Clamping device, in particular for clamping a saddle for a bicycle, comprising: - a clamp which defines a central axis and is intended for substantially coaxially enclosing a part to be clamped, in particular a saddle post tube which is open in such a way that it has two ends (11, 12) which can be brought closer together to enclose the part to be clamped, and - a lever, which is mounted to pivot on the ends (11, 12) of the clamp about a pivoting axis extending substantially perpendicularly to the central axis, and which is connected to the clamp by a cam system operable by pivoting the lever about the pivoting axis between an open position, in which the clamp is released, and a closed position, in which the clamp is tightened; wherein the cam system includes at least one pair of cam parts associating a cam surface (33, 34) and a cam follower surface (25, 26), which are each generally helical by wrapping around the pivoting axis and which are respectively rotationally linked to each other about the pivoting axis of the clamp and the lever; wherein the cam surface (33, 34) of the or each pair of cam parts in the cam system comprises: - a first surface portion (33.1) against which the associated cam follower surface (25, 26) is pressed along the pivoting axis both when the lever is in the open position and when the lever is tilted from the open position to the closed position, and - a second surface portion (33.2), which is connected to the first surface portion (33.1) by a third surface portion (33.3) of the cam surface, and against which the associated cam follower surface is pressed along the pivoting axis both when the lever is in the closed position and when the lever is tilted from the closed position to the open position; wherein the cam follower surface (25, 26) of the or each pair of cam parts in the cam system comprises a main part (25.1, 26.1), which is helical, centred on the pivoting axis and having a constant pitch, and which is pressed along the pivoting axis against the second surface portion (33.2) of the associated cam surface (33, 34) when the lever is in the closed position; wherein the second portion of surface (33.2) of cam surface (33, 34) of the or each pair of cam parts in the cam system has a pitch which is substantially equal to the constant pitch of the main part (25.1, 26.1) of the associated cam follower surface (25, 26); and wherein the cam surface (33, 34) of the or each pair of cam parts in the cam system defines a bearing helix to which bearing stresses between the cam surface and the associated cam follower surface (25, 26) apply, which bearing helix winds around the pivoting axis extending at least partially over the first (33.1) and second (33.2) surface portions of the cam surface, characterized in that of the cam surface (33, 34) of the or each pair of the cam system has a helix angle (β 33A), measured with respect to a plane perpendicular to the pivoting axis, which is larger on the first surface portion (33.1) of the cam surface than on the second portion (33.2) of the cam surface. - a clamp which defines a central axis and is intended for substantially coaxially enclosing a part to be clamped, in particular a saddle post tube which is open in such a way that it has two ends (11, 12) which can be brought closer together to enclose the part to be clamped, and - a lever, which is mounted to pivot on the ends (11, 12) of the clamp about a pivoting axis extending substantially perpendicularly to the central axis, and which is connected to the clamp by a cam system operable by pivoting the lever about the pivoting axis between an open position, in which the clamp is released, and a closed position, in which the clamp is tightened; - a first surface portion (33.1) against which the associated cam follower surface (25, 26) is pressed along the pivoting axis both when the lever is in the open position and when the lever is tilted from the open position to the closed position, and - a second surface portion (33.2), which is connected to the first surface portion (33.1) by a third surface portion (33.3) of the cam surface, and against which the associated cam follower surface is pressed along the pivoting axis both when the lever is in the closed position and when the lever is tilted from the closed position to the open position;