GVM is one of the least thought-about variables in the equation of setting your 4X4 up for touring. When you think about it, this is kinda scary… as not paying attention to your GVM can have some pretty serious ramifications. If you like the idea of risking a bent chassis, cooked brakes, voided insurance and automatically being at fault in an accident, then skip on over this article; but if you like being on the right side of both the law and physics, then you need to make a cuppa and have a bit of a read.
For those who aren’t aware, GVM stands for gross vehicle mass – and it refers to the total amount of weight your 4X4 can handle safely. And pretty much everything affects it. From throwing an extra couple of passengers in to filling your fuel tank to topping up the fridge with a few beers to bolting some barwork to your bus to fitting a winch to running bigger tyres to packing the camping gear – it all goes on the GVM.
Now you may think that driving a 4WD gives you a fair bit of wriggle room here – most of them have ladder chassis and heavy-duty suspension (at least compared to a passenger car), and in the good old days this may well have been the case. But there’s been a disturbing trend over the past couple of decades. 4X4s are getting wider, longer and heavier; but perversely, the amount of weight they can carry has been shrinking. What the…???
To see if we can get to the bottom of all this and find out what can be done to keep your vehicle legal, we thought we’d put together this article to show just what you can carry, what you can bolt to your four-wheel drive, and what options you have when the weights you need to have on board are greater than what’s legally allowed.
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KERB WEIGHT – This is essentially the vehicle’s weight when unladen. It often includes a token amount of weight for a partially-filled fuel tank and a driver, but it’s essentially the stock weight of a 4X4.
GVM – Gross Vehicle Mass, or the most a 4X4 can weigh. It can vary through models and trim levels, but is always included on the VIN plate.
GCM – Gross Combined Mass, the maximum amount of weight both vehicle and trailer can add up to. It should ideally be the GVM and braked tow rating added together, but often it isn’t (just to make things even more confusing).
ATM – Aggregate Trailer Mass. The weight of a trailer. As a side note, the Gross Trailer Mass (GTM) is the ATM minus the amount of ball weight on the vehicle’s tow bar.
BALL WEIGHT – The force (in kilograms) exerted downwards on a vehicle’s tow ball by a trailer.
PAYLOAD – The difference between the GVM and the kerb weight of a vehicle. Effectively how much weight it can carry. It includes things like fuel, passengers, bar work, tents, awnings, winches, fridges… you name it.
AXLE LOAD – How much weight the front and rear axles can handle safely. The sum of both axle ratings usually adds up to more than the GVM, giving a bit of flexibility as to where the weight is distributed on the vehicle.
BRAKED TOW RATING – How heavy a trailer (with trailer brakes fitted) the vehicle can tow. As we’ll see in this article, tow ratings are to be treated with a healthy degree of scepticism; but we’ll get into that in a bit…
PAYLOAD – WHAT IS IT AND HOW IS IT DETERMINED?
Payload and GVM are closely related. If you work out how much weight your vehicle has on board when unladen – so let’s say 10L of fuel, a front bar and maybe a set of drawers and fridge in the back – the difference between that weight and the GVM is the payload. It’s basically a measurement of how much weight you can carry.
Let’s take a 200 Series LandCruiser as an example. They have a GVM from the factory of 3,350kg and a curb weight of 2,705kg (VX turbo-diesel model), leaving a payload of 645kg. Seems fairly substantial, right? But bolt on a bullbar and winch (60kg), a rear bar and a second spare (70kg), a set of drawers (60kg), a 60L fridge on a slide (60kg), a rack (30kg), roof top tent (70kg), a couple of passengers (150kg), a water tank (80kg) and a full long-range fuel tank (120kg) and that weight can be reached, and exceeded, very easily (we’re now at 700kg by the way – or 55kg over GVM, and thus illegal). And that’s without a dual battery system, ball weight from a trailer, camping accessories or tools and recovery gear. Scary, ain’t it!
GVM UPGRADES WHAT’S INVOLVED?
Don’t throw away your 12V microwave and put your eight-tonne caravan on the market just yet though. There are things you can do to upgrade your GVM so your vehicle can handle the extra weight safely. The first and most important step is to work out what weights you’re going to be carrying. Chances are you’ll be able to get sorted with little more than a suspension upgrade with springs that are rated to suit the loads your vehicle will be hauling. If you’re looking at towing a 25-foot caravan around the country, you may have to up the ante a little and talk to your 4WD specialist about having some reinforcement plates and possibly an extra cross-member welded to your chassis. This is a serious modification though, and it will need to be signed off by an accredited engineer. It may well be more worthwhile upgrading to a bigger vehicle to handle the load safely, but this varies on a case-by-case basis – your local 4WD store will get you pointed in the right direction.
WHY ARE PAYLOADS GETTING SMALLER?
You’d think with 4X4s getting progressively wider, longer and heavier their ability to carry weight would be increasing too; but unfortunately this isn’t always the case. Take the Toyota HiLux as an example. Compared to 20 years ago the current models are bigger and comfier in just about every way. However the payload is shrinking. A 2016 SR5 dual-cab has a GVM of 3,000kg and a payload of 925kg. Compare that to the 2008 model and you’ll find a 2,795kg GVM and a 990kg payload.
So why can the older model carry 65kg more on a 200+kg lighter ute?
There’s a range of factors that could account for this. Comfier seats and padding on the interior, heavier frames, larger panels, more electronics and larger gearboxes all add up and collectively take their toll on the GVM. Keep in mind also that as you add accessories to your vehicle, they’ll decrease the overall payload figures. Keeping things light is almost always better here.
HEAVIER VEHICLES AND SHRINKING GVMS
It’s a similar story with wagons, too. While the newer vehicles have impressively large GVMs, their kerb weights are higher than ever as well – effectively reducing the amount of weight they can carry. This is somewhat offset by higher-tech engines that deliver better power and economy, but at the end of the day you can’t escape the physics. There are some exceptions to the rule, but the trend of shrinking GVMs is becoming clear and is more than a little worrying. When shopping for a new vehicle, think about the accessories you’ll likely be fitting, the gear you take into the bush, and the ball weight of any trailer you’ll be towing – they’ll all affect your available payload capacity and the GVM. Speaking of towing…
3,500KG TOW RATINGS – NOT AS IMPRESSIVE AS THEY SOUND
A few short years ago there weren’t too many options on the market if you wanted to tow a serious load behind you. Today however, almost every dual-cab ute (with the exception of the Triton and Amarok) is rated to tow an impressive 3,500kg (braked). Sounds pretty good, doesn’t it?
The thing is, this number is an ‘official’ rating and fails to take into consideration gross combined mass (GCM – the maximum weight of trailer and vehicle combined) and a trailer’s aggregate trailer mass (ATM) and its effect on your vehicle’s GVM. When it comes to towing, it’s also worth looking at the front and rear axle load ratings, or the amount of weight each axle can handle (which, when combined, usually adds up to more than the vehicle’s GVM). Confusing? Yes, it is.
Let’s take a look at a Nissan NP300 Navara ST-X, which comes with a GVM of 2,910kg and a GCM of 5,910kg. Assuming you’re towing the maximum 3,500kg trailer, subtracting the trailer weight drops the allowable GCM to 2,410kg (or the maximum the vehicle can now weigh).
Now we factor in the kerb weight of 1,980kg: That gives 430kg left over for occupants, bar work, canopies, clothes, awnings and the dog.
“Sounds do-able,” I hear you say. But let’s not forget the ball weight of your trailer, which would ring in around the 350kg mark (supposedly, but it’s not really the case; which I’ll explain in a sec). Yep, that’s taken off your GVM too, leaving you a scant 139kg to play with… so bring your spouse, but leave the dog at home and don’t forget to unbolt the bullbar before you leave.
But wait, it gets worse.
What if you want to tow when you’re already at GVM? The GCM of 5,910kg has to be reduced by the GVM of 2,910kg, leaving us with a 3,000kg towing ability. Sounds OK, doesn’t it? Nuh-uh… we need to factor in those axle loads, too. The Navara’s combined axle loads add up to 3,020kg (1,320kg front; 1,700kg rear), which is only 110kg higher than the GVM. Seeing our vehicle is already at GVM, that leaves us only 110kg of allowable ball weight (or a trailer weighing approximately 1,100kg) – but even that’s aiming high. Because the tow ball is located a metre or so behind the rear axle, the leverage changes the load on the axle (effectively making it greater) – so the reality is that even your 1,100kg trailer would be pushing the friendship between you and your vehicle.
Without boring you with loads of maths, the table above roughly highlights the effect of this leverage.
NAVARA ST-X BALL WEIGHT VS GVM
|ATM||TOWBALL DOWNLOAD||GVM REDUCTION|
So with 350kg of ball weight on our at-GVM Navara with 3,500kg braked towing capacity, you’re well and truly over GCM and putting all sorts of stress on your axles, engine, brakes… everything really. And oh yeah… you’re breaking the law, too.
Moral of the story? While these vehicles can tow that amount on paper, in the real world you’re more than likely going to end up driving an illegal, dangerous rig – all the while putting a huge strain on your mechanical components. If you need to tow big loads regularly, look for something with a higher GCM and GVM, and the highest torque numbers you can find. Vehicles like 200 Series LandCruisers and Land Rover Discovery 4s are much more suited to heavy towing tasks than a dual-cab… unless you’re talking something like an F250 or Dodge Ram. But you get the point.
BEING OVER GVM – IT’S EASIER THAN YOU THINK
In case you haven’t picked up what we’re putting down here, it’s incredibly easy to exceed your GVM when you’re loaded up for an extended trip through the Outback. Take a new Ford Everest Titanium 4X4 with the 3.2L turbo-diesel as a case study. They come with a 3,100kg GVM, 605kg payload (with 80kg being able to be carried on the roof) and a 3,000kg braked towing capacity (as a side note – top-spec models are almost always a little heavier and consequently have a slightly lower payload). Those are decent numbers by any estimation, and a fair representation of SUVs across the mid-size market.
Let’s say you’re towing your Cub Campers Brumby camper trailer along for your trip, which comes with a 160kg ball weight. You tick the box at the dealer for the factory bullbar and tow pack and throw a set of quality driving lights on – call it 50kg all up.
You’ve got a family, so you invest in a roof rack (20kg) to store the bulky gear up out of the way; and throw a set of drawers (60kg) in the back to keep everything accessible. You like to hit the remote destinations, so you throw a long-range tank underneath (120kg when full). Sounds pretty reasonable, right? Nothing too over the top?
With you, your partner and two teenage kids on board (275kgs or so), you’re now at 685kg worth of payload. That’s 80kg over the limit of what the vehicle is designed to carry. And that’s not factoring in any number of things like clothes, camping gear, the dog, the Esky, the mother-in-law or your trick 12V satellite TV set-up so you can watch the grand final while out in the bush…
OK, let’s be honest here – nobody is getting busted for being over GVM. But still, it’s definitely something to think about… especially in the event of things going pear-shaped and you end up in a bingle and your insurance company decides it’s not going to cover you. Priced the cost of a new front bar from Ford (or any other manufacturer) lately? They ain’t cheap!
At the end of the day you don’t have much to play with here guys; and keeping an eye on the weights being carted should be part of your packing regime. There are options for upgrading the GVM with some aftermarket suspension, ranging from 400-600kg increases in load-carrying capacity, which will cover a lot of bases; however it’s absolutely imperative that you don’t go over your GVM. The consequences are just too heavy (see what I did there?).
TOP SELLING NEW 4X4S AND THEIR GVMS
|Holden Colorado 7||2820kg||610kg|
|Jeep Grand Cherokee||2949kg||701kg|
|Jeep Wrangler (wagon)||2540kg||571kg|
|Land Rover Discovery IV||3240kg||675kg|
|Mercedes G Wagen||3200kg||588kg|
|Mitsubishi Pajero Sport||2710kg||640kg|
|Nissan Y61 (wagon)||3060kg||582kg|
|Range Rover Sport||3200kg||802kg|
|Range Rover Vogue||3250kg||762kg|
|Suzuki Grand Vitara||2100kg||480kg|
|Toyota FJ Cruiser||2510kg||510kg|
|Toyota LandCruiser 200 Series||3350kg||610kg|
|Toyota 70 Series (dual-cab ute)||3300kg||1095kg|
NB: All models top-spec and dual-cab where applicable.