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Published Oct 2024
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By: Brendan Batty
If we are to believe the hype surrounding modern vehicle marketing, towing your dream caravan or trailer is as simple as buying the latest SUV and hooking up. But, there’s more to consider than where you’ll be lighting your first campfire.
Absolutely key to getting there safely is how well the weight of your new caravan and all your gear is distributed across the car.
Get it right, and the trips will be unforgettable. Get it wrong, and they’ll still be unforgettable, but not for the same reasons.
What is weight distribution?
Weight distribution is simply how the total mass of a vehicle (including passengers, luggage, accessories and appendages like trailers) is spread across its contact points with the road – the tyres and axles. The ideal is to spread it all evenly so that no one point is significantly more loaded than another.
From the factory, your car or four-wheel drive will have an ideal balance, which might be that 45 per cent of the vehicle’s mass is over the front wheels and the other 55 per cent is over the rear.
Adding weight anywhere on the vehicle changes its dynamics. To a certain extent, the engineers who dreamt up your car accounted for it – a ute with a few hundred kilos of tools in the tray usually rides better than one with gym bags and kids’ scooters. But there are limits, and there are scenarios that exacerbate poor weight balance more than others. Adding weight behind the rear axle is one of those scenarios, and that’s precisely what we do when we hitch up a trailer, especially heavy ones like caravans, boats and camper trailers.
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By adding weight behind the rear axle, we’re creating a lever where the pivot point is the back wheels. As more weight pushes down on the back, it lifts the front, like a seesaw. But the spread of weight isn’t even. If you weigh the rear axle as you hitch your caravan, you might notice that the weight increase is more than the weight of the hitch itself.
If you apply weight behind the axle, it'll remove weight from the front axle
In one example demonstrated by the NRMA, adding 250kg of ball weight to an Isuzu MU-X increased the rear axle load by 380kg. That’s more than half its allowed rear axle load (roughly 600kg), just because of 250kg of extra weight. That additional 130kg didn’t appear out of nowhere, either. It had been transferred back from the front axle, which then had 130kg less weight over it.
Interestingly, weight distribution isn’t affected by how firm or soft the suspension is. Just fitting ‘stiffer’ suspension to fix rear-end sag won’t solve the problem. The caravanning magazine ROAM measured the effect tow ball load had on axle weights with normal and blocked out suspension. The front end still got lighter even if the rear end didn’t sag at all.
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How do you fix poor weight distribution in a caravan?
There are two sure-fire ways to fix an imbalance in your car and caravan, and in combination, they work a treat. The best way is to ensure your combination is packed so that the car’s rear end isn’t overloaded. That might be as drastic as getting a new car (bigger, with more load capacity) or new caravan (smaller and lighter). Of the two, the latter is probably the smarter choice.
For those on a budget, you might just have to pack less and avoid packing or fitting heavy accessories to the front (or back) of the caravan. We’re looking at you, large toolboxes and motorcycle racks.
If you’ve packed the trailer or caravan and it’s still heavy over the tow ball, using a weight-distribution hitch is the only way to shift weight from your car’s rear axle to the front wheels. These work by levering the car in opposition to the caravan, forcing the front end down. At the same time, this removes weight from the rear axle, so it’s possible to undo any potential overload.
The easiest way to know if you’ve got the right amount of weight over the front axle is to measure the front wheel arch height. If it’s the same with and without the caravan, or slightly lower, you’ve got the car well balanced. There’s more weight on the car, so the rear will sink a little, also. If the front wheel arch is significantly higher than it was before, your balance is not right, and you need to change something.
RELATED:How to safely pack your car, caravan or trailer for a road trip »
The nose-up profile of this 4WD could indicate the rear end's overloaded
Why is weight distribution so important?
When the caravan puts so much weight on the rear that it levers the front end up, its ability to brake effectively is seriously hindered. With less weight on the front wheels, the forward bias of a braking system is compromised.
In the same example demonstrated by the NRMA, it was found that the MU-X and 2.5-tonne caravan could stop three metres sooner when fitted with a weight-distribution hitch – 25m versus 28m.
Three metres might not sound like much, but after 25m of hard braking, the car without the weight distribution hitch was still travelling at 30km/h. That’s fast enough to set off the airbags. Or kill a pedestrian.
Proper weight distribution will also help avoid caravan sway, about which there’s more detail below. With the correct amount of weight over the front of the tow vehicle, the caravan will have a harder time ‘pushing’ the car around, and the car will have better steering feel (it won’t be light and airy).
It will also improve the ride and handling of the car. The suspension at both ends will have more range and won’t feel too wallowy in the front and too firm or bumpy in the back. In the long run, tyre wear will also benefit. All of which makes for a much more enjoyable holiday. And that’s the only reason to go caravanning, right?
Need some more caravan advice before setting off?
We're running free caravan safety training sessions in Perth and regional WA to help you travel safely.
Last updated: June 2024
