@ the 20% weight comments in this thread. 
Some people will believe anything.
Harry Monk:
IIRC, a typical fully-freighted artic with tri-axle trailer will show an axle weight of around 8 tonnes per trailer axle. A loaded trailer weighs around 36 tonnes, (44 tonnes minus the weight of the tractor) 24 tonnes of this is borne by the trailer axles and so around a third of the weight is borne by the fifth wheel.
They also used the term in the states when we were still using mainly rigids and their typical configuration has always been 5 axles 3+2.But having said that the 20% figure seems to be a breakpoint minimum to seperate an artic and itâs coupling from ballast tractor trailer or drawbar outfits 
in which case the term seems to make some sense although common sense would prevent anyone confusing the different types anyway and the terms tractor unit and semi trailer outfit versus the different types of truck and trailer outfit have been in common use just as much as the term fifth wheel and thereâs no way that anyone could confuse the different types or their coupling designs.
FWIW it says this on WikiâŚ
The term âfifth wheelâ 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 horizontal wheel or segment of a wheel called a fifth wheel sometimes forms an extended support to prevent the carriage from tipping; it consists of two parts rotating on each other about the kingbolt above the fore axle and beneath the body
Harry Monk:
FWIW it says this on WikiâŚThe term âfifth wheelâ 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.
Wiki is written by users, so info on it should be taken with a pinch of salt, but sounds about right to me?
What I donât get, why would a driver be asked this question to get a job driving a truck?
Can you drive this vehicle? YES. Do you know rules n regs? YES. Do you know why itâs called a 5th wheel? NO. Sorry then, we canât get you any work??
waynedl:
Harry Monk:
FWIW it says this on WikiâŚThe term âfifth wheelâ 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.
Wiki is written by users, so info on it should be taken with a pinch of salt, but sounds about right to me?
What I donât get, why would a driver be asked this question to get a job driving a truck?
Can you drive this vehicle? YES. Do you know rules n regs? YES. Do you know why itâs called a 5th wheel? NO. Sorry then, we canât get you any work??
That just about sums it up for me as well Wyane. All these assessments and BS questions serve no useful purpose at all.
I always thought that it was called a âfifthâ wheel because it was invented by Horatio charles edward Fifth, Inventor, (1893 - 1977). he is also credited with the dog clip, invented so he could release his pet poodle Gregory from itâs leash quickly. Among the other benefits he bought to the transport industry was the Bulldog clip for fixing number plates to the rear of trailers, and of course his most famous invention, The clip on tie, as commisioned by Eddie Stobart.
Harry Monk:
FWIW it says this on WikiâŚThe term âfifth wheelâ 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 horizontal wheel or segment of a wheel called a fifth wheel sometimes forms an extended support to prevent the carriage from tipping; it consists of two parts rotating on each other about the kingbolt above the fore axle and beneath the body
In which case then a drawbar trailer has a fifth wheel coupling just the same as a semi or a composite trailer. 
Carryfast:
Harry Monk:
FWIW it says this on WikiâŚThe term âfifth wheelâ 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 horizontal wheel or segment of a wheel called a fifth wheel sometimes forms an extended support to prevent the carriage from tipping; it consists of two parts rotating on each other about the kingbolt above the fore axle and beneath the body
In which case then a drawbar trailer has a fifth wheel coupling just the same as a semi or a composite trailer.
But more generally known as a turntable.
Fifth wheel coupling invented by a bloke called Big D from York
Wheel Nut:
Carryfast:
Harry Monk:
FWIW it says this on WikiâŚThe term âfifth wheelâ 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 horizontal wheel or segment of a wheel called a fifth wheel sometimes forms an extended support to prevent the carriage from tipping; it consists of two parts rotating on each other about the kingbolt above the fore axle and beneath the body
In which case then a drawbar trailer has a fifth wheel coupling just the same as a semi or a composite trailer.
But more generally known as a turntable.
Fifth wheel coupling invented by a bloke called Big D from York
Hopefully those birds in that office will be reading all this. But only the British could have invented a coupling used for artics in a country where rigids and/or drawbar outfits (with turntables) ruled .But some say that it was a bloke called Charles Martin who came up with the idea.
truckerjon:
I always thought that it was called a âfifthâ wheel because it was invented by Horatio charles edward Fifth, Inventor, (1893 - 1977). he is also credited with the dog clip, invented so he could release his pet poodle Gregory from itâs leash quickly. Among the other benefits he bought to the transport industry was the Bulldog clip for fixing number plates to the rear of trailers,
Given his choice of canine companion would he not have called it a Poodle Clip Instead of Bull Dog Clip. Unless Gregory had sadly been run over by a runaway 5th wheel and he had a new faithful friend by the time he started on his clip inventions?
Coffeeholic:
truckerjon:
I always thought that it was called a âfifthâ wheel because it was invented by Horatio charles edward Fifth, Inventor, (1893 - 1977). he is also credited with the dog clip, invented so he could release his pet poodle Gregory from itâs leash quickly. Among the other benefits he bought to the transport industry was the Bulldog clip for fixing number plates to the rear of trailers,Given his choice of canine companion would he not have called it a Poodle Clip Instead of Bull Dog Clip. Unless Gregory had sadly been run over by a runaway 5th wheel and he had a new faithful friend by the time he started on his clip inventions?
He did plan to call it the gregory clip, but someone had already used that name on a device for keeping a bishops mitre in place. He did want to call it a poodle clip, but fortuneatly was persuaded otherwise. Gregory did tragically die as a result of an electric shock from a pair of faulty curling tongues and, being British, Horatio got a pet bulldog called Nigel.
truckerjon:
Coffeeholic:
truckerjon:
I always thought that it was called a âfifthâ wheel because it was invented by Horatio charles edward Fifth, Inventor, (1893 - 1977). he is also credited with the dog clip, invented so he could release his pet poodle Gregory from itâs leash quickly. Among the other benefits he bought to the transport industry was the Bulldog clip for fixing number plates to the rear of trailers,Given his choice of canine companion would he not have called it a Poodle Clip Instead of Bull Dog Clip. Unless Gregory had sadly been run over by a runaway 5th wheel and he had a new faithful friend by the time he started on his clip inventions?
He did plan to call it the gregory clip, but someone had already used that name on a device for keeping a bishops mitre in place. He did want to call it a poodle clip, but fortuneatly was persuaded otherwise. Gregory did tragically die as a result of an electric shock from a pair of faulty curling tongues and, being British, Horatio got a pet bulldog called Nigel.
Thanks for clearing that up, Iâll sleep easy tonight now.
truckerjon:
Coffeeholic:
truckerjon:
I always thought that it was called a âfifthâ wheel because it was invented by Horatio charles edward Fifth, Inventor, (1893 - 1977). he is also credited with the dog clip, invented so he could release his pet poodle Gregory from itâs leash quickly. Among the other benefits he bought to the transport industry was the Bulldog clip for fixing number plates to the rear of trailers,Given his choice of canine companion would he not have called it a Poodle Clip Instead of Bull Dog Clip. Unless Gregory had sadly been run over by a runaway 5th wheel and he had a new faithful friend by the time he started on his clip inventions?
He did plan to call it the gregory clip, but someone had already used that name on a device for keeping a bishops mitre in place. He did want to call it a poodle clip, but fortuneatly was persuaded otherwise. Gregory did tragically die as a result of an electric shock from a pair of faulty curling tongues and, being British, Horatio got a pet bulldog called Nigel.
Some say that Nigel met itâs demise while trying to carry out a vicious attack on some fit looking birds in a transport office while his owner Horatio was demonstrating his new invention for attaching number plates to trailers.By all accounts those birds showed their gratitude afterwards to the lucky zb who rescued them from Nigel.But those birds swore ever since that it was a runaway fifth wheel not a bull dog which almost got them.
For whats its worthâŚ
Steve
neversweat1:
For whats its worthâŚ
Steve
Er, not much actually 
That is a description of an articulated vehicle, not a fifth wheel.
You will also note, it says âNot less than 20%â i.e. more than 20% is to be carried by the towing vehicle.
+1 for the 'osses 
A1ex:
neversweat1:
For whats its worthâŚ
Steve
Er, not much actually
That is a description of an articulated vehicle, not a fifth wheel.
You will also note, it says âNot less than 20%â i.e. more than 20% is to be carried by the towing vehicle.+1 for the 'osses
Itâs also a description of a composite trailer because a dolly has a semi trailer superimposed on it by using a fifth wheel coupling. But a horse cart and a drawbar trailer both use a turntable.Unless thereâs a horse cart somewhere with an artic fifth wheel coupling attached to the drawbar In which case it would be a composite trailer pulled by osses.
Carryfast:
A1ex:
neversweat1:
For whats its worthâŚ
Steve
Er, not much actually
That is a description of an articulated vehicle, not a fifth wheel.
You will also note, it says âNot less than 20%â i.e. more than 20% is to be carried by the towing vehicle.+1 for the 'osses
Itâs also a description of a composite trailer because a dolly has a semi trailer superimposed on it by using a fifth wheel coupling.
Unless it hasnâtâŚthen it isnât 
truckerjon:
Carryfast:
A1ex:
neversweat1:
For whats its worthâŚ
Steve
Er, not much actually
That is a description of an articulated vehicle, not a fifth wheel.
You will also note, it says âNot less than 20%â i.e. more than 20% is to be carried by the towing vehicle.+1 for the 'osses
Itâs also a description of a composite trailer because a dolly has a semi trailer superimposed on it by using a fifth wheel coupling.
Unless it hasnâtâŚthen it isnât
In which case itâs a drawbar trailer with a turntable pulled by osses. If you canât baffle em with bs blind em with science.
Eeh, you young uns know nowt. When I started driving there werenât many artics about. They were just starting to come into service and replacing rigids or wagon and drags. Virtually ALL the early artic units were four wheelers, (well OK six with the double wheels at back) one on each corner and the fifth wheel was the turntable. Most trailers were single axle. The maximum weights had not been changed and were the same as on rigid vehicles. We didnât have the advantages of 'Elf n safety regs. These came later. Because of this and the old fashioned regs most Artics at the time were limited to the same weight as rigid 6 wheelers.
The idea of 20% loading on the turntable may have come in later, (we didnât have it before decimalization and them Kilomometers) it probably came about because when the early artics were loaded if you didnât get the weight distribution right they tipped up when the unit pulled out when dropping trailers. The single axle at the back couldnât counterbalance a badly loaded trailer or a part loaded trailer if the weight was in front of the landing legs, so they altered the regs to protect you young uns.
I worked for Hanson Haulage and when we used to go out to load night trunk vehicles (artic vans) we had to load as much as possible upfront when out collecting and then back onto the loading docks in the depot to top up. Obviously you didnât want to be moving heavy stuff twice so it had to be loaded up to the headboard as much as possible. We used to shove a 45 gall drum and some planks of wood under the front of the trailer when the unit pulled part way out to stop it tipping. You canât report me for breaching 'Elf n safety rules cos they hadnât been thought of in those days. You young uns donât know how lucky you are.