Abstract: Selectively operable spiral cam wheels are positioned adjacent and rotate on a common axis with the drive wheels and are attachable to the drive wheels for progressively raising the wheelchair in response to rotation of the drive wheels in one direction and for progressively lowering the wheelchair in response to rotation of the drive wheels in the opposite direction. The spiral cam wheels are also attachable to the wheelchair frame so that the drive wheels are free to be rotated in the normal manner. A lifting arm is pivotally supported at one end on each side of the frame of the wheelchair and the other end is moved by the spiral cam wheels to progressively lift the casters of the wheelchair as the wheelchair is moved toward a curb to be traversed. Embodiments of the wheelchair are disclosed in which the wheelchair is raised as it is moved in a forward direction toward the curb, and in which the wheelchair is raised as it is moved in a rearward direction toward the curb.