Abstract: A wheelchair including: a frame including a backrest portion; and a drive wheel attached to the frame using an axle, wherein the axle is attached below the backrest portion and is configured to have the drive wheel rotate about the axle; a front caster connected to the frame and horizontally offset from the drive wheel; and a relative positioning mechanism connected to the frame and the front caster assembly, wherein the relative positioning mechanism is configured to locate the front caster assembly at two or more positions relative to the frame along a vertical direction.