Fo­cus on tech

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...

Leisure Wheels (South Africa) - - CONTENTS -

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,...

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