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Understanding caravan weights

The acronyms and calculations behind caravan weight can be a very confusing topic, even among seasoned caravanners, but taking the time to understand it is essential. 

One of the most discussed aspects of caravanning is weight. Yet it’s also the most misunderstood because of the numerous definitions and the innumerable combination of vans and tow vehicles. The number of overweight vehicles on the road is a worry, and the evidence is all around us. Authorities run regular vehicle checks and the number of non-compliant vans over the scales totalling around 70 per cent. 

Two things are at play. Either caravanners don’t understand the regulations, or they know the law yet choose to avoid the issue in the hope they aren't caught or, more naively, don’t have an accident. We talk about caravan weight a lot because it’s essential. Lives are potentially at risk.

So, when considering a van, weight should be a top priority. And in the caravanning equation, there are three parts – the tow vehicle, the van and the combination of the two. You must be across all three to be safe and legal once you hit a public road. Getting a good grasp on weight can be overwhelming, and there are many acronyms to confuse us. Let’s break it down.

Tare (van)The unladen weight of the van with all permanently fitted accessories
Tare (vehicle)The unladen weight of the tow vehicle with 10L of fuel
Kerb weight (vehicle)Generally the unladen weight of the car with full fuel tanks
ATM (van)Aggregate Trailer Mass. The maximum legal weight of the van when loaded, including ball weight
GTMGross Trailer Mass. Maximum weight on the caravan tyres when hitched to a tow vehicle. Doesn't include tow ball mass
GVM (vehicle)Gross Vehicle Mass. Maximum legal weight of the vehicle with everything loaded, including passengers, fuel and tow ball weight
GCMMaximum legal combined mass of tow vehicle and van
TBMTow ball mass or weight. The weight of the van on the ball. Each tow vehicle will have a maximum TBM specified in the owner's manual
PayloadThe difference between Tare weight and ATM. It’s the maximum that can be legally carried

You will find the main specifications for the van on the compliance plate, although this changes to an online log for new vans built under the new RVSA standards.

While most of these definitions will be self-explanatory, the issue of ATM seems the least understood. The Aggregate Trailer Max is the maximum weight set by the manufacturer when the van is loaded. It isn't the weight of the van. For example, you could legally tow a 3500kg plated van with a Prado, which has a maximum towing capacity of 3000kg if the total van weight is less than 3000kg. 

Tare weight can also be confusing. The tare should include all accessories fitted at the build stage. However, any accessories supplied later will eat into the payload available. 

Ball weight has a secondary consideration, and that's the ratio of caravan weight to ball weight, and it needs to be in the 5-10% range for optimum weight balance. Some examples might be helpful. If the van, when loaded, weighs 2500kg and the ball weight is 320kg, then the ball has 12.8% of the load. This will place undue pressure on the ball and cause sway in some situations. Similarly, if the van weighs 3000kg, but the ball weight is 100kg, then the ratio is only 3.3%, meaning there is too much weight at the back. Sway is almost inevitable.

You may think the sway control system will save you in this situation. It might. But it might not. Eliminating the weight balance problem is better than hoping technology has everything in hand.

The tow vehicle

To say that to successfully tow anything the vehicle needs to be powerful and heavy enough to safely travel at highway speeds might sound obvious. Still, I have seen some highly unsuitable combinations in my travels. In the golden age of caravanning, the family car could happily tow the van to the annual holiday, but things have changed. Vans are much heavier, and the current family car will likely be a four-cylinder version. 

Generally, it's wise for the tow vehicle to be heavier than the trailer. A van weighing around 85% of the tug will aid stability and handling.

Most folk now choose a 4WD as their preferred tug simply because they generally have the power and towing ability. However, there is an extensive range of offroaders, and some are more suited than others. For example, the very popular Prado is limited to a van, weighing in at 3000kg when loaded. Even so, that still leaves plenty of suitable on and offroad models it can safely tow. 

Most twin cab utes are rated to 3500kg, and many are very capable. Then there are the seven-seat options like LandCruiser, Patrol, Jeep and some of the Europeans that are also rated to a maximum towing weight of 3500kg. 

But there’s a catch or two. The first is the vehicle’s maximum weight rating or gross vehicle mass (GVM). Looking at what’s probably the most popular tug for big vans, the 200 Series LandCruiser, we see the Kerb weight is 2740kg, and its maximum legal weight (GVM) is 3350kg. With a stock standard vehicle that leaves a theoretical payload of 610kg. Great eh? Well, not really. If you add some of the usual accessories like a bull bar, winch, tow bar, cargo barrier, radio, lights and drawers – around 290kg you have 320kg of payload left. Add in two occupants at, say, 80kg each, fuel and some tools and recovery gear, and there's 40kg of legal capacity left, and you still have to hitch the van with its tow ball weight. Suddenly you are over legal GVM.

Getting the correct specifications of accessories from some suppliers is very difficult, and the weight of those oversized heavy items they are trying to sell you might be a touchy subject. So, the only accurate measure of your modified vehicle’s weight is to put it over a weighbridge. 

I recently went through this process with my own 100 Series, and I was surprised at how heavy it was despite my mental arithmetic adding up the best guess of all the add-ons. I bought it with lots of gear, but after the weighbridge shock, I removed some unnecessary accessories and pared back nearly 150kg to make it legal. Looking around now, I reckon many well-kitted vehicles we see are illegal. The proviso might be that they have undergone a GVM upgrade, but that's a story for another day.

The second consideration is GCM or gross combined mass: the total legal weight of the tow vehicle and van. Again, using the 200 as an example, its rating for GCM is 6850kg. We have seen above that it's easy to max out the legal vehicle weight of 3350kg. However, if you are within that limit, you have 3500kg for towing, so the 200 is legal at those rates. To be sure, it would be wise to check the weights at each axle to ensure they meet specified limits because if the vehicle is overweight, it could also exceed the GCM figure.

From its specifications, the new Ford Ranger is an excellent example of a tow vehicle with room for accessories and still enough in its maximum ratings to be legal. Kerb weight is 2129kg, and the payload is a whopping 1151kg, so there's scope for adding the MSA catalogue of add-ons. Even so, if you max out the GVM of 3280kg, you have a combined mass that limits the van to 3120kg. 

While 200’s GVM rating lives up to its good towing cred, and the Ranger has some scope for towing, it’s not the case for many of the other twin cab utes, though. For example, the D-Max has a decent 986kg payload but a GVM of 6000kg, leaving 3000kg for a van if the tow vehicle is at maximum load. 

The Caravan Industry Association has a valuable weight calculator on their website, where you can add your planned accessories to your vehicle to calculate the total weight. Go to www.caravantowing guide.com.au and open the Know Your Weight file to see what adding accessories will do to your GVM.

Pack right

As well as limiting the load in your van and vehicle, where you load it is also vital, and the trick is to balance the load and keep heavy items low for the best centre of gravity. Check your owner's manual to see how much weight the roof rack can carry because extra weight up top can have a nasty effect on handling. 

Incorrect loading causes most problems with a swaying caravan. It's often an issue of packing too much at the rear of the van and taking weight off the tow ball. Manufacturers put a lot of emphasis on designing their van so it handles correctly, so they know more than the average owner about modifications. If you want two spares and an extensive toolbox at the back, then ask for it at the time of build. Placing extra weight on the rear bar is asking for trouble because it will bite you one day in the wrong conditions at speed.

Overloading the front toolbox might not be as dramatic as putting too much weight at the rear, but you risk maxing out your ball weight if you go too far. This puts undue pressure on your car's rear axles and suspension and can even affect steering. Imagine the pressure an even legally loaded van puts on the drawbar and vehicle components over rough roads at speed. It's not sensible to test the laws of physics.

Packing carefully inside is also essential; the trick is only to take what you really need. Keep heavy items low and as much to the centre of the van as possible. Refrain from overloading high cupboards with lots of tinned food or bottles. 

A properly loaded van should sit evenly on the tow bar. Conversely, a caravan with a prominent drop at the rear indicates that there's too much weight at the back and that the van will sway dramatically.

Ignorance isn’t bliss

We hear anecdotal evidence that insurance companies refused payouts after an accident because the van was too heavy. Following a recent fatal accident in NSW involving an overweight caravan, police collected all the contents of the van for weighing. The van was proven overweight, and the driver was convicted and gaoled. 

An NRMA insurance spokesperson told us they have received very minimal claims that can be attributed to weight issues. However, if weight was deemed to be a contributing factor in a claim, then this might lead to a denial, depending on the circumstances and surrounding factors

Under NRMA Insurance Caravan policy, it is the customer’s responsibility to ensure that their caravan meets RTA requirements for being legally towed including the weight of a caravan and its contents.

A claim may not be accepted if it is determined that the caravan has been illegally towed or used in an illegal manner.

Caravan owners should check the maximum towing load recommended by the vehicle manufacturer. Keep in mind that additional contents such as water, gas, food and camping gear can add weight to a van.

The acronyms and tech talk around caravan weight can be confusing, but it’s not impossible to understand. If you are worried, the best step is to approach one of the professional weighing companies. They can ensure you are legal and give valuable weight distribution and packing advice.

It’s up to the driver to know the law around the limits of the van and vehicle combination because safety is paramount. We hear many stories where authorities have set up weighing stations to target caravanners. In many instances, warnings have been handed out, but we shouldn't presume this leniency will prevail. Any police officers can issue fines and demand resolution to an overweight problem at any time, so getting stuck in the middle of nowhere is possible if your van is severely overweight.