How to Increase Towing Capacity Legally in Australia

Increasing a vehicle's legal towing capability is not a single modification. The achievable trailer mass is controlled by several separate ratings, and a change to one rating does not automatically change the others.

In Australia, the available approval pathway depends on the vehicle, whether it is new or already registered, and the state or territory in which it is registered.

Start with the limits that already apply

A towing combination must comply with all relevant limits at the same time, including:

• the tow vehicle's GVM and axle ratings;

• Gross Combination Mass (GCM);

• braked towing capacity (BTC), where specified;

• towbar, coupling and towball-download ratings;

• the trailer's Aggregate Trailer Mass (ATM), Gross Trailer Mass (GTM) and axle ratings;

• tyre and wheel ratings; and

• applicable registration, licence, mass and road-access conditions.

The lowest applicable limit controls the combination.

GVM, GCM and BTC do different jobs

GVM is the maximum permitted loaded mass of the motor vehicle.

GCM is the maximum permitted combined mass of the motor vehicle and the trailer or trailers it is towing.

BTC is the maximum braked trailer mass the vehicle is permitted to tow under the applicable rating.

Increasing GVM does not automatically increase GCM or BTC. Increasing GCM does not automatically increase BTC. A heavier-duty towbar cannot increase the vehicle's BTC by itself.

Check actual masses correctly

Use measured axle-group masses in the intended travelling configuration rather than brochure tare figures.

When coupled, towball download is carried by the tow vehicle and forms part of its axle and GVM loading. The trailer's wheels carry the GTM component. Adding the coupled tow vehicle mass, which already includes towball download, to the trailer's full ATM would count the towball load twice.

A useful weighbridge assessment records the tow vehicle's front and rear axle masses and the trailer axle-group mass, with the combination loaded as it will travel.

Possible ways to improve the towing setup

Depending on the limiting factor, the lawful solution may be to:

• reduce or redistribute vehicle load;

• reduce trailer load;

• change the tow vehicle or trailer configuration;

• obtain a GVM upgrade where available;

• obtain a GCM re-rating where the jurisdiction provides a pathway;

• obtain a BTC re-rating only where a lawful pathway exists;

• upgrade trailer ATM, GTM, axles or brakes where technically and legally available; or

• use a vehicle with suitable original ratings.

The correct solution should be identified before purchasing suspension, towing or trailer components.

Can GCM or BTC be increased after registration?

There is no single Australian answer.

Queensland publishes the LS16 code for certain light-vehicle GCM and BTC re-ratings. Western Australia permits eligible GCM re-ratings under VTB-181A while retaining the original equipment manufacturer's BTC and states that BTC cannot be re-rated under that pathway. Other states and territories use their own engineering, approval and registration processes and may restrict or decline particular rating changes.

For heavy vehicles, VSB 6 Section S provides technical requirements for certain rating modifications, subject to the relevant regulator and jurisdiction.

This is why advice that a component or certificate is “legal Australia-wide” should be treated cautiously.

Pre-registration vehicles

Before first supply, an approved Second Stage of Manufacture process may alter applicable ratings under the Commonwealth Road Vehicle Standards framework. The completed vehicle must be covered by the appropriate approval and entered on the Register of Approved Vehicles.

A pre-registration SSM approval and a post-registration modification approval are different pathways.

What an engineering assessment may include

The assessment depends on the proposed rating and vehicle but may address:

• original vehicle, axle, tyre, wheel and towing ratings;

• chassis and tow-load paths;

• suspension, steering and wheel-bearing capacity;

• braking performance and trailer-brake compatibility;

• handling, stability and electronic safety systems;

• engine, transmission and cooling capability;

• towbar and coupling design;

• representative axle-group masses; and

• testing and evidence required by the applicable approval code.

Fitting stronger springs alone does not demonstrate higher towing capacity.

Practical approval sequence

1. Record the vehicle, trailer and all current ratings.

2. Weigh the combination in representative loaded and coupled conditions.

3. Identify the actual limiting rating.

4. Confirm the registration jurisdiction and available pathway.

5. Complete an engineering feasibility assessment before modification.

6. Install only the approved design and retain component records.

7. Complete the specified inspection and testing.

8. Obtain the required certificate, plate, permit or registration update.

9. Notify the insurer and confirm the modified combination is covered.

Certification documents a particular approval; it does not guarantee insurance cover, warranty or interstate acceptance.

Official references

• Commonwealth: Second Stage of Manufacture

• NHVR: VSB 6

• Queensland: LS16 Gross Combination Mass Re-rating

• Western Australia: GVM and GCM FAQs

• Transport for NSW: caravans and towing

Technical content reviewed 13 August 2026. Confirm the current pathway with the registration authority for the vehicle's jurisdiction.

KME can assess which rating is constraining a proposed combination and whether an engineering pathway is available. See GCM and BTC engineering services.