Fifth wheeler

Submitted: Saturday, Oct 12, 2013 at 18:05
ThreadID: 104694 Views:4012 Replies:7 FollowUps:12
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Hello all,

From a engineering / design view, at what length would you choose a 5th wheeler instead of a caravan?

Thanks
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Reply By: The Bantam - Saturday, Oct 12, 2013 at 19:56

Saturday, Oct 12, 2013 at 19:56
In every case a fifth wheel combination will be more stable and easier to drive than a rear hitched caravan.

The fifth wheel places the load within the vehicles wheel base and not as a pendulum hanging off its rear extremity.

It also places the hitch point near the centre of the rear axle of the tow vehicle making it very much easier to manover and giving a way tighter combination turning circle.

I would have an articulated combination ( fifth wheeler) over a "pig trailer" in every case where one was available.

There are very good reasons why articulated combinations and dog trailers greatly out number pig trailers in heavy transport.

cheers
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Follow Up By: Member - Peter H1 (NSW) - Sunday, Oct 13, 2013 at 07:54

Sunday, Oct 13, 2013 at 07:54
I agree 5'er's are much easier to handle.

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Follow Up By: wombat100 - Sunday, Oct 13, 2013 at 18:33

Sunday, Oct 13, 2013 at 18:33
Not quite right Bantam..
If the turntable is 'behind' the axle it's a 5th wheeler
If the turntable is ahead of the axle it's an articulated vehicle (ie. a semi-trailer)...

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FollowupID: 799833

Follow Up By: hazo - Sunday, Oct 13, 2013 at 18:52

Sunday, Oct 13, 2013 at 18:52
Sorry Wombat, but totally wrong. This has been done to death on the caravan forums and a 5th wheeler is and always classed as a car and caravan immaterial where the hitch is fitted.
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Follow Up By: wombat100 - Monday, Oct 14, 2013 at 10:32

Monday, Oct 14, 2013 at 10:32
Hiya Hazo
I'm not an expect on this subject.
Only going on what my local RTA office tells me.
Cheers

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Follow Up By: Ron N - Monday, Oct 14, 2013 at 12:02

Monday, Oct 14, 2013 at 12:02
The turntable can be either in front of the tow vehicle rear axle, right on top of it, or behind it - and the setup is still classed as a 5th wheeler.

http://www.towingguide.com.au/content/wheeler%20_towing.html

The important thing is to realise what happens with tow vehicle loading with a 5th wheeler.

Turntable behind the rear axle - rear axle loading is increased and front axle loading is reduced.

Turntable on top of rear axle - all of the vans turntable weight is applied to the rear axle and the front axle loading is unaltered.

Turntable in front of the rear axle - the vans turntable weight becomes shared between front and rear axles, in accordance with the distance forward of the front axle.

It's just as critical with a 5th wheeler, as it is with a towball-hitch van, to ensure that the tow vehicles manufacturers rear axle load rating, and the rear tyre load rating, isn't exceeded.

It's also important to ensure that the weight carried by a 5th wheeler vans wheels does not exceed the tow vehicles, manufacturer-rated, trailer-towing capacity.

Now, here comes another couple of points, that many don't think of.

It's very easy to exceed 4.5 tonnes gross weight with a 5th wheeler. Over 4.5 tonnes GCM or GVM, you need a truck licence!

And - you cannot drive a 5th wheeler on a car licence in the ACT!

In the ACT a 5th wheeler is deemed an articulated vehicle and an articulated (HC class) licence is required!

http://www.rego.act.gov.au/assets/PDFs/5th%20wheeler%20handout.pdf
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FollowupID: 799868

Follow Up By: The Bantam - Monday, Oct 14, 2013 at 12:45

Monday, Oct 14, 2013 at 12:45
In the current regulatory system Articulation is pretty well, no longer a factor in either regestration or licencing.....just about everything is assessed bassed on mass alone.

As far as the definition....it comes from heavy transport and the term "Fifth wheel trailer" that refeers to the turntable used in heavy transport is not commonly used in Australia.

Overseas it is common to "adjust" the fifth wheel, moving the turntable back and forth to manipulate the load on the prime mover....that too is not common in Australia, most prime movers have turntables in fixed positions....they do all sorts of weird stuff overseas

This use of the term "Fifth wheeler" comes from America and realy only seems to be used in relationship to caravans in this country.

If you where in the horse or livestock community, you are more likely to refeer to an articulated trailer as a goosekneck trailer

The fact remains there are 3 basic types of trailers permitted on Australian roads.

The pig trailer...a rigid drawbar trailer with a single axle group like most box trailers and the majority of caravans.....considered a poor choice in heavy transport because of its inherant instability...they are a pig of a thing.

The dog trailer....a self steering trailer that has an axle group front and rear and carries itt whole weight on its own wheels.....called such because it follows around like a well trained dog.

and

Articulated trailers.....this is the group that contains semi trailers, fifth wheel trailers, gooskneck trailers or what ever else you want to call it.

If ya doubt me check out VSB 14.

Even more confusing a lot of the time the articulated trailer has no turntable and is hitched using a ball....thus there is no fifth wheel.....but people still persist in calling them "Fifth wheelers"

Where the hitch point is in relation to the rear axle, is a design matter and determines how the load from the trailer hitch is shared on the tow vehicles front and rear axles.

BUT almost without exception the hitch is close to the centre of the rear axle......sometimes maybe forward of it sometimes to the rear of it.......but it is not placing the drawbar load way out beyond the rear of the vehicle on a lever that tends to place more load than borne on the ball on the rear suspension and lift the front suspension.

One significant advantage of an articulated combination (or what ever else you want to call it), is that it is possible to place a lot more of the trailer weight on the tow vehicle than would be permitted rear hitched.

SO on a light vehicle (say a light truck) with a passenger car licence limit of 4.5 tonnes GVM, it may well be possible to tow a trailer that actually weighs 5.5 tonnes ATM. a full tonne borne on the tow vehicle.

Ball weights written for rear hitched towing do not apply and it is reasonable to put 30% or more of the trailer mass on the tow vehicle.

The other big advantage of articulated towing is, when properly designed the addition of hitch down force does not tend to take weight off the front wheels of the tow vehicle....in fact it may place more down force on the front wheels making steering and front wheel traction more reliable.

Articulated towing is by far the most stable and most civilised towing arrangement available that is why it predominates in heavy transport.

We are even finding Coca Cola now running single axle semi-trailers towed by medium rigid primemovers in preference to rigid trucks.
because that are more manoverable......and they can be driven on a medium rigid licence.

cheers
1
FollowupID: 799870

Follow Up By: The Bantam - Monday, Oct 14, 2013 at 14:13

Monday, Oct 14, 2013 at 14:13
Just to clarify.
If you go and look at licence conditions you will see that the permitted towing allowance is based on GVM..that is the mass borne by the wheels of the trailer.

The limits for the vehice driven are specified based on GVM and the towed trailer permitted in GVM..and that is right across the board from pasenger car licences up.

Articulation is no longer a licencing issue.
Under the previous arrangement, you could drive a 25 tonne truck towing a 20 tonne dog on a truck licence, but you could not drive a 10 GVM tonne prime mover towing a 9 tonne ATM articulated trailer, that required an articulated licence.
Now the truck and dog require a heavy combination and the little semitrailer requires only a medium rigid.

I believe that to be the case nationwide.

cheers
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FollowupID: 799879

Follow Up By: Nomadic Navara - Monday, Oct 14, 2013 at 16:22

Monday, Oct 14, 2013 at 16:22
Goose neck is not a term used in legislation. It's just a colloquial term.

From FollowUp 6 - "If ya doubt me check out VSB 14."

Vehicle Standards Bulletin 14 (VSB 14) is not a single document. Which of its components are you referring to? If you are quoting definitions you should referr to Vehicle Standard (Australian Design Rule Definitions and Vehicle Categories) 2005 Compilation 6

There are two definitions there of note.

FIFTH WHEEL ASSEMBLY - a ‘Fifth Wheel Coupling’ including any turn-table,
mounting plate, sliding assembly, load cell and other equipment mounted between
the towing vehicle chassis and the trailer ‘Skid Plate’, but not including any
‘Attachment Sections’.

FIFTH WHEEL COUPLING - a device, other than the ‘Skid Plate’ and the kingpin
(which are parts of a ‘Semi-Trailer’), used with a ‘Prime Mover’, ‘Semi-Trailer’
or a ‘Converter Dolly’ to permit quick coupling and uncoupling and to provide for
articulation.

There is no definition that refers to 5th wheel trailer so I take it that is also a colloquial term. Most of the common conversations (verbal and written) seem to refer to the term 5th wheeler to cover all semi trailer type vans and goose neck as a subset with a ball coupling.
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Follow Up By: Ron N - Monday, Oct 14, 2013 at 19:48

Monday, Oct 14, 2013 at 19:48
Nomadic Navara - Yes, it's interesting, isn't it? Everyone knows what a gooseneck trailer is, thousands are on the roads - yet they're never mentioned in any legislation.
However, State VSB's frequently refer to low-loader trailers, as "goose neck style trailers"!

http://www.rms.nsw.gov.au/registration/downloads/vsi/vsi5.pdf

The horsey set use 5th wheelers and goosenecks on a huge basis - Exiss alone, have sold 100, imported American 5th wheel horse trailers, just in the last year alone!

Yet the authorities can't seem to get their little legislative brains around any descriptions, rules or nationwide regulations for RV style, and horse float style, 5th wheelers and gooseneck design trailers!
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Follow Up By: The Bantam - Monday, Oct 14, 2013 at 21:07

Monday, Oct 14, 2013 at 21:07
I refeered to VSB14 because it is the most convienient summary on the matter of light trailers.....and yes that is what it is, a summary, on its own it holds no legal status... the legal weight is in the legeslation, ADRs and standards that it points to.......but it is a reasonable summary and contains most of what people need to know.

In the reasonable summary there are diagrames (lifted from the ADRs) showing the types of trailers and how they are classified and what they are called.

both " fifth wheel trailer" and "goosekneck trailer" seem to be coloquial terms and not consistently used.

AND the prevalence of their use varies depending on context....."fifth wheeler" seems to be more prevalent in the Caravan communitiy and "gooskneck" seems to be more common in the livestock community and it seems not to matter what sort of articulated trailer or coupling is the subject.

While the term "fifth wheel" may be mentioned in standards and legeslation the term is hardly mentioned in the heavy transport industry.

The term "turntable" is almost universal.

Persoanally I believe the term "Articuculated trailer" should be used, because that is what they are called in the official documents, that is what they are and it is clear what is being referred to.

I find it curious that some people seem to see fit to name a trailer by its coupling arrangement rather that its relationship to the towing vehicle.

while there are only two main coupling types that prevail in articulated trailers, I am sure someone could invent a different type of coupling...would we then start naming that trailer by this new coupling type.

we have not named a whole heap of off road trailers as swiveling pin coupling trailers or others as ring coupling trailers or the remainder ball coupling trailers.....they are trailer that happen to have whatever coupling.........so why should we do something similar to articulated trailers.

I don't call my 4 wheel drive a "4 wheeler" as many do, because most small vehicles have 4 wheels.
So why should we call an articulated caravan a fifth wheeler, particularly if it may be coupled by a ball.


cheers
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Reply By: Iza B - Sunday, Oct 13, 2013 at 08:03

Sunday, Oct 13, 2013 at 08:03
Many a knowledgeable commentator has suggested that stability issues come in at the 14 foot mark for a caravan. Any van over about 15 foot should really have dual axles but an 18 foot fiver can get away with a single axle/pair of wheels because the tug carries a portion of the weight. You can also build a fiver chassis that is stronger and stiffer and lighter than an equivalent living length caravan. There are lots of other considerations, such as combined length, but I think a big one is that internal layout is easier in a fiver.

I am biased because I could not find any van small enough and light enough so I'm in the early stages of an 18 foot, single axle fiver.

Iza
AnswerID: 519625

Reply By: Member - Wamuranman - Sunday, Oct 13, 2013 at 08:04

Sunday, Oct 13, 2013 at 08:04
I agree with the engineering logic described above. Our off-road van is 21ft 6in and has a full ensuite, queen size island bed, plus dinette. Without the ensuite being squashy (includes a washing machine) I believe 21ft 6in is the "shortest" that combination will fit comfortably. If for some reason I wanted to go significantly bigger I would start to look at 5th wheelers - personally over 23ft would be the trigger point for me. We can tow our van confortable at 100kph on good roads but it is well built with independent suspension and tracks very well. All vans are different. But it makes sense to go 5th wheeler to me if I wanted to go bigger (which we don't at this stage). Cheers
AnswerID: 519626

Reply By: Ron N - Sunday, Oct 13, 2013 at 13:01

Sunday, Oct 13, 2013 at 13:01
I owned several 26 and 28 foot tri-axle Viscounts - and in the early days, a 30 foot Modern that was only single axle! It was fitted with Landrover hubs and wheels. All these vans towed well, and I never had a problem with any of them.

I towed the Modern (which weighed 2.8 tonnes) with a Series II petrol traytop Landrover. The Landrover peaked out at about 85kmh with the Modern, but the Modern always towed beautifully - as did the Viscounts. It's all about how you set up your van.
The choice between a regular van or 5th wheeler, to me, is more about personal choices of design, than size.

A 5th wheeler means a dedicated tow vehicle and van, unlike a regular van which can be towed by any suitable vehicle with a towbar.
A 5th wheeler does offer a greater degree of towing stability, for sure, but usually at greater cost as well.
AnswerID: 519643

Follow Up By: The Bantam - Sunday, Oct 13, 2013 at 19:07

Sunday, Oct 13, 2013 at 19:07
For most people any large van means a dedicated tow vehicle.

Sure you may find a 50mm tow ball on the back of lots of vehicles.

But you have to deal with the various ratings, have the appropiate brake and power systems installed.
That vehicle has to have the appropriate fittings for the stability gadgets.

That suitable vehicle may not be all that easy to come by.

Then we look at all the gadgets that are more or less de-rigour to deal with the inherant stability issues of pig trailers towed by passenger cars.

Another big advantage of an articulated combination is that you don't have the issues of a low mounted drawbar and all the ramp over, and dip thru issues that plague every rear towed caravan.

There are plenty of articulated tow vehicles that remain usefull and functional with a turntable or ball in the back.

Lots of horsey types still go an pick up feed and stuff with the same ute or truck they tow their goosekneck horse float with.

There are even those who either remove the coupling when not in use...an interesting idea.....and some have lift off bodies that drop straight on over whatever coupling is there.

all things worth considering.

cheers
1
FollowupID: 799836

Follow Up By: Iza B - Monday, Oct 14, 2013 at 06:48

Monday, Oct 14, 2013 at 06:48
A fiver does not need a dedicated vehicle to tow it. I can remove the ball at will and use the tray whenever I want.

Iza
1
FollowupID: 799855

Reply By: Gunbarrel Greg - Sunday, Oct 13, 2013 at 17:23

Sunday, Oct 13, 2013 at 17:23
Hello all,

Many thanks for the advice and opinions given. Safe travels to you all.
AnswerID: 519650

Reply By: Lyn W3 - Sunday, Oct 13, 2013 at 20:55

Sunday, Oct 13, 2013 at 20:55
Here is the correct explanation.

5th Wheel and Gooseneck trailers
AnswerID: 519658

Reply By: Ron N - Monday, Oct 14, 2013 at 13:30

Monday, Oct 14, 2013 at 13:30
Greg - Here's more food for thought. Not enough people are aware of the variations in the types of 5th wheel hitches, and their limitiations.

There are three styles of 5th wheel hitch - single pivot, double pivot and gooseneck ball hitch.

A large number of 5th wheel hitches are of the single pivot style. One has to be aware that this style of hitch does not allow for very much twisting action (longitudinally) between the tow vehicle and the van.

A single pivot hitch is designed for use on smooth, flat road surfaces. Using this style of hitch in conditions where there is substantial amounts of longitudinal twisting (as in off-road conditions, or hilly area driveways), means that substantial twisting forces are applied to the van frame - often resulting in frame cracking and other damage.

A double pivot hitch and a gooseneck ball hitch allows substantial longitudinal twisting action between tow vehicle and van that eliminates twisting forces being applied to the van frame.

A single pivot hitch does offer an increase in cornering stability as compared to a double pivot hitch, or a gooseneck ball hitch.
Simply put, a single pivot hitch has 4 points of van support, whereas a single pivot hitch and gooseneck hitch have 3 points of support.

This "cornering support" angle mostly comes into play with a van with a high C of G.

http://www.youtube.com/watch?v=RqY2jFfkcRA

http://www.cutlooserv.com.au/tow-vehicles-tow-mass-guide.php

http://www.exploroz.com/Vehicle/Caravans/FifthWheelCaravans.aspx

http://www.exploroz.com/Vehicle/Caravans/Caravan_Dynamics.aspx

AnswerID: 519683

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