Does A GVM Upgrade Increase Your Towing Capacity?

Having a GVM upgrade allows you to go touring with all of the equipment that you need. It means you can carry water, extra fuel, extra spare tyres, tools and accessories.

But there are some caveats that you must take into account. Not all GVM upgrades increase your towing capacity.

In the case of the new Land Rover Defender and Discovery 5, you can’t do a GVM upgrade on their fancy monocoque chassis.

In the case of Toyotas, Nissans and American trucks, you can, but there are important differences between each.

Broadly, GVM upgrades exist in three categories:

  • Mild (about 3.9 tonnes).
  • Decent (about 4.2 tonnes). These will typically upgrade your rear axle to about 2.5 tonnes.
  • Extreme (about 4.45 tonnes). This is the max limit allowed on a car license. If you were to go above this, you’d need a Light Rigid license.

Let me give you a few tips and tricks about GVM upgrades.

1. Don’t Do A Budget GVM Upgrade.

You can’t step up to heavier GVMs by simply upgrading your suspension (springs and shocks) only.

You’ll need to consider upgrading your wheel bearings, sway bars, upper and lower control bars, axle, diff housing and possibly brakes and clutch.

Upgrading GVM isn’t as simple as adding some axle braces.

You may also need a diff drop kit, new upper control arms and (maybe) adjustable Panhard rods to correct caster and camber, as well as shaft and CV angles.

Some aftermarket companies will offer you a “mild” GVM upgrade that consists of airbags only.

“Just stick a set of airbags in the rear and she’ll be right”.

This type of advice can work, but in a very limited set of situations.

Some controversy surrounds airbag use, as they do nothing to help you strengthen the chassis or other suspension components. Instead, the airbags simply transmit all of the force to the chassis, which is not designed for the load.

Here’s a quote from an ARB mechanic:

“The point loading that the airbags create (rather than being spread over the length of the chassis occupied by a leaf spring) means that any weight aft of the bags, or towed weight, is likely to cause issues. Throw in the horrendous pounding these vehicles cop on our corrugated roads and you have a recipe for an unscheduled extension in Alice.”

Importantly, he added:

“Airbags are in no way designed to increase the vehicles GVM, we clearly state this on our marketing hand-outs, product packaging and instructions.”

“From an engineering stand point, the airbags create a third point of contact (usually at the bump stop strike plate which is designed to handle severe impact) to ‘assist’ in the load carrying of the vehicle,” he continued.

“In cases where we know the vehicle will constantly be on its upper limit of capacity, we recommend that the leaf pack and even shock absorbers be upgraded from factory spec for a more even load share along the chassis rail.” 

2. Ensure That Your GCM Is Raised.

The other critical fact you need to consider is GCM. Not all GVM upgrades raise your GCM, which means they don’t increase your towing capacity.

In other words, they’re almost worthless in the context of towing.

AEV, for example, will raise your GVM to 4.2 tonnes while preserving your 3,500kg towing capacity – at GVM.

ARB, meanwhile, explicitly states that their GVM upgrade “doesn’t alter the towing capacity or Gross Combination Mass (GCM) of the vehicle”.

Practically speaking, it means that an LC200 with an ARB 4025kg GVM upgrade cannot tow a caravan that’s heavier than 2825kg when loaded to its GVM. Its CGM of 6850 creates this limit. In case you’re wondering, most 21-foot caravans weigh 2700-3200kg TARE.

Companies that do GVM upgrades on most models are:

  • Pedders – Ford Ranger, Nissan Navara, Toyota Hilux, Mitsubishi Triton, Holden Colorado, VW Amarok, Mazda BT50, GU Patrol, LC 79, LC 200
  • Lovells (4000 GVM / 1900 front / 2100 rear)
  • AEV / JMaxc
  • ARB
  • Dobinsons
  • DMW

3. Upgrade Your Rear Axle.

When towing in a touring vehicle, you’re almost always likely to hit your rear axle limit before you hit your GVM.

It means a GVM upgrade that doesn’t raise your rear axle’s rating by at least a couple of hundred kilograms is worthless.

For example, the LC200’s OEM rear axle is rated at 1950kg and, until recently, some GVM upgrade companies only raised that by 50kg, to 2000kg, as part of their 3850kg GVM upgrade. This type of upgrade is a waste of your money.

For reference, the ARB 4015 GVM upgrade increases the front axle rating from 1700kg to 1870kg and the rear from 1950kg to 2145kg.

4. Consider A Chassis Extension.

An extension, or a “chop”, as it’s commonly called, can extend the length of your chassis by between 300mm and 750mm, with 650mm being the most popular.

What are the main reasons for doing it?

More payload and better weight distribution across axles.

What people often don’t realise is that most cars carry the vast majority of their payload over the rear axle. If you take a look at your vehicle, you’ll notice that apart from the bullbar, winch and a 2nd battery, any weight you add will typically be over – or, worse, behind – the read axle. This makes it easy to exceed the rear axle’s load capacity and to create an unbalanced vehicle. Too much weight over the rear takes pressure off your front tyres, creating light, vague, wandering steering.

A chassis extension mitigates these issues by moving the pivot point of the rear axle further back.

Stay safe by loading your vehicle proportionately.

Moreover, in the context of towing, a chassis extension also helps create a more sure-footed vehicle by increasing its wheelbase. (The longer the wheelbase, the less your vehicle be pushed around by a large van).

Are there any downsides to chassis extensions? You bet. Here are 3 reasons why I don’t love the idea of chassis extensions and why I’d consider it only as a last resort:

  • Considerable cost. Cutting a new 4WD in half is not a cheap exercise. Budget at least $25K.
  • Less agility. A chassis extension increases the 4WD’s turning circle, which makes carparks and tight offroad tracks more tricky to navigate. More importantly, it reduces your ramp-over angle. The longer the extension, the worse it becomes. This makes your vehicle a lot more likely to get hung up on rutty, hilly tracks.
  • More weight. By the time you’re done, you’ll have a vehicle that weighs about 3300 kg tare and will have about 1 tonne of payload. It will also have 5 seats and a canopy. That’s a lot of empty space just begging to be filled. And believe me – you will fill it. Your 4WD will weigh at least 4 tonnes in touring mode.

These 3 factors combine to create an expensive, bloated 4WD. Don’t get me wrong – it will still be an offroad weapon by most standards, but using it for spontaneous exploration will require a lot more deliberation, more caution and more planning.

If you get it bogged to the sills in mud on a tight track (and this is more likely when you weight 4+ tonnes all up), recovery can be a very tricky affair.

This is why I prefer wagons to canopies, especially when towing a caravan. The car remains agile and light exploration machine. The caravan serves as a home base full of creature comforts.

The uncomfortable truth is that most of those “monster” chopped LandCruisers with huge canopies serve as on-road caravan haulers. They leave the tarmac mainly to do some mild beach driving.

If you do decide to look into chassis extensions, check out DMW, ASG and AEV – they’re the three standout players in the market.

5. Be Prepared To Fiddle.

A GVM upgrade is not something you “set and forget”.

Expect to do quite a bit of fiddling to get your car’s ride and handling optimal.

You may need to adjust your coil’s preload rates or upgrade/downgrade your coils.

6. Check Your Wheel And Tyre Ratings.

Your wheel and tyres, like everything, have legal limits.

If you push your GVM up you may find that you’ll need to upgrade your existing wheels and tyres, as well.

As a rough guide, you’ll definitely need to do this if you’re upgrading your GVM to 4200 kg and above; you may get away with your existing gear if you’re staying under that threshold. Here’s what you need to do:

  • weigh your SUV’s individual axles at GVM
  • divide each number by two to understand how much weight each wheel will be carrying
  • check your wheel and tyre ratings and ensure that they exceed the figures in your previous calculation

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