Sway control for light caravan

Submitted: Saturday, Jan 02, 2016 at 16:05
ThreadID: 131255 Views:2336 Replies:5 FollowUps:4
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Some of you may recall my "ultra light caravan build" in these pages. I'm nearly finished the van.

Some obstacles needed to be overcome. The van was to have a tare weight of a mere 200 kgms but will be more like 220-230 kgms upon completion. This low low weight is due to the tow vehicle being a VW rear engine style trike. Too much weight and the front wheel wants to lift and so on.

Hence my design was to make the van close to neutral in its balance. And....better to make the van even a little tail heavy initially then use weight (battery, tools etc) up front or in a toolbox on the front of the drawbar than climbing over items at the rear of the van everytime you stop. ADR's are adhered to with 20mm more distance axle to front loading area compared to axle to rear of van.

This unique situation has brought some concerns. One reader here raised the concern of van sway especially with semi trailers passing by. So have seen some anti sway devices but they are usually for towball weights exceeding 160kgms.

This unit here is from 0 kgms upwards. I was wondering if anyone here has used one or what your opinions are.

Sorry for the ramble but had to explain it all as its an unusual build.

ps...the towball maximum weight for this trike is 25 kgms.


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Reply By: eaglefree - Saturday, Jan 02, 2016 at 16:32

Saturday, Jan 02, 2016 at 16:32
Also, I see you cant reverse with these units attached. Sounds like very inconvenient??
AnswerID: 594403

Reply By: The Bantam - Saturday, Jan 02, 2016 at 18:38

Saturday, Jan 02, 2016 at 18:38
When you speak to "caravan people", many of them can't believe that other trailer formats do not have sway problems.

Years ago I had a bloke, talk to me like I was an idiot because I did not have some sort of weight distributing hitch on a 1 tonne box trailer ,and he ranted that I needed to have at least 100Kg ball weight.

It must be understood that part of the problem is that the single axle trailer is a fundamentally unstable format .... and the taller, longer and higher the unit gets, the worse the stability problems get.
It gets even worse when weight is concentrated at the ends of the caravan ... as it is in some designes.

It also follows that the shorter and more centrally loaded the trailer is the less unstable it will be.

So someone towing a short, low brick of a trailer will probably experience none of the problems that terrify many caravan owners.

I have no problem keeping the ball weight low .... but on your trailer .hell 10% or 20Kg is not going to be a problem.

What I would strongly recommend is keeping as much of your weight as low and centrally located as possible ....... this with promote stability and as that weight ( like water tanks) changes, the behaviour of the trailer will change less.

One other reason for stability problems with caravans towed by passenger cars is ..... the passenger car squirms under the load of the caravan, because it is a passenger car and the suspension is designed to be soft and baggy and there is mostly a long distance between the hitch and the centre of the rear axle ..... squirming and a long lever..... this squirming excites the instability in the trailer.

Ya probaly wont have that problem either.

One thing I strongly recommend is shock absorbers on the trailer.

I remain gob smacked that many big expensive caravans have no shock adsorbers. so they have nothing stopping the trailer once excited from hopping from one wheel to the other,

The one thing that would realy concern me is such a light van is windage ..... you may have problems in crosswinds and with passing trucks ..... all the more reason to keep ya weight low.

OH and remember ..... in heavy transport, weight distributing hitches and anti-sway devices do not exist. ...... these devices are a patch up to correct a specific problem of a fundamentaly unstable combination.

AnswerID: 594409

Reply By: eaglefree - Saturday, Jan 02, 2016 at 18:59

Saturday, Jan 02, 2016 at 18:59
Thanks Bantam, your explanation made a lot of sense.
Yes, the low CofG of heavy items was planned in the design. The 44 litre water tank runs 60mm from the axle, the Waeco CF-18 fridge has its mount the same on the passenger side and to balance, the toilet/shower with its acrylic walls is on the other side. There's heaps of storage space under the single beds and so far a vacant drawbar so the options of balance are many.

Windage - well a close watch on weather via google is a must. Eyelets on the peak of both exterior walls will tie the van down in windy conditions.

Electric brakes weren't in the design. Now they are, in the near future. Set up so they come on with the trikes brake light and the actual trikes brakes coming on slightly later will give me some confidence to straighten up when in a messy situation.

Thanks again.
AnswerID: 594410

Reply By: noggins - Saturday, Jan 02, 2016 at 23:52

Saturday, Jan 02, 2016 at 23:52
The ''sway control'' you've posted is ideal for your situation.
You can set the tension to as tight as you need it, I use one on my Caravan and it took out the " big rig passing suck in" that you sometimes get.
As for not using it when backing up
Why didn't someone tell me that .
I never take mine off till i"m ready to disconnect and set up site.
If you set it up so it will allow a full jackknife with out bottoming out , or pulling out , no worries.

As for lift when too heavy on the back see if you can get the hitch below the axle height.

"Think about it "

The pull is down slightly on load but will lift on heavy braking so have the Van brakes set aggressively

AnswerID: 594425

Reply By: 671 - Sunday, Jan 03, 2016 at 12:37

Sunday, Jan 03, 2016 at 12:37
There is a fair chance it will get blown around with that light weight combined with all of that wind catching side surface area. I would imagine the anti sway device would have to help but another just as important thing is the suspension design. Have you set it up to progressively increase roll understeer as the van leans while swaying? Cars are designed to do that to aid stability but caravans with their short stiff leaf springs or trailing arm independent suspensions all attached under a flat chassis create roll oversteeer which definitely does not help.
AnswerID: 594442

Follow Up By: eaglefree - Sunday, Jan 03, 2016 at 14:48

Sunday, Jan 03, 2016 at 14:48
thanks 671.

The suspension design is stock box trailer springs- 3 leaf. The only thing helping being the 71 inch axle.

I think you are talking about a sway bar as they called them in the 70's and I purchased one for my Valiant them days aftermarket that bolted straight onto the existing sway bar a the time to "stiffen" it all up so us young guys could corner faster.

It's obvious to me that sway and fishtailing are two different things. Sway is rocking from side to side and fishtailing is obviously movement that is quite different. Hence a sway bar would be more along the lines of fitting the need. Fitted correctly a sway bar wouldn't effect up and down suspension and one could be sort from a wrecker.

Thanks for the tip. Hadnt thought of that.

FollowupID: 862824

Follow Up By: 671 - Sunday, Jan 03, 2016 at 22:07

Sunday, Jan 03, 2016 at 22:07

I am not talking about sway bars. Have a look at your trailer springs then compare them to a car with leaf springs. The trailer will have a short spring with a fair size arc in them. The shackles will be at the same height.

A car will have a much longer and flatter spring. The front spring eye will be mounted much lower than the rear eye. The axle will be placed further to the front end of the spring than the rear end. When the car is nearing full load, the front section of the spring will be either parallel to the ground or sloping up to the axle. As the car leans into a corner, the spring will go into a concave shape and the axle will get closer to the chassis. This swings it up in an arc around the front shackle bolt and takes the wheel closer to the front of the car. The wheel on the other side will be dropping down and moving back. The axle will now be pointing slightly in the same direction as the front wheels. That is roll understeer. It assists in vehicle stability and is the reason why car and ute leaf springs are made long and fairly flat and mounted with the front lower than the rear.

They don't go flat when loaded and concave in corners because the car manufacturer does not know how to make a good suspension like many people with overloaded rear end sagging cars seem to think. They have been designed that way.

Now go back to your trailer suspension and you will soon see that it can not possibly give the same result. In order to pull the outside wheel slightly forward in a corner, the axle has to get up higher than the front mounting point for the spring. That is impossible with a flat chassis. All the spring can do is flatten slightly and push the wheel back. The other side will drop down and pull its wheel forward. You now have the axle pointing in the opposite direction to the front wheels and that is not real good.

Fishtailing and swaying (yaw or leaning) go together. Have you ever seen a fishtailing caravan remaining perfectly upright while it swings from side to side?

I don't know how your little van is going to behave but if it does get knocked about by high wind or passing trucks then it is going to move to one side and lean over then whip back and maybe go too far the other way. That is when a car like suspension design could be a priceless advantage.
FollowupID: 862845

Follow Up By: eaglefree - Sunday, Jan 03, 2016 at 23:04

Sunday, Jan 03, 2016 at 23:04
Thanks for that. Such clarification.

Certainly I'm now armed with really good information once the van is on the road.

I've even printed this thread out.
FollowupID: 862846

Follow Up By: Member - John - Monday, Jan 04, 2016 at 01:08

Monday, Jan 04, 2016 at 01:08
G'day, exactly why my camper trailer with Hilux rear springs tracks so well.................
John and Jan

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FollowupID: 862847

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