What Is a GVM Upgrade? JMACX Options for WA 4WD Owners

A GVM upgrade increases the maximum legal operating weight of a vehicle.

It can provide additional load capacity for passengers, accessories, tools, touring equipment and the weight transferred onto the vehicle when towing.

This becomes important because a standard 4WD can reach its original weight limit faster than many owners expect.

Bull bars, winches, long-range fuel tanks, roof racks, drawer systems, dual-battery systems and larger wheels all add weight. Once passengers, luggage and tow-ball weight are included, the available payload can reduce considerably.

A properly approved GVM upgrade can increase the amount of weight the vehicle is legally permitted to carry. However, the upgrade must be selected, installed and certified correctly.

What does GVM mean?

GVM stands for Gross Vehicle Mass.

It is the maximum permitted weight of the vehicle when loaded and ready to drive. This includes more than the vehicle itself.

Weight contributing to GVM can include:

• The vehicle
• Fuel
• Driver and passengers
• Bull bar and winch
• Roof rack
• Drawer system
• Canopy or service body
• Additional batteries
• Long-range fuel tank
• Tools and recovery equipment
• Camping equipment
• Luggage
• Tow-bar and towing accessories
• Tow-ball download from a trailer or caravan

If the vehicle weighs more than its approved GVM while being driven, it is overloaded.

What is payload?

Payload is the usable amount of weight available for people, accessories and cargo.

A simple starting calculation is:

GVM minus the vehicle’s starting weight equals available payload.

However, the vehicle’s advertised payload may not reflect its real-world capacity after accessories have been fitted.

For example, fitting a bull bar, winch, roof rack, larger tyres, dual-battery system and rear storage can use a substantial part of the original payload before passengers or luggage are added.

The most reliable way to understand your current position is to weigh the vehicle in the condition in which it is normally used.

For a touring vehicle, that means weighing it with:

• Fuel
• Regular passengers
• Touring accessories
• Recovery equipment
• Water
• Tools
• Typical luggage
• Trailer or caravan connected where relevant

This produces a more useful figure than relying only on catalogue specifications.

Why do 4WD owners consider a GVM upgrade?

Many 4WD owners do not start with the intention of building a heavy vehicle.

The weight usually accumulates as accessories are added over time.

A typical touring build may include front protection, a winch, suspension, larger wheels and tyres, roof storage, drawers, a fridge, additional fuel, a second battery and towing equipment.

Every component may have a clear purpose, but every component also adds weight.

A GVM upgrade may be suitable for vehicles used for:

• Caravan towing
• Remote touring
• Mine-site and commercial work
• Carrying tools or equipment
• Heavy tray and canopy builds
• Family touring
• Long-distance travel
• Vehicles with extensive accessories

The objective is not simply to fit heavier suspension. It is to create a tested and approved setup that increases the legal operating mass of the vehicle.

What is included in a JMACX GVM upgrade?

JMACX produces engineered GVM upgrade packages for selected Toyota, Ford, Ram and INEOS platforms.

Depending on the vehicle and approved package, a JMACX GVM upgrade may include components such as:

• Upgraded springs or coils
• JMACX Alpha shock absorbers
• Control arms
• Sway-bar components
• Extended sway-bar links
• Struts
• Differential or driveline components
• Vehicle-specific suspension hardware
• Engineering and compliance documentation

The exact components vary between vehicles and GVM ratings.

A LandCruiser 300 Series package will not use the same parts or approval as a LandCruiser 70 Series, Prado 250 or Toyota Tundra package. The approved bill of materials for the selected kit must be followed.

JMACX currently lists GVM applications for platforms including the LandCruiser 70, 200 and 300 Series, Prado 250, Toyota Tundra, Next-Gen Ranger, selected Ram models and the INEOS Grenadier range. JMACX

Pre-registration GVM upgrades

A pre-registration GVM upgrade is completed before a new vehicle receives its first registration.

This work must be completed under the relevant federal Second Stage Manufacturer approval. The vehicle is then first registered at its upgraded GVM rather than its original manufacturer rating.

Pre-registration is often worth considering when a new vehicle is already being planned for:

• A complete touring build
• Heavy towing
• A tray and canopy
• Commercial equipment
• Additional fuel capacity
• Extensive accessories
• A known operating weight

Planning the GVM upgrade before the complete build begins allows suspension, accessories, tyres and intended load to be considered together.

Post-registration GVM upgrades

A post-registration upgrade is completed after the vehicle has already been registered and used on the road.

In Western Australia, an in-service vehicle upgrade must follow the relevant state approval process and receive the required modification permit.

This option may suit owners who already have their vehicle or who discover that their completed build has insufficient payload.

A post-registration upgrade is not simply a suspension replacement. It requires an approved kit, correct installation and the appropriate compliance process.

Does a GVM upgrade increase towing capacity?

Not automatically.

GVM, GCM and towing capacity are separate ratings.

GVM is the maximum permitted weight of the loaded tow vehicle.

GCM is the maximum permitted combined weight of the tow vehicle and connected trailer.

Braked towing capacity is the maximum trailer weight specified by the vehicle manufacturer, subject to the vehicle remaining within all other applicable limits.

Increasing the vehicle’s GVM does not automatically increase its GCM.

If the GVM is increased while the GCM remains unchanged, loading the vehicle to its higher GVM can reduce the remaining weight available for the trailer.

For example, a vehicle may legally carry more weight after a GVM upgrade but still be restricted by its original GCM, axle ratings or towing capacity.

This is why a towing setup needs to be assessed as a complete combination rather than looking at one number in isolation.

Does a GVM upgrade increase payload?

An approved GVM upgrade can increase the vehicle’s legal load-carrying capacity.

However, the usable increase will depend on:

• The new approved GVM
• The vehicle’s actual weight
• Front and rear axle limits
• Accessory weight
• Passenger load
• Tow-ball download
• The approved components
• Any GCM limitations

An increased GVM does not mean every kilogram can be placed anywhere on the vehicle.

The front axle, rear axle and individual tyre load ratings must still remain within their approved limits.

Good weight distribution remains important.

Will the vehicle ride differently?

A GVM upgrade may change the way a vehicle rides.

Suspension designed to support a greater operating mass can feel firmer when the vehicle is empty or lightly loaded. The final result will depend on the selected spring rate, shock absorbers, tyre pressure and usual operating weight.

JMACX Alpha suspension options can include manual or in-cab electric shock adjustment on selected applications. This allows the suspension behaviour to be adjusted to suit changing vehicle loads and driving conditions.

However, suspension selection should begin with the vehicle’s expected weight. Adjustable shocks cannot correct a spring or GVM package that was poorly matched to the vehicle’s intended use.

Can approved GVM components be changed later?

Care needs to be taken when changing any component that forms part of an approved GVM upgrade.

The kit is certified using a specific combination of components. Replacing those parts with unapproved alternatives may invalidate the upgrade and return the vehicle to its original specifications.

This can include changes to:

• Springs
• Shock absorbers
• Control arms
• Sway bars
• Wheels and tyres
• Other certified suspension components

Speak with an Authorised JMACX Facility before changing anything included in the approved package.

Should the vehicle be weighed first?

In most cases, yes.

Weighing the vehicle helps determine whether it is already close to its GVM or axle limits.

It also gives the workshop better information when planning the correct package.

For the most useful result, record:

• Total vehicle weight
• Front axle weight
• Rear axle weight
• Tow-ball weight where applicable
• Normal passenger load
• Planned accessories
• Expected cargo

If the vehicle is still being built, provide a complete list of the accessories that will be fitted. Estimated component weights can then be considered during the planning process.

Choosing the right JMACX GVM upgrade

The highest available GVM is not automatically the correct choice for every vehicle.

The package should suit:

• The vehicle model and year
• Pre or post-registration status
• Normal operating weight
• Front and rear axle loads
• Towing requirements
• Tyre size
• Suspension height
• Accessory plan
• On-road and off-road use
• Preferred ride characteristics

A daily-driven LC300 with occasional towing may require a different setup from a heavily loaded touring build.

Likewise, a work vehicle carrying tools every day should be assessed differently from a vehicle that is usually empty and only loaded for occasional trips.

The GVM upgrade process at Hunter Mechanical

Hunter Mechanical plans the GVM upgrade around the complete vehicle rather than treating it as an isolated suspension job.

The process generally includes:

1. Reviewing the vehicle and intended use
2. Confirming pre or post-registration status
3. Discussing current and planned accessories
4. Reviewing payload, towing and tyre requirements
5. Selecting the appropriate approved JMACX package
6. Installing the required components
7. Completing wheel alignment and workshop checks
8. Arranging the applicable compliance process
9. Providing the vehicle owner with the relevant documentation

Planning the whole build early can also help coordinate the GVM upgrade with wheels, tyres, protection equipment, towing accessories and other modifications.

Frequently asked questions

Are GVM upgrades legal in Western Australia?

Yes, provided the upgrade uses the correct approval pathway, is installed correctly and receives the required certification or modification permit.

Is pre-registration better than post-registration?

Neither option is automatically better for every owner. Pre-registration can simplify planning for a new vehicle, while post-registration allows an existing vehicle to be upgraded. The compliance process is different for each.

Does a GVM upgrade increase my towing capacity?

No. A GVM upgrade does not automatically increase GCM or the manufacturer’s towing capacity. The complete towing combination must remain within every applicable rating.

Can I fit heavier springs without completing a GVM upgrade?

Heavier springs may help the vehicle support its normal load, but they do not increase the legal GVM by themselves. A legal GVM increase requires an approved and certified upgrade.

Will a GVM upgrade affect my warranty or insurance?

Any vehicle modification may affect warranty or insurance coverage. Owners should discuss planned modifications with the vehicle manufacturer and insurer before proceeding.

Can I change the suspension after the upgrade?

Only approved components should be used. Changing components included in the certified package may invalidate the GVM approval.

Which vehicles can Hunter Mechanical upgrade?

Available JMACX packages include selected LandCruiser 70, 200 and 300 Series vehicles, Prado 250, Toyota Tundra, Ranger, Ram and INEOS platforms. Availability and ratings depend on the model, year and registration status.

Discuss your GVM requirements with Hunter Mechanical

Hunter Mechanical is an Authorised JMACX Facility in Western Australia.

Our team can assess your vehicle, payload, towing requirements and planned accessories before recommending the appropriate pre-registration or post-registration package.

GVM upgrades and complete 4WD builds are available through our Kenwick, Rockingham and Karratha workshops.

Learn more about GVM upgrades in Perth

Explore the JMACX range

Contact the Hunter Mechanical team for a GVM upgrade quote.