why is a fifth wheel called a fifth wheel
Fifth-wheel coupling The term fifth wheel comes from a similar coupling used on four-wheel horse-drawn carriages and wagons. The device allowed the front axle assembly to pivot in the horizontal plane, to facilitate turning. Basically a wheel was placed on the rear frame section of the truck, which back then only had four wheels; this wheel that was placed on the frame was the "fifth wheel", hence the name. The trailer needed to be raised so that the trailer's pin would be able to drop into the central hole of the fifth wheel.
Tire rotation Tire rotation is the practice of moving the wheels and tires of an automobile from one position to another, to ensure even tire wear.[citation needed] Even tire wear is desirable to extend the useful life of a set of tires.