Tractor/trailer combinations

In combination, a tractor unit and a trailer unit, the tractor unit and the trailer unit being coupled by a connection device which permits of relative angular movement between the tractor unit and the trailer unit about a generally upright axis, the connection device including a connecting pin which extends from a connecting surface of one of the trailer unit and the tractor unit, and is in use received in an opening in a connecting surface of the other of the tractor unit and the trailer unit, the connecting pin including a sensor device to sense loads imposed on the connecting pin as the trailer unit tends to decelerate or accelerate relative to the tractor unit, there being a control system, including a controller, the controller receiving signals from the sensor device of the connecting pin representative of the loads imposed on the connecting pin, the trailer unit including a pair of ground engaging wheels, one at each side of the trailer unit, at least one electrical motive machine which is capable of being electrically driven by power from an electrical storage device to provide drive to drive at least one of the ground engaging wheels to tend to accelerate the trailer relative to the tractor unit, and of generating electrical power for storage by the electrical storage device, in response to the trailer unit tending to accelerate relative to the tractor unit, and wherein the controller in use, controls the electrical motive machine in response to the signals from the sensor device to reduce the loads imposed on the connecting pin, wherein the connecting pin has a generally circular cross-section and wherein the sensor device includes spaced apart first and second sensor parts, wherein the first and second sensor parts are at spaced apart diametrically opposed locations relative to the circular cross section of the connecting pin and are configured to sense loads at diametrically opposite positions of the connecting pin during relative angular movement between the tractor unit and the trailer unit.