Back on the Big Road with JB Hunt...or UturnGirl Bolts

Origin
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. A wheel would be placed on the rear frame section of the truck, which at the time had only four wheels, making the additional wheel the "fifth wheel". 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.

The invention of the fifth wheel for motorized trucks is often credited to US inventor Charles H. Martin of the Martin Rocking Fifth Wheel Co. who invented the device in 1915. [1] It was submitted for patent in 1915 and finalized in 1916, with Herman Farr as inventor and Martin as assignee. When they formed the Martin Fifth Wheel company Martin was president and Farr was named secretary. "It's a fair question whether you really can consider the fifth wheel as a milestone separate from the semi-trailer. After all, the purpose of the fifth wheel is to link the tractor and the trailer; indeed, trailers existed before Charles H. Martin introduced the Martin Rocking Fifth Wheel in 1915. At the time, the fifth wheel literally was a wheel that moved with the trailer—unlike today’s technology that secures a kingpin. What makes the fifth wheel so important is the ability it gave fleet owners to attach large trailers to tractors easily and safely and the freedom it gave them to switch out trailers. Without a fifth wheel, the modern distribution system would look quite different as drop-and-hook would not be easy. The semi-trailer increased the capacity of trucks, but it was the fifth wheel that brought the flexibility for drivers to keep moving while receivers unloaded the loads they just delivered.

 

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