Primary keyword: tyre rules for towing

What do GVM, GCM, ATM and GTM actually mean?

Towing weights trip up more Australian drivers than any other part of the rules, so it helps to define each term before we connect it to your tyres. These are the figures set by your vehicle and trailer manufacturers, and the legal limits you must not exceed.

Term	What it means
GVM (Gross Vehicle Mass)	The most your loaded tow vehicle is allowed to weigh, including passengers, fuel, accessories and the tow-ball download.
GCM (Gross Combination Mass)	The most your loaded car and loaded trailer are allowed to weigh together. This is often less than GVM and ATM simply added up.
ATM (Aggregate Trailer Mass)	The most your loaded trailer or caravan may weigh, measured unhitched.
GTM (Gross Trailer Mass)	The weight on the trailer’s own wheels when hitched. ATM = GTM + tow-ball mass.
Tow-ball mass	The download the coupling presses onto your tow bar, usually around 8–15% of the loaded trailer’s weight as a guide.

How do tyres fit into towing weights?

Here is the part most towing guides skip: your tyres are the component that actually carries all of that mass to the road. Every tyre has a load index — a number on the sidewall that corresponds to a maximum kilogram rating at a specified pressure. Australian in-service rules require the tyres fitted to your vehicle to have a load rating not less than the lowest load rating listed on your tyre placard.

When you hitch up a van, the tow-ball download lands on the rear axle of the car. A 200kg ball weight does not just sit on the tow bar — it transfers to the rear tyres, on top of your passengers and luggage. That is why a tow vehicle can be inside its GVM on paper yet still overload a single axle or an individual tyre if the load is poorly distributed.

If you are unsure how to read that sidewall number, our guide on how to read a tyre sidewall and the full tyre load index chart for Australian vehicles translate the figures into kilograms.

Do you need higher load-rated tyres to tow?

Not always — but you must never drop below the placard. Many dual-cab utes and large SUVs already leave the factory with tyres rated well above their kerb weight, precisely so they can carry payload and ball weight. Problems arise when owners fit cheaper, lower-indexed tyres, or plus-size to a fashionable wheel that forces a lower load index.

For heavy towing, some owners step up to XL (extra load) tyres or, on utes and 4WDs, LT (light-truck) construction tyres with stiffer sidewalls and higher load ceilings. The key rule: whatever you fit, its load index must meet or exceed the placard, and ideally give you headroom for the worst-loaded corner. Before changing size, read plus-sizing a dual-cab ute so you don’t trade away load capacity for looks.

What happens if your towing tyres are underrated or underinflated?

Overloading a tyre behaves exactly like running it underinflated: the sidewall flexes more than it was designed to, which generates heat. Heat is what destroys tyres — it degrades the rubber and can lead to tread separation or a blowout at highway speed, usually on a hot day with a full load, which is the worst possible moment. We cover the legal and safety side in detail in what happens if your tyres don’t meet the placard load rating and what happens if you fit the wrong load rating tyres.

Heavier loads also need higher starting pressures. Your placard often lists a separate, higher “loaded” or “towing” pressure — use it. For the full method, including how to adjust for ball weight, see our dedicated guide to tyre pressures for towing a caravan.

Is it a legal requirement or just good advice?

Both. The load-rating requirement is part of the national in-service standards reflected in the Australian Design Rules and state roadworthy rules — a tyre below the placard load index can earn a defect notice and fail an inspection. Exceeding GVM or GCM is a separate offence that can void insurance after a crash, regardless of tyres. The tyre and weight rules work together: legal weights assume legal, correctly rated tyres underneath them.

The technical dimensions and approved fitments behind all of this come from the Tyre and Rim Association standards, and the manufacture-side rules sit in our ADR requirements for tyres and wheels explainer.

Bottom line

Towing legally starts at the tyre: keep every tyre’s load index at or above your placard, stay inside GVM and GCM, distribute the load so no single axle is overloaded, and set load-adjusted pressures. Do that and the weight numbers on your compliance plate actually mean something.

Frequently asked questions

Does the tow-ball weight count towards my car’s GVM?
Yes. Tow-ball download is part of the tow vehicle’s load, so it counts towards GVM and lands on the rear axle and tyres. Weigh the loaded rig if you’re close to the limit.

Can I fit the same tyres to car and caravan?
Not necessarily. Trailer and caravan tyres are often a different size and construction, and must meet the trailer’s own load requirements. Match each to its placard or plate.

Do I need LT tyres to tow?
Not for light towing if your passenger tyres already exceed the placard. For heavy, frequent or off-road towing, LT construction gives more load headroom and sidewall strength.

Should I increase tyre pressure when towing?
Usually yes. Check your placard for a loaded/towing pressure and set pressures cold. Underinflation under load is a leading cause of towing blowouts.

Where do I confirm my exact limits?
Your GVM and GCM are on the vehicle’s compliance/placard plate; ATM and GTM are on the trailer plate. For legal interpretation, check with your state road authority.

Suggested schema: Article + FAQPage. This is general information, not legal advice — confirm figures with your vehicle and trailer manufacturer and your state road authority. External references: RACQ towing specifications and the Australian Government’s Vehicle Standards Bulletin (VSB 14).