telescopic elements (22,24), without forcing, through the screw and a relative nut, - inserting the fixed portions or rods of the telescopic elements (22,24) inside clamps (18,20) obtained on the respective support assembly, - clamping the clamps (18,20), - applying a blocking torque to the screws (42B,42C) and the relative nuts (54B,54C) of the remaining pairs of connection holes (26B,26C) of the telescopic elements (22, 24). - obtaining, on the sliding portion of a first of said telescopic elements of each pair of telescopic elements (22, 24), a plurality of holes (26A, 26B, 26C), - coupling said holes (26A, 26B, 26C) of the first telescopic element with corresponding holes (26A, 26B, 26C) obtained on the sliding portion of the second telescopic element of each pair of telescopic elements (22, 24), so as to obtain a mutual connection, through fixing means (42A, 42B, 42C; 52; 54A, 54B, 54C; 56A), of said first and second telescopic elements, wherein said fixing means comprise a plurality of screws (42A, 42B, 42C) with relative nuts (54A, 54B, 54C), - inserting a peg, at least in the pair of lower connection holes arranged farthest down on the two telescopic elements (22,24), wherein the internal diameter of each of such lower connection holes is substantially the same size as the external diameter of each peg, whereas the peg itself is axially provided with a through hole for the introduction of a screw, - bring together the pair of lower connection holes of the telescopic elements (22,24), without forcing, through the screw and a relative nut, - inserting the fixed portions or rods of the telescopic elements (22,24) inside clamps (18,20) obtained on the respective support assembly, - clamping the clamps (18,20), - applying a blocking torque to the screws (42B,42C) and the relative nuts (54B,54C) of the remaining pairs of connection holes (26B,26C) of the telescopic elements (22, 24).