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why do they call it a 5th wheel

The term fifth wheel comes from a similar coupling used on four-wheel and. The device allowed the
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. Fifth wheels were originally not a complete circle and were hand forged. When mass production of buggy parts began in the early 19th century, fifth wheels were among the first products to be made. There were a number of patents awarded for fifth-wheel design. Edward and Charles Everett, Quincy, Illinois patented a type of fifth wheel in 1850, followed by Gutches' metallic head block and fifth wheel in 1870 and Wilcox fifth wheel in 1905. [ 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. It was submitted for patent in 1915, and finalized in 1916. Herman Farr invented it, and Martin hooked up with him and became the assignee. When they formed the Martin Fifth Wheel company Martin was president and Farr was named secretary. The 5th wheel was Farr's invention. Martin capitalized on it. "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 trailerunlike todays 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. " The helped to make the Martin Rocking 5th Wheel a success by installing them on their popular new semi-trailer design. August Fruehauf invented the semi-trailer in 1914 with their own 5th wheel hitch. They adopted the Martin Rocking 5th wheel in 1916. By 1916 Fruehauf was producing semi-trailers in tandem with Federal Truck. These two Detroit companies also contracted with the military in WWI sending a convoy of supplies, men and equipment from Detroit to Norfolk, Virginia shipyards for travel to the front in Europe. Fruehauf's success with semi-trailer sales surpassed the million dollar sales mark by 1920. Opening a branch in Chicago and later in Des Moines their trailers and hence, the Martin Rocking 5th Wheel became the top selling commercial vehicle of this era.

Fruehauf's slogan, "A Horse can pull more than it can carry, so can a truck" became their advertising motto. Merchants, manufacturers and businesses in every industry clamored for a semi-trailer and the shuttle concept introduced by Fruehauf using one tractor truck and 2 or more semi-trailers. Fruehauf used the Martin Rocking 5th Wheel up until at least 1919. Early that year, the manual coupler was introduced to the industry by Fruehauf and the jacks acting as front supports for the semi-trailer were supplanted by wheels, raised and lowered manually. In 1926, Fruehauf introduced the automatic semi-trailer in which the coupling and the uncoupling of the tractor were accomplished mechanically by the motion of the tractor. Fruehauf's introduction of the automatic semi-trailer was instantly recognized by transportation experts as a major contribution to the industry. The automatic semi-trailer coupling patented by Fruehauf dominated the semi-trailer market until the 's assets were sold in bankruptcy to Wabash National in 1997. Later documentation for a patent of a fifth wheel is in patent number 2,053,812 issued to Charles E. Bradshaw of, Virginia, filed March 18, 1936 and granted September 8, 1936. One third of the patent was assigned to Charles Martin, also of Wellville. Today's fifth wheels allow the trailers to slide into the fifth wheel and lock into it, and are a very reliable unit when maintained and serviced properly.

The engagement of the king pin into the fifth-wheel locking mechanism is the only means of connection between tractor and trailer; no other device or safety mechanism is used. Couplers and use safety chains in the event of a trailer separation while going down the road. Trailer-to-trailer connection can also be made by using fifth wheels. First I have never seen a fifth wheel trailer that had half of its weight being supported by the tow vehicle, more like 18-25%MAX. I am talking R. V's now, not semi trailers, but I don't even think that they have 50% of their weight on the pin fully loaded. I was refering to all 5th wheel setups, that's why I said "up to 50%". Most travel trailers are as you said in the under 25% range, with some down to 15% or so. As for as semi trucks, take a good look at how tractor trailers are set up. Yes, they cary about 50% of the trailer weight on the truck's rear axles (you have to subtract the weight of the tractor's rear end from the trailer weight to get the exact amount of trailer weight it can cary) and the other half (about) of the trailer is on it's rear wheels. These dual wheel axles cary about 15,000 pounds each, with about 7,500 pounds on the single wheel front axle, depending on state highway weight limits per axle. Some trucks can cary twice that weight per axle, and you can add extra axles for super heavy weight.

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