Abstract: An add-on wheel/axle assembly for truck-type vehicles for reducing the effective axle load of the vehicle allowing the carrying of greater payloads without violating governmentally imposed road restrictions. The assembly includes a hydraulically actuatable articulated arm assembly where one end of a first arm link is pivotally joined to opposed sides of the truck frame proximate its rear end and with wheels mounted on stub axles affixed to the other ends of said arm assemblies. A cross-member offset by a predetermined distance from the stub axles joins the arm assemblies together and a hydraulic cylinder is operatively coupled between the truck frame and the articulated arms for extending and retracting the wheels between a ground-engaging disposition and an elevated disposition. Tie bars and associated bell cranks also cooperate with the articulated arms to draw the wheels in a straddling disposition relative to the truck frame when the wheels are in their elevated disposition.