Often overlooked and frequently misunderstood, a GVM upgrade is one modification nearly every tow-tug needs.
They say the first step to fixing a problem is admitting you have one, so here it goes. My name is Dan Everett, and I have a weight problem.
Phew, that feels good!
I never really thought of myself as the kind of bloke who’d struggle with weight. I suppose because it doesn’t really happen overnight, y’know? It kinda sneaks up on you. A set of storage drawers here, a long-range fuel tank there, and before you know it, I’m cranking down on the jockey wheel and the spotlights are chasing down possums in the treetops.
I’ll be honest again, it’s not exactly ideal. But surely you’d have to be doing something pretty silly to go overweight in a modern rig…right?
How much is too much?
“That wouldn’t happen to me,” I hear you say. And you may be right, I never was the most sensible bloke. But let’s have a look anyway and see how easy it is to overindulge in the finer things in life, like the previously mentioned drawers and long-range tank. We’ll pick the humble 200 Series LandCruiser as an example. It’s one of the biggest and burliest tow-tugs on the market without tipping into yank tank territory.
With a kerb weight (no accessories or passengers but a full tank of fuel), a typical GXL Cruiser weighs in at 2740kg. With a maximum Gross Vehicle Mass of 3350kg, that leaves a payload of 610kg. Great, right?
Let’s chuck two passengers up front. Say, dad is 90kg and mum is around 65kg. Two kids in the back? Say 40kg each for teens. That gets us down to 375kg left. A roof rack and an awning get it down to 325kg. Throw some drawers in the back and a little 45L fridge, and you’ll still have 200kg left to play with. Not too bad at all, right? Plenty you can do with 200kg.
But let’s hitch up the super lightweight Cub Campers’ L16. At 1900kg, it’s one of the lightest vans on the market, and with just 170kg of ball weight, you’ll still have 30kg left in your payload! Hmm. Things aren’t looking crash hot at all here, are they? That 30kg will barely cover the food in your fridge, let alone the clothes for your trip or the camp chairs in your drawers.
You could replace the drawers with a bull bar, some flash wheels and tyres, and maybe a rooftop tent, but the results would still end up the same…an illegally overloaded 4WD.
How do I fix it?
While the path to becoming overloaded can be complicated, the process for fixing it is quite simple. Y’see, the manufacturers don’t just pluck legal weights out of the air (mostly). They’re based on the specifications of the vehicle’s components and their ability to carry, move, or stop weight.
Companies like Terrain Tamer spend a whole chunk of change breaking down what the limitations are to set those weights, and then engineer upgrades to fix those weaknesses. In some applications like the previously mentioned 200 Series Cruiser, a simple upgrade of springs front and rear has been tested and approved for a 450kg increase in legal GVM. The Part Number is SK022AGVM for the 200 owners reading along at home.
Other rigs may have a little more complicated parts list. SK0071GVM from Terrain Tamer, for example, bumps the payload in a 79 Series dual cab Cruiser from 3300kg to a huge 3950kg, up 650kg. That kit has the usual springs and shocks, but also a rear swaybar kit and side indicators to comply with Australia Design Rule 6. Terrain Tamer’s testing working out the extra stability from the sway bar is one of the factors the 79 needed to safely handle the extra weight.
All the individual components themselves may physically fix the weight issues you’re having, but together they’re tested and signed off to work as a complete package. It’s a “with these components, this vehicle can handle this weight” kinda situation. Fitted pre-rego, the kits can be signed off as Second Stage Manufacturing to be legal in all states, or fitted post-rego and signed off through state-level modification laws.
Will I notice a difference?
Both the short and the long versions of this answer both say yes. By their very nature, if your tow-tug needs a GVM upgrade, then fitting one will make a whole host of improvements. There’s the usual schtick you’ll get with upgraded suspension. Spring rates that suit what you’re actually carrying will provide a less jarring ride, shocks valved to suit will smooth out the bumps, and you’ll get a far more stable ride with less body roll through winding roads.
But there’s a whole bunch of unbelievably dangerous side effects to overloading your rear suspension (particularly towing) that a GVM upgrade will fix. Think of your tow-tug a little like a see-saw, push down on one end and the other lifts. Overloaded rear suspension will push down far more than acceptable levels, lifting the front in the process.
The result, ironically, is not enough weight on the front end, meaning a reduction in turning grip through corners leading to your setup understeering and potentially running wide.
Important things to remember
It is worth mentioning that a GVM upgrade isn’t a magic bullet to all your problems, though. If you’re towing, you also need to consider your Gross Combined Mass (GCM), the weight of your tow-tug and your trailer.
Say you hypothetically had a GVM of 3500kg and a GCM of 7000kg. When your tow-tug weighs 3500kg, your trailer can weigh up to 3500kg. Go ahead and fit up a GVM upgrade that bumps that up to 3800kg, and that 7000kg GCM figure doesn’t change. That means if your tow-tug still weighs in at 3500kg, you can tow 3500kg. But if you load your tow-tug up to its now legal limit of 3800kg, you’ll only legally be able to tow 2200kg.
