A bicycle includes a lower frame member and an upper frame member connected to a head tube. The lower frame member includes a down tube, a bottom bracket, and chain stays. The upper frame member includes a top tube, seat stays, and a passage formed in part by a first side wall and a second side wall. The first and second side walls include a first and second openings, respectively. A seat tube extends in an upward direction from the bottom bracket and through the passage. The seat tube includes an opening that extends laterally therethrough. A passive pivot assembly secures the seat tube within the passage, and includes a guide sleeve that extends through the first opening, through the opening in the seat tube, and through the second opening. One or more fasteners secure the guide sleeve to the upper frame member.