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The fifth wheel on a tractor unit, rear view Fifth wheel on the bottom of the trailer A fifth wheel, already coupled, side view. The fifth-wheel coupling provides the link between a semi-trailer and the towing truck, tractor unit, leading trailer or dolly.
The fifth wheel coupling or hitch provides the link between a fifth-wheel trailer and the towing truck. Newer fifth-wheel hitches are pivoted in two dimensions to ease hitching up and to give the truck and trailer more freedom of movement together.
The fifth-wheel trailer coupling on most tractor trucks is movable fore and aft, to allow adjustment in the weight distribution over its rear axle(s). [citation needed] Ubiquitous in Europe but less common in North America since the 1990s, is the cabover engine configuration, where the driver sits next to or over the engine. With changes in the ...
The towing vehicle has a wide coupling plate known as a fifth-wheel coupling bolted onto its chassis, on which the semi-trailer rests and pivots. As the tractor reverses under the trailer, a kingpin under the front of the trailer slides into a slot in the skid plate, and the jaws of the fifth wheel close onto it.
Thus, the weight of the vehicle tends to rotate the wheel about the kingpin back to this position. The kingpin inclination also contributes to the scrub radius of the steered wheel, the distance between the centre of the tyre contact patch and where the kingpin axis intersects the ground. If these points coincide, the scrub radius is zero.
An A-dolly has a single drawbar with a centred coupling. A C-dolly has two separate couplings side-by-side. Low loader dolly, equipped with a gooseneck type drawbar that attaches to the fifth wheel coupling on the rear of a prime mover to distribute the mass on the fifth wheel on the dolly between the prime mover and the wheels of the dolly ...
A fifth-wheel coupling is also referred to as a kingpin hitch and is a smaller version of the semi-trailer "fifth wheel". Though a fifth wheel and a gooseneck trailer look much the same, their method for coupling is different. A fifth wheel uses a large horseshoe-shaped coupling device mounted 1 foot (0.30 m) or more above the bed of the tow ...
The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is: T = Weight of towing vehicle including the vertical load on the fifth wheel R = Total weight of the loaded semi-trailer U = Vertical load on the fifth wheel g = Acceleration due to gravity (assumed to be 9.81 m/s 2 )