Weight distribution hitches — what do they really do?

I first used a weight distribution hitch when I borrowed my father-in-law’s caravan 30 years ago. To be completely honest, I didn’t have a clue what it did, and I found it a little bit scary because of the obvious spring tension imparted when you ‘crank up’ the system. I suspect I am not the only one to have this perception of these often misunderstood devices.
Fortunately, I have a fair bit more caravanning under my belt now and the luxury of drawing on the knowledge of some genuine industry experts on the subject. Rather than describe how to use one, here we have a crack at explaining what happens to help you decide if a weight distribution hitch is right for you. It gets a bit technical so this may call for your favourite beverage and a bit of concentration.

What Happens When You Connect a Van?
When you connect a van to your tow vehicle, it obviously puts more load on the rear of your car. If the load is substantial enough, you will see the rear of the car lower and the front of the car lift. Two things are happening at the rear to make it lower. It is easy to see that the rear suspension is being compressed, but what is less easy to see is that the car’s chassis is rotating around the rear axle. The best way I can describe it is that putting the caravan weight on the tow bar is like putting weight on a seesaw — pushing the back down lifts the front up.
We can see that the car is tilted up at the front, but so what? This is a symptom that you may experience potentially experience driving safety problems. I say symptom because the real issue is that, with the caravan attached, the car has more load on the rear axle and less load on the front axle than normal.
If the shift in load off the front axle to the rear axle is great enough, you can experience less precise steering and diminished braking performance. It will also set up altered dynamics within the complete tow rig, with the car and van more likely to pitch up and down. Another side effect can be your headlights pointing up, shining into oncoming traffic rather than at the road.
We spoke to Deon Van Deventer, head of Okajaro Caravan Engineering Specialists. He has decades of experience in RV and automotive engineering and was happy to shed some more light on the impacts on cornering and braking. He explained, “Hypothetically, if you put enough weight on the rear of the car you would lift the front wheels off the ground, in which case you would have absolutely no steering or front brakes. Obviously in practice it doesn’t get to this extreme, but it helps to emphasise the point that the more you lighten the front of the car, the less safe it becomes.
“So, we have the van on the back of the car which is unloading the front axle somewhat. This means there is less down force on the front tyres, which may cause the tyres to have less contact on the road, and less contact means less traction. Less traction and less down force makes it harder for the front tyres to hang onto the road and corner precisely when you turn the steering wheel. Decreased tyre contact patch on the road is also detrimental to braking performance. As the majority of the braking performance in a vehicle travelling in a forward direction is delivered through the front brakes, unloading the front axle has a compounding detrimental effect.”

Why Use a Weight Distribution Hitch?
Described most simply, the weight distribution hitch shifts some of the load imparted by the caravan off the rear axle onto the front axle. With a correctly rated distribution hitch, properly fitted, you will be able to see the car can sitting in a level position. The important thing, however, is that the returned load to front axle means you have restored the front tyre contact patch. Restoring the balance between the front and rear loads can also stabilise the bouncing effect that can be apparent when a heavy caravan is attached to a tow vehicle. A bonus benefit is solving upward pointing headlights.
In principle, weight distribution hitches use levers to put upward force on the tow bar. This causes the chassis to rotate around the rear axle lifting the rear of the car (reducing the load on the rear axle) and lowering the front of the car (increasing the load on the rear axle) to counteract the caravan pushing down on the towball.
The levers used in weight distribution hitches are known as spring bars, which attach to the tow hitch at one end and, once lifted, attach to the A-frame at the other end with brackets and chains. What is actually happening is a bit of load you have lifted off the rear of the car is now hanging off the A frame.
Deon Van Deventer describes it as follows: “The spring bars are like the handles of a wheelbarrow. When you lift the bars (and attach them to the A frame), they transfer the weight forward, ‘pushing’ the front of the car down and lifting the rear of the car.
“Links of chain are part of the connection between the spring bar and the A frame. Using more chain links lengthens the chain, creating less rear lift and less tension in the system, while using less chain links creates more rear lift and creates more tension in the system. Getting the chain length right is a critical part of the system set up process.”

Why Not Just Beef up the Car's Rear Suspension?
Using stiffer springs or using variable pressure air bags in the rear of the car might appear to give the same result, as you can make the car level again, but it is only addressing the symptom.
Stiffer rear suspension results in less spring compression and less lowering of the rear of the car. But it won’t change the fact that the van is still pushing down on the towball, transferring more load onto the rear axle and less load onto the front axle.

Can I Put More Weight on the Ball?
Even though the car will sit more level, fitting a weight distribution hitch doesn’t magically make the ball weight go away — it just shifts the location of the load weight. You can’t use fitting a weigh distribution hitch as a reason to exceed your towball limit.

Is There a Downside?
Weight distribution hitches do put stresses through the tow vehicle’s towbar and chassis and the caravan A-frame. Many vehicles can handle it, but the forces are increased significantly when the van articulates to its extremes up and down. Therefore, weight distribution hitch manufacturers advise that the system needs to be disconnected when travelling over uneven ground, such as spoon drains. This can be inconvenient but may cause vehicle damage if you fail to do so.

Selecting Your Product
We headed to market leaders Hayman Reese for insights into choosing the right weight distribution hitch. Phil Cleven, Hayman Reese Product Manager explained, “The ball weight will determine the correct system for your setup. There are a number of models to accommodate different ball weights. In basic terms, the spring bar ratings vary to achieve enough rigidity to hold the system up and enough flex to accommodate road movement. To give you an idea there are 5 models to accommodate the following towball weight ranges: 0–80kg, 80–135kg, 135–275kg, 275–365kg and 365–545kg. The best way to determine the ball weight is to use a ball weight scale, and the van needs to be loaded as you would use it to provide a meaningful number.
“The weight distribution system also needs enough clearance to ensure the spring bars don’t come into contact with the A-frame. We note how the coupling is positioned on the A-frame (i.e., at the top, middle or bottom) and the depth of the A-frame to help select the most suitable style.”
As you can see, weight distribution systems are quite involved. We recommend you check with your local Hayman Reese distributor to determine the best solution to suit your needs.

Out in the Real World
We have given you a rundown on the theory of weight distribution hitches, including the pros and cons and selecting the right model — but there are other variables that come into play. Some car manufacturers specify that a weight distribution hitch is required when towing — even if your rig is perfectly balanced. On the flip side, some car manufacturers specify that a weight distribution hitch can’t be used. This creates the challenge that if you don’t comply with what the car maker says you may void your car warranty or insurance claims may be rejected.
Our go-to expert for all things aftermarket, Andrew Phillips from The RV Repair Centre shared, “We find the best way to help our customers is for them to bring their car and van to us fully loaded, including passengers, as if they are going on holiday (obviously if the van has been identified as unsafe to tow in this state, we would make another plan). We then do the ball weight measurements with our scales and assess the ride angle of the car to select the most suitable weight distribution system. We are conscious of identifying the suitability of the hitch setup. Some tow systems are not designed to deal with the upward force imparted by the weight distribution hitch.
“We also give practical advice on using the system. For example, attaching the weight distribution system involves raising the hitch point with the van connected. We find it helpful to use the jockey wheel to raise the hitch point before attaching the weight distribution hitch. This takes a lot less effort than levering up the spring bar. We identify the most suitable chain length to level the vehicle and then we mark the ‘right link’ so the customer doesn’t have to guess when they are hitching up. We also advise customers when you want to remove the system, it is important to park the rig on level ground with the van aligned straight to the car. This prevents there being any exaggerated loads in the system making it easier and safer to remove.”

Should I Fit a Weight Distribution Hitch?
Unsurprisingly, the answer is it depends. A weight distribution hitch is not always required. There are plenty of rigs getting around very safely without them. If your tow vehicle sits quite level when hitched up, your van is relatively light, the rig feels balanced, and you don’t experience loss in braking or steering performance there may be no great benefit to having one fitted.
However, if you are experiencing an upward pointing car, a bouncy ride or diminished steering and braking performance, weight distribution hitches can definitely make your tow rig safer.

When in Doubt, Consult a Professional
Improper use could lead to injury, death, or property damage. Selection and fitment should only be undertaken by persons with suitable mechanical competence. Information provided is general in nature, not comprehensive and can only be taken as a guide. Individual discretion must be exercised, and persons actions are completely at their own risk. Publishers and creators of this content accept no responsibility for loss or damage.

Thanks to the following for their expert contribution to this article:

Deon Van Deventer, Okajaro Caravan and Trailer Engineering Specialists — okajaro.com.au
Phil Cleven, Hayman Reese — haymanreese.com.au
Andrew Phillips, The RV Repair Centre — thervrepaircentre.com.au