Weight Distribution Hitch

Thanks Ross M

I measured the ride height at front guard of the mazda which was 840mm and the rear was 892mm. When i hooked up the van the front measurement was 860mm and the rear was 840mm. I fitted heavy duty shocks to help control the bounce..

The van wants to start swaying at about 95kph. Its not be bad when both water tanks are full. I thought by using the intermediate hitch it could take some weight off the towbar and maybe stop the swaying and the bouncing action. I also thought the intermediate hitch would put less stress on the tow bar??

Wayne

Wayne,
Any hitch will be working the towbar to the max as all the forces that are transferred to the chassis and the forcing down of the front wheels of the tow vehicle are done by trying to twist the square section of the tow bar vis the hitch.
I don't know the relative measurements of guard hieght as I don't look there to set a vehicle.
I always look at the, axle tube to bump rubber distance, as it is this measurment which works or doesn't work for you.
Good shockers as you have fitted is OK but they can't get much time to act if the distance of the said axle to bump rubber clearance is small.

What yopu are trying to achieve is a distance of travel which will allow the compliant action of the suspension to absorb the movement and effectively cushion everything.
If is starts to sway at 95kmh I would look at the tyre pressures you are running, the type of tyres on the van and also the loading of the van.

Many hitches increase the distance of the ball from the rear axle and this is something which should be kept to an absolute minimum to stop the van taking steering control away from YOU.
Most hitches, all I have seen , incease this distance, making it more unstable and also harder for the suspension to control the pitching of the van, purely because it is further away from the rear axle. Also worse for chassis which is transferring the forces.

Does the tongue of your towbar stick out with it's Ball Bracket away from the square receiver of the towbar.
Many do stick out and are stupidly supplied by the "Fitting Porfessionals", to customers like this. Redrilling the towpin hole, I have altered many, might bring your tongue closer to the vehicle and begin to make the situation better for load carrying, steering/stability and ride control.

Ah, the joys of towing.

Ross M

If your van wants to start swaying at 95kmh, then you usually have a major problem associated with weight distribution in the van. Look towards moving heavy, dense, moveable items from behind the axle/s to towards the front, and at least as far forward as the axle centre.
You may also have excessive weight up top - and this coupled with minimal-ply-rating tyres, and too-low tyre pressure, will exacerbate the top-heavy problem. Heavy crockery and household items should be carried low in the van, lightweight stuff up top. A van should tow without sway at 110kmh.
Any tendency to sway is an invitation to disaster, that will happen in an instant - such as a van-body truck passing you too closely at high speed, and the wind blast jerking the van, and starting a tailwag that is difficult to regain control of.

Ross, have you weighed your van? What is its laden weight and the ball weight? The ball weight should be around 10% of your laden weight. If it's not then that could explain the sway problems. You need to get the sway problem sorted out, WDH is not for getting sway problems sorted out.

Forget all the misinformation about beefing up the rear suspension to carry the ball load. WDH is used to to replace the weight removed from your front suspension when you hitch a van. When you adjust the WDH properly you will find the front and rear wheel arches will both be lower than before you hitched the van as you will have the vans ball weight loaded equally to both axles. In other words with equal weight on both axles the tug will be back level again. If you need beefed up suspension it's because you have too much load in the back of your vehicle.

WDH is essential to restore your steering and braking performance to your front wheels when the van is hitched up.

The only sure way of determining which WDH you need is to weigh your ball weight. You then select the model where the ball weight falls within the specified weight limits of the particular WDH model. In your case the lighter model will probably be too light for your vans ball weight. A WDH that is too light for your van is not capable of distributing the ball weight equally over both axles.

G'day Nomadic Navara
I think youhave your Waynes and Ross's mixed up.
It is me replying to WAYNE.
I don't have the said problem at all.

Ross, you are correct. That's what happens yhen you are posting just before bed time. I perhaps should not have addressed the remarks to anyone, should have just addressed it to everyone.

Thanks for your helps Guys

Ross M I will try your suggestion on the weekend if I get time, The van is only running 34psi in it tyres, i'm going to try 46 to 50 psi on the weekend the tyre will handle 50psi OK they are Firestone 235/75 AT .

I alread have heavy duty torsion bars and spring packs coming. Hopefully the tyre pressures and a heavier ball weight may fix the problem.

The van has shockabsorbers on its suspension (single axle)

Thanks again for your help guys I will let you know how i go

Regards
Wayne

If you have a heavy van and a WDH and air bags they will work, I like air bags but they don't distribute the weight, only carry it. They act the same as having srings acting at a higher level eg more weight carrying ability.

The natural leverage of the van will still nose up the tug even with better springs or airbags.
Unfortunately airbags act in the middle between where the spring naturally takes the weight.
Therefore, they are forcing the chassis upward midway between the spring anchor points. Yes they do work, and I have used them too, but they can crack the chassis by having them at too high a pressure and relying on them instead of having capable springs in the first place.
Also airbags are not linear in the way they absorb weight and develop increasing resistance to upward travel particularly if too high a pressure is used.
Airbags, when compressed fully are no good at absorbing the sudden impact of a fully closed up suspension and because of their closed thickness actually reduce the full upward travel of the suspension.
As said, capable springs in the first place begins to address the problem.

Jayco caravans latest ball weight figures are nowhere near the 10% which people blindly follow as a rule. They seem to be around 7% or 8%.

It does seem as loading or tyres is a troubling factor here though.
I wonder if Wayne has shockers on the van cos if it hasn't then the wobbles will most likely occur.

Ross M

Hi GT Campers

I was told by a caravan centre i would need WDH as safety precautions and 95% of vans use them.

I would prefer to get the balance right so i didn't have to use WDH. As i feel they could put add stress on the tow bar and chassis.

I want to start by checking the simple thing first, like ball weight, suspension, load, tyres etc and the last resort is WDH.

Vans is a off road single axle jayco GVM(1800kg) the suspension i fitted with shock absorbers.

The van is load with heavy items near floor, only one spare wheel is mounted on rear bumper bar.

It has 150kg on ball with water tanks empty. Tows better with full water tanks give it more ball weight. I think a heavier ball weight may help, as it has a 20litre jerry can holder on the A frame but i haven't towed it will a full jerry can yet.

The van layout is front Kitchen Lounge Bed at rear.

I will do the thing Ross M has suggestedon the weekend (Thanks Ross) the tyre on the van a firestone 235/75 AT. I will pump them up to 46psi as they only have 34psi in them now and then try it. I could even try put more air in the bravos tyres it has 265/70 AT Michelin.

The van looks level . Hopefull the tyre pressure may fix the problem as i can easily rock the van side ways with 34 psi in them. What pressure would you recommend i put in van and mazdas tyres?

Hi RonN
Thanks for your reply
I have a heavy duty suspension coming for the mazda.
I would prefer to fix the problem to Ron instead of using the WDH as the bandaid..

The information i have gained from this forum is pointing to tyre pressure and ball weight.

The van is a poptop 16.5feet jayco discovery outback the largest you can get on a single axle.
Tyres are Firestone AT 235/75 but only have 34psi in them..
Suspension is fitted with shock absorbers
GCM 1800kg Ball weigh 150 kgs with empty waters (2)
Van design Front kitchen Loung Bed at rear not much i can do about the layout (LOL)
Only have one spare tyre on rear bumper no boxes fitted.
What tyre pressure would you run?

regards
Wayne

G'day Wayne - Well, the tyres should have a maximum inflation pressure listed on them. You don't say what they are load rated at, but I'd expect that at 900kg a tyre, this is approaching their maximum load capacity, so you need to carry pressures consistent with a full load.
I would go to 38 or 40 psi to see if there's any improvement, but I don't think you should go over about 45 psi, or you could end up with the tyres wearing excessively in the centre of the tread.

Most certainly don't exceed the tyre manufacturers maximum pressure recommendations. A tyre with excessive pressure in it, is more likely to fracture from stone or other hard object impacts.

150 kg towball weight should be an adequate weight for satisfactory handling, although 180 kg is probably better, if this is within the towbar rating.
One has to keep in mind any load you're adding to the Mazda, too - as a 180kg towball weight is the equivalent of already having about 360 kg in the tray.

I would say the Michelins on your Mazda could be a contributory factor in the sway, and these probably need inflating more.

The Michelins are a good tyre, but they have a very soft wall, and they wallow a lot. I'd try inflating the Michelins up to around 45 psi to see if there's any improvement in the caravan handling.
The Michelins don't mind higher pressures. I've used a lot of Michelins since the mid-1960's, and I've alway kept the pressures up in them.

The van is a good size for the Mazda, I can't see any major problems in the design, in what you describe. A single axle on a 16.5 foot van is quite O.K.
Perhaps, being an outback model, and having higher ground clearance, that's increased the C of G to a level that makes it not as good to tow as a standard van.

The only thing that I can see, is that the van weight is pretty hefty for a 16.5 foot van, and this is possibly running the van tyres to near their load limit.
If you can't gain any measureable improvement in handling with any of the above suggestions, you may want to change the Firestones to a heavier load rating tyre.

Cheers - Ron.

Wayne.
Option #2
A WDH is not a bandaid, but a tool to distrubute weight back to the front axle so that steering and braking are not compromised.
Nothing other than a WDH can carry out this important safety function.
Cheers, Ozjohn.