A vehicle having a load frame with wheels, a drive frame, a drive wheel, a non-driven rigid castor wheel, and a pivot link assembly. The drive wheel and non-driven rigid castor wheel are each fixed to move with the drive frame. The pivot link assembly couples the drive frame to the load frame to permit the drive frame to move vertically relative to the load frame. The pivot link assembly also has a first pivot axis about which the drive frame is rotatable relative to the load frame.