A moveable load-carrying assembly including a chassis (1) having a plurality of wheels (6) arranged as a first wheel set and a second wheel set, each wheel (6) being rotatable and swivellable relative to the chassis (1); the wheels (6) of the first wheel set being connected by a first linkage (21), and the wheels (6) of the second wheel set being connected by a second linkage (22); and wherein one of the wheels (6) of the second wheel set is linked to the opposite one of the wheels (6) of the first wheel set by a link (11) such that when one of the wheels (6) of the first wheel set is swivelled in one direction relative to the chassis (1), all the wheels (6) of the first wheel set swivel in that direction in unison, and all the wheels (6) of the second wheel set swivel in the opposite direction in unison. Means are included to provide three distinct modes of operation for a wheel set, the modes corresponding to straight-line travel, fully-steerable travel and a braking mode. The assembly also includes an apparatus for returning the steerable wheels to a straight-line position, comprising a first member (203) associated with a tie rod (202) operably connected to one or more steerable wheels, at least one further member (205, 206) pivotably associated with a fixed chassis member (201) and a resilient means (209) associated with the further member.