A seatpost assembly, including a first seatpost portion, a second seatpost portion axially displaceable relative to the first seatpost portion along an axial axis, and an engagement element with a circumferential coil portion having a first termination and a second termination. The engagement element may be elastically deflected in a relaxing direction toward an engaged orientation to provide restraint of the axial displacement at a restraining interface with one of the first and second seatpost portions; and in a deflecting direction toward a released orientation for reduced restraint. The engagement element has an axially maintained engagement with the other one of the first seatpost portion. Where one of: (i) the released orientation corresponds to a radially outwardly expanded orientation of the engagement element relative to the deflected position; and (ii) the released orientation corresponds to a radially inwardly contracted orientation of the engagement element relative to the deflected position.