5th Wheeler hitch

Hi everyone,
What advise can you provide re the fitting of a hitch in the twin cab for a 5th wheeler van? Some argue slightly forward of the rear axil and some say fitting to the rear is ok. Its all to do with towing stability and I am puzzled by the difference in option.

Bob.
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Reply By: Peter_n_Margaret - Thursday, Apr 17, 2014 at 15:04

Thursday, Apr 17, 2014 at 15:04
It is about stability.
Over or forward of the axle is inherently stable. The further behind the axle, the less stable.

Cheers,
Peter
OKA196 Motorhome
AnswerID: 530751

Follow Up By: Peter_n_Margaret - Thursday, Apr 17, 2014 at 15:07

Thursday, Apr 17, 2014 at 15:07
http://www.caravanandmotorhomebooks.com/articles/fifth-wheelers.html

Cheers,
Peter
OKA196 Motorhome
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FollowupID: 813704

Reply By: Iza B - Thursday, Apr 17, 2014 at 19:00

Thursday, Apr 17, 2014 at 19:00
Most knowledgeable people will say something like 50 mm forward of the centreline of the rear axle. You will not go wrong reading Peter's link. The Physics explain why stability becomes an issue as the distance rearward of the axle increases.

Iza
AnswerID: 530756

Reply By: Bob Y. - Qld - Thursday, Apr 17, 2014 at 21:22

Thursday, Apr 17, 2014 at 21:22
Bob,

Work on 2.5% of wheel base, in front of axle.

Bob

Seen it all, Done it all.
Can't remember most of it.

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AnswerID: 530763

Reply By: The Bantam - Thursday, Apr 17, 2014 at 22:34

Thursday, Apr 17, 2014 at 22:34
There are all sorts of opinions.

But if you want a good indication of sound articulated vehicle practice....look at the heavy transport vehicles.
They all have the turntable located pretty well directly over the centre of the rear axle or the rear axle group..

There are a number of advantages to this.

Staibility, correct loading of the tow vehicle suspenion.

But one many people don't grasp is a prodigeous advantage it gives in vehicle manovering.
The closer the hitch is to the centre of the rear axle, the easier the vehicle will be to manover.
A full blown semitrailer can be bent up past 90 deg and the trailer can be pivoted on its rear axle and driven a full circle....the ability of the rig to be bent up and have the tow vehicle follow the trailer arround almost any diameter circle..continuoulsy..is critical to what can be done with these rigs.

The manoverabilty that having the hitch directly over the centre of the rear axle gives will blow the mind of many who are used to rear hitch towing.

The problem with most twincab utes is you will not get a hitch directly over the rear axle, because it is almost under the back wall of the cab, and you will not get enough clearance to bend the rig right up.


In some countries it is common for the truntable to be adjusted fore and aft on the prim mover to maniplate the wheel loadings..In a uatralian turntables are mostly fixed.

Bear in mind that most utilities are designed to carry all the tray load on the rear wheels.....if you look at the single cab version of most uters the tray is centred over the rear wheels..this should give some insight into the loading design

Having the hitch located directly over the rear wheels or very close too is best...but not always achieveble.


cheers
AnswerID: 530771

Reply By: Slow one - Friday, Apr 18, 2014 at 07:46

Friday, Apr 18, 2014 at 07:46
Bob,

There really shouldn't be a difference of opinion. Turntables are normally mounted either centrally over the rear axle or foreword of it depending on the amount of weight you wish to have on the front axle. One good option is to have an adjustable slide turntable so it can be moved slightly foreword or aft.

Being a dual cab you will have to work out, how much weight you are putting on the front axle from gear you are storing in the cab. On your specification plate you should also be able to see what the max front axle weight is.

Moving the turntable slightly forward of the rear axle will do two things. It will spread the load more evenly and the vehicle will be more level.

My thought are around 1 or 2 inches forward of the axle centre point.

If you can find a bunch of prime movers like in a truck sales yard, you will see how many are different in the turntable positioning.
AnswerID: 530778

Follow Up By: The Bantam - Friday, Apr 18, 2014 at 09:31

Friday, Apr 18, 2014 at 09:31
I find it interesting that people are giving specific advice about where to locate the turntable including specific measurements when we have no idea what vehicle the OP has or the load they are trying to carry.

Of course the turn table locations will vary a little on heavy prime movers..because there is a great deal of difference in the chassis lengths and arrangements, the axle loadings, the number of axles, the axle locations on the chassis, the type of suspension and to a certain extent the load carried.

But it would be very rare indeed to find a heavy truck with the turntable located behind the centre line of the rear axle group.

But it seems common on fifth wheel caravans, particularly those towed by dual cab utes.

The detail of this discussion is realy one for a transport engineer...dealing with specifics.

cheers
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FollowupID: 813751

Follow Up By: Slow one - Friday, Apr 18, 2014 at 10:46

Friday, Apr 18, 2014 at 10:46
Well, Well. I find it interesting that I even bothered replying.

1. Read what I wrote about the vehicle and loading. The best place to start is with the turntable pivot point over the centre of the rear axle. Now if you can adjust the turntable as I stated you can move it forward too get the best position, 1 or 2 inches. Read what I STATED about load carried in the cab and front axle loading, open your eyes.

2. Primemovers. Looks like you can mention them and I can't. The example of a prime mover is just that, it will give the OP a perspective on how much of a difference turntables are mounted on heavy vehicles, and thanks for explaining about wheelbase, suspension and axles, I would never known about that. I must ask my mate I drive for about it.

3. Did I say ANYTHING about mounting the turntable behind the rear axle.

Nuff, said or again the OP will get a chook headache.
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FollowupID: 813758

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