Frequently asked questions (FAQs) explaining the requirements and process of obtaining a Gross Vehicle Mass (GVM) and Gross Combination Mass (GCM) upgrade in Western Australia (WA).
Note: Throughout our FAQs we refer to Vehicle Technical Bulletins 180A and 181A, which provide detailed guidance on vehicle standards and inspection requirements. Both bulletins are available for download:
Gross Vehicle Mass (GVM)
What is a GVM upgrade?
A GVM upgrade involves upgrading certain vehicle components to allow the vehicle to carry a heavier load than rated by the vehicle manufacturer.
What is the difference between a pre-registration and a post-registration GVM upgrade?
For a brand-new vehicle to be modified prior to first licence, the modifier must have been granted Second Stage Manufacturer (SSM) approval by the Federal Department of Infrastructure, Transport, Regional Development, Communications, Sports and the Arts (DITRDCSA). Any GVM upgrade kit fitted by an SSM must also be approved by the Federal Government.
Any modification done to an in-service vehicle, that is a vehicle that has been licensed and is on the road, must be approved by the Department of Transport and Major Infrastructure (DTMI) and a modification permit issued.
Who can legally perform a GVM upgrade in WA?
Only a Federally approved SSM or one of their approved contractors can fit a GVM upgrade to a brand new, unlicensed vehicle.
Any licensed mechanical workshop that is an approved installer of a certified GVM upgrade kit can perform a GVM upgrade to an in-service vehicle. Alternatively, a workshop may modify the suspension to include a GVM upgrade and have the modifications certified by automotive consultant and approved by DTMI.
In each case, a modification permit must be issued by DTMI.
Will a GVM upgrade cause increased wear & tear on my vehicle?
Any modification that results in the vehicle operating beyond the original rating limits set be the vehicle manufacture has the potential to increase wear and tear on the vehicle.
Is my vehicle warranty affected when fitting a GVM upgrade?
Any modification done to a vehicle has the potential to affect the vehicle warranty coverage. DTMI strongly advises anyone thinking of modifying a vehicle to check with their vehicle manufacturer before undertaking any modification.
Will a GVM upgrade affect my vehicle’s insurance coverage?
Any modification done to a vehicle has the potential to affect the insurance coverage. DTMI strongly advises anyone thinking of modifying a vehicle to check with their insurance company before undertaking any modification.
Can I still tow a trailer or caravan after a GVM upgrade?
Yes, you can. However, it is important to remember that upgrading the GVM of a vehicle without upgrading the GCM will reduce the weight of trailer that can be towed when the vehicle is loaded to its new maximum mass.
Will ride quality change in my vehicle after a GVM upgrade?
Yes, the ride quality may well change. In general, a vehicle fitted with a GVM upgrade kit will have a noticeably harder and stiffer ride than a standard vehicle, especially when lightly laden.
The ride in my car with a GVM upgrade is too hard and uncomfortable. Can I change the springs for different, softer ones?
Yes, you can fit softer springs. However, it is important to understand that fitting different components than those approved as part of the GVM upgrade kit will invalidate the GVM upgrade approval and mean that the original (pre-GVM upgrade) vehicle manufacturers specifications will now apply.
Gross Combination Mass (GCM)
Has there been a recent change to the law regulating GVM and GCM upgrades in WA?
Yes. In May 2024, DTMI published Vehicle Technical Bulletins 180A & 181A which specify the standards and requirements for the re-rating of the Gross Vehicle Mass (VTB-180A) and Gross Combination Mass (VTB-181A) of a light vehicle in WA.
The VTBs are based on the equivalent Queensland Modification Code and have been developed in conjunction with the Australian Automotive Aftermarket Association (AAAA).
Any Federal SSM approval for a GVM upgrade doesn't cover re-rating the GCM of the vehicle. This has been the case since the publication of the Federal Administrator’s Circular 0-4-6 in October 2019.
What is the difference between a GVM and a GCM re-rating?
A GVM upgrade will allow a bigger payload to be carried by the vehicle, resulting in greater downwards forces on the vehicle and its components. The components that are generally upgraded to allow for a bigger payload include: shock absorbers, springs packs, spring coils, control arms, sway bars, and struts.
A GCM upgrade will allow for greater downwards forces and lateral forces, that is, forwards, backwards, and side to side movements. As well as the GVM component upgrades, there are various other components and factors that must considered, and requirements that need to be satisfied, before approval can be granted. The areas of consideration include: the chassis, engine, driveline, braking system, differential, cooling system, and towbar, as well as the effects on the vehicle/combination stability.
Does increasing my GVM automatically increase my GCM?
No. Unless the requirements of both VTB-180A and VTB-181A have been met, the GCM can't be re-rated.
My vehicle had a post-registration GCM modification upgrade approved in another jurisdiction and I am now taking up residence in WA. Does the approval automatically apply in WA?
No. A GCM re-rating can only apply to a WA registered vehicle if it is approved by WA DTMI.
Each jurisdiction has their own regulations and rules relating to modifications and who can legally modify and upgrade the GCM of a vehicle.
Although some companies claim that their upgrade kits allow for a GCM re-rating in other jurisdictions, in WA they must have first met the specific component and performance testing outlined in VTB-181A, provided WA DTMI with the reports and supporting documentation, and be granted an approval.
WA law requires that vehicles garaged in WA be registered in WA.
E.g. a customer in Perth purchases a Victorian registered Landcruiser that has been re-rated post-registration by a company in Melbourne. For the vehicle to be licensed with a rerated GVM & GCM in WA, the modifications must meet the requirements of VTB-180A (GVM) and VTB-181A (GCM).
Any re-ratings that don't meet the requirements of the VTBs won't be recognised in WA and the original vehicle manufacturers specifications will apply. In order for the upgrades to be accepted in WA the vehicle must be assessed here.
What about a pre-registration GVM/GCM upgrade from a different jurisdiction? The sticker/plate they installed on my vehicle has a re-rated GCM. Is this GCM accepted in WA?
No. Just like a post-registration GCM re-rating, a GCM re-rating can only apply to a WA registered vehicle if the re-rating is approved by WA DTMI.
My friend has the exact same vehicle with the exact same GVM upgrade, but their modifications were done pre-registration and mine was done post-registration. Why do they get the GCM upgrade, and I don’t?
Unless the GCM re-rating has been approved by WA DTMI, the GCM re-rating would still not be applicable within WA.
I am travelling through WA in my vehicle that has had a GCM re-rating in another jurisdiction. Is the re-rating still applicable?
Any re-rating modifications that have been certified in the state in which the vehicle is licenced will be recognised in all other jurisdictions whilst travelling in that jurisdiction.
E.g. a re-rated Patrol certified and licensed in Queensland is travelling through WA as part of a big lap. Any uprated GVM, GCM and BTC values stated on the modification plate affixed to the vehicle will be recognised by on-roads enforcement officers.
Does increasing my GCM automatically increase my BTC?
No. In WA, the Road Traffic (Vehicles) Act 2012 prevents the towing capacity of a vehicle from being re-rated by anyone except the vehicle OEM. Therefore, as a result:
- VTB-181A can only be used for re-rating the GCM of a vehicle, retaining the OEM BTC rating where a GVM increase has also been performed
- the BTC of a vehicle can't be re-rated
- the GCM of a vehicle can't be re-rated to include any BTC re-rating.
How do I apply to WA DTMI for a GCM upgrade?
An applicant will need to email vsp@transport.wa.gov.au with all relevant information and results including:
- component testing
- performance testing
- SAE J2807 testing
- modification approvals if relevant (e.g. GVM modification)
- checklists.
DTMI engineers will then work through the information and highlight areas that may need more clarification or areas that have been missed. DTMI engineers will work with you if you have any questions or concerns.
Who can legally perform a GCM upgrade in WA?
Only a licensed mechanical workshop that is an approved installer of a certified GCM upgrade kit which has met the requirements of VTB-181A can perform a GCM upgrade in WA.
Why does there need to be so much testing?
Significant resources are allocated by vehicle manufacturers to determine their vehicle’s GCM, ensuring the vehicle is safe, doesn't prematurely wear, and is fit for purpose. The testing outlined in VTB-181A is designed to ensure all the relevant areas that would have been originally tested are still fit for purpose and can handle the increase in payload and component strain.
Why has WA DTMI not released a list of approved GCM re-ratings?
Under VTB-181A, the onus is on the applicant to supply all relevant information. The applicant can be anyone including the modifier, the manufacturer, an engineer, or the vehicle owner. DTMI don't conduct their own testing and can't publicly release the Intellectual Property of the applicants.
Why can’t WA just accept GCM upgrades from all jurisdictions?
As there is currently no harmonised GCM upgrade process, each jurisdiction has their own rules and policies for allowing a GCM re-rating which will be considered based on the jurisdiction’s vehicle regulations and road access
As WA law requires the CEO of DTMI to be satisfied before approving a vehicle modification, evidence that the modifications have been carried out correctly and the vehicle is safe and fit for purpose is required for review as other jurisdictions may not apply the same standards as those set out in VTB-181A.
Definitions
Australian Design Rules (ADR) terminology used
Definitions are taken directly from the Australian Design Rules, which are the national standards for road vehicle safety, anti-theft and emissions made under the Commonwealth Road Vehicle Standards Act 2018.
The total mass of the laden trailer when carrying the maximum load recommended by the ‘Manufacturer’. This will include any mass imposed onto the drawing vehicle when the ‘Combination Vehicle’ is resting on a horizontal supporting plane.
The value specified for the vehicle by the ‘Manufacturer’ as being the maximum of the sum of the ‘Gross Vehicle Mass’ of the drawing vehicle plus the sum of the ‘Axle Loads’ of any vehicle capable of being drawn as a trailer.
The mass transmitted to the ground by the ‘Axle’ or ‘Axles’ of the trailer when coupled to a drawing vehicle and carrying its maximum load approximately uniformly distributed over the load bearing area, and at which compliance with the appropriate Australian Design Rules has been or can be established.
The maximum laden mass of a motor vehicle as specified by the ‘Manufacturer’.
The lesser of either;
- the rating given to the towing equipment fitted to the motor vehicle or,
- the difference between ‘Gross Combination Mass’ and ‘Gross Vehicle Mass’.
Definitions from DTMI’s Safe Towing Guide
The following definitions are taken from the Safe Towing Guide.
The maximum your vehicle can weigh when fully laden. This is the weight transferred to the ground through the wheels with a trailer attached if towing.
The weight imposed on the tow vehicle’s tow hitch (ball or other type) by the coupling of the trailer onto the tow bar.
The mass of the vehicle in running order unoccupied and unladen with all fluid reservoirs filled to the maximum level including fuel, and with all standard equipment.
Is the same as Kerb Weight but with only 10 litres of fuel in the fuel tank instead of a full tank.
The maximum allowable load on that axle (front or rear), as specified by the manufacturer.
The mass transmitted to the ground by the tyres of the trailer when coupled to a vehicle and carrying the maximum load recommended for the trailer, with the weight uniformly distributed over the load bearing areas.
Value specified for the vehicle by the ‘Manufacturer’ as being the maximum weight of the towing vehicle and any trailer while coupled together in their as-used condition. This may be less than the sum of the ‘GVM’ and towing capacity of the vehicle.
The maximum allowable mass or weight of the trailer specified by the manufacturer. ATM is the sum of GTM plus the tow hitch download.
The allowable load carrying capacity or ‘payload’ is worked out by deducting the trailer Tare Mass from the ATM. The payload must not be exceeded under any circumstances. Safety, insurance and warranty may be affected if the specified payload is exceeded.
Other definitions
Tow ball weight, also known as tow ball mass or tongue weight, refers to the amount of weight a trailer or caravan exerts on the tow ball of the vehicle. It's a crucial factor for stable and safe towing, and ideally, it should be between 8 - 10% of the trailer's loaded weight.
Braked towing capacity is the maximum weight of a trailer, equipped with its own braking system, that the vehicle and its towing equipment is rated to tow. This value is specified by the vehicle manufacturer. BTC is based on Aggregate Trailer Mass (ATM), not Gross Trailer Mass (GTM). It is important to understand that the BTC quoted by the vehicle manufacturer may not be the same as the RTC and it may not be possible to tow a trailer at BTC if the tow vehicle is at its maximum weight (i.e. at its GVM) without exceeding the GCM.