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A vehicle’s gross vehicle mass (GVM) is essentially the maximum weight a vehicle can carry, including its own weight. In passenger cars, the GVM is rarely an issue. In 4×4s and overland rigs though, the GVM plays a much bigger role. Here’s why...
GVM issues explained
HERE’S a startling fact: a vast number of overland 4×4 rigs on our roads are actually illegal. Why? Simply because they exceed the vehicle’s rated gross vehicle mass (GVM).
As already mentioned, the GVM is the maximum permissible weight a vehicle can carry, including the weight of the vehicle itself. If you check your licence disc, there are two important numbers to take note of: GVM/BVM and Tare/Tarra.
We’ve established what GVM is. Tare is the empty weight of the vehicle, so without any passengers and load, and liquids like water or fuel.
Let’s look at a typical scenario as an example: you’ve just bought a Toyota Land Cruiser 4.5 V8 D4-D station wagon. Most of us would agree that, as far as tough overland 4×4s go, this is about as good as it gets.
The Cruiser’s GVM is 3 060kg. Considering that a VW Polo hatch’s GVM is around 1 500kg, the Toyota’s rating sounds just about ideal for some rough-and-tough overland load. But it’s not quite as simple as that. The Land Cruiser’s tare weight is 2 320kg. So, it means you can add a total of 740kg and you will still be legal.
But wait, there’s a catch. Remember the tare weight is the empty weight of the vehicle? So no fuel and load and so on? Let’s add some fuel. The Cruiser’s two fuel tanks swallow a total of 130 litres. One litre of fuel equates to 1kg of weight. So the available load shrinks to 610kg.
Let’s add four passengers, each weighing a slender 70kg. That adds 280kg. The total – and the available weight in the kitty – shrinks to 330kg.
Since you’re planning to tackle some tough trails, you’ve upgraded the Cruiser’s standard all-terrain tyres to more sturdy mud terrains. Which adds about 10kg per tyre (because of the more robust construction of a mud terrain item). That’s 50kg extra.
Now we’re left with 280kg. Front Runner’s lightweight roof-top tent weighs just 43kg, but you will also have to mount it on one of the company’s roof racks... which weighs in at a relatively light 40kg. Add another 83kg to the equation – and the available mass shrinks to 197kg.
Now you still have to fit in your fridge and all the supplies, recovery gear, bedding, cutlery, baggage, binoculars... and you have just under 200kg to play with.
The Toyota Land Cruiser is actually one of the better performers in this GVM scenario. The Jeep Wrangler Rubicon Unlimited fares worse. It’s GVM is 2 540kg, and the tare 2 040kg, leaving just 500kg in the bank.
Add 85kg worth of fuel and four passengers weighing 70kg each,
and you are left with just 135kg.
See the separate box for some more popular overland GVM versus tare examples.
Oh no! What to do now?
So you own a Jeep Wrangler Rubicon 3.6 Unlimited, and you want to take more than just your binoculars on that two-month overland adventure with your three best front-row rugby player pals. Is there anything to be done to do it legally?
And what about warranties? Surely a car company can use the ‘overloading’ excuse if a mechanical component fails under warranty? Yes they can. And they have.
Apparently insurance companies have also realised that the overweight card is a worthwhile one to play when those claims for broken this and broken that land on their tables. And, to add even more fuel to the fire, traffic authorities seem to have jumped on the bandwagon, realising that there is money to be made from weighing 4×4s on national routes.
Alas, changing a vehicle’s GVM rating, even if you beef it up with a heavy-duty suspension and upgrade the braking system, is a huge and expensive undertaking.
All vehicles are registered via the electronic national administration traffic information system (eNaTIS) and your vehicle will need to be reregistered on this system, with the higher GVM rating. However, a private individual can’t complete this process in his own capacity. So you need to contract a vehicle manufacturer, builder or importer that is registered on the eNaTIS system, and is also affiliated with the national regulator for compulsory specifications (NRCS).
The vehicle will then need to undergo a braking test, to make sure the brakes are sufficient for the increased weight rating. This will cost you about R70 000. Next, you will need to supply an accurate centre of mass figure. This number is not normally quoted in your vehicle’s specification sheets. You’ll need to contact the vehicle manufacturer directly. Finding the right person to speak to may be a challenge in itself, especially if it’s a big corporate like Toyota, Ford or VW.
If you can’t get hold of the correct figure, you’ll need someone to weigh the vehicle. This is a specialised weighing process that will add another R20 000. So now you’re already looking at spending around R100 000.
Essentially, if you go through the entire process, the vehicle can be reregistered on the eNaTIS system with the higher GVM rating. Whether it’s worth all the trouble and money, that’s another question.
Above: Overland expeditions require a capable and reliable 4×4. And also one that can legally handle all the extra weight of such an expedition (Photo: Voetspore).
Above: A stock Jeep Wrangler JK Unlimited can carry just 500kg more than its tare weight. Insert: Licence disc for a Mitsubishi. Note the tare of 2 095kg, and the GVM of 2 665kg – so it can carry 570kg. Right: The lighter you can travel, the better,...