What is Aggregate Trailer Mass (ATM)?

ATM is the total weight of the trailer plus its maximum cargo load. It is stamped on the trailer's compliance plate and must never be exceeded. ATM = Tare Weight + maximum cargo. All legal requirements — brakes, axle config, safety chains — are assessed against this number. (Reference: VSB 1 §1.5)

What is Gross Trailer Mass (GTM)?

GTM is the portion of the trailer's total weight carried by its own axles. GTM = ATM − Tow Ball Download. Since the tow ball download (≈ 10% of ATM) is transferred to the tow vehicle, GTM is approximately 90% of ATM. QLD trailer brake requirements are based on GTM, not ATM — per VSB 1 §5.3. (Reference: VSB 1 §1.5, §5.3)

What is Gross Vehicle Mass (GVM)?

GVM is the maximum weight your towing vehicle is legally allowed to be — including fuel, passengers, luggage, accessories, and the downward force of the tow ball (ball download). Exceeding GVM is illegal and affects vehicle handling. Check your vehicle handbook or door placard.

What is Gross Combined Mass (GCM)?

GCM is the maximum total mass of your towing vehicle plus the fully loaded trailer. Even if your vehicle's tow rating allows a heavy trailer, GCM may be the binding limit. GCM is listed in your vehicle handbook — subtract your vehicle's laden weight to find how much your trailer can actually weigh.

Tare weight is how much the trailer itself weighs when completely empty. Maximum cargo = ATM − Tare. Tare is usually shown on the trailer's compliance plate or in the manufacturer's documentation. Towing accessories (e.g. a toolbox or spare wheel mounted to the trailer) count as part of the tare.

What is Tow Ball Download?

Tow ball download is the vertical load the trailer hitch transfers to the tow vehicle's tow ball. VSB 1 §4.3 recommends this be approximately 10% of ATM. Too low (under 5%) causes dangerous trailer sway; too high overloads the rear axle of the tow vehicle. Your vehicle has a maximum ball download rating — check the handbook. (Reference: VSB 1 §4.3)

What is Vehicle Standards Bulletin 1 (VSB 1)?

VSB 1 is published by the National Heavy Vehicle Regulator (NHVR) and covers all technical requirements for light trailers (ATM ≤ 4.5 t): structural integrity, coupling height, braking systems, lights, reflectors, safety chains, and more. All trailers used on Australian roads must comply. Manufacturers build to VSB 1; modifications must not violate it. (Reference: NHVR VSB 1 (2021))

What is Australian Design Rules (ADR)?

ADRs are mandatory national standards set by the Australian Government for all road vehicles. For trailers, the most relevant is ADR 38/00 (Braking Systems for Trailers). Trailers sold new in Australia must comply with applicable ADRs as part of the type-approval process.

What is AS 4177.4 — Safety Chains (AS 4177.4)?

AS 4177.4 specifies the minimum strength rating and attachment method for trailer safety chains. At least one chain is required for trailers up to 2,500 kg ATM; two high-tensile chains are required above 2,500 kg ATM. Safety chains must be rated to hold the full ATM of the trailer. (Reference: AS 4177.4 + VSB 1 §6)

What is National Heavy Vehicle Regulator (NHVR)?

NHVR is the national regulator for all vehicles over 4.5 t GVM. For light trailers, NHVR publishes VSB 1 and related guidance. The NHVR website (nhvr.gov.au) is the authoritative source for VSB 1, mass management, and heavy vehicle law.

What is Transport and Main Roads (TMR)?

TMR is the Queensland government department responsible for vehicle registration, driver licensing, road rules, and vehicle standards. All trailer registrations in QLD are processed through TMR. Visit tmr.qld.gov.au for registration forms, fee calculators, and authorised examiner searches.

What is Safety Certificate?

A Safety Certificate (commonly called a "roadworthy") is issued by a TMR-authorised examiner after physically inspecting the trailer. It confirms the trailer meets minimum safety standards for registration. Required for: second-hand trailers, trailers transferred from another state, and modified trailers. Valid for 2 months from issue date.

What is Registered Professional Engineer of Queensland (RPEQ)?

An RPEQ is a professional engineer licensed by the Board of Professional Engineers of Queensland (BPEQ). For homemade or significantly modified trailers, an RPEQ must physically inspect the trailer and issue an Engineer's Certificate confirming it meets VSB 1 before it can be registered. Search for vehicle/trailer-experienced RPEQs at bpeq.qld.gov.au.

What is Compulsory Third Party Insurance (CTP)?

CTP covers personal injury caused by a registered motor vehicle. In Queensland, trailers do not require their own CTP policy — the towing vehicle's CTP covers the trailer while it is being towed. However, trailers are still required to be registered and you may want additional general liability or property damage insurance separately.

A single-axle trailer is supported by one set of wheels. It is standard for lighter trailers (ATM ≤ 750 kg). Above 750 kg GTM, brakes must be fitted. Above 2,000 kg ATM, a single axle becomes structurally inadequate and a tandem axle is strongly recommended or required.

A tandem axle trailer has two axles (four wheels per side), providing better load distribution, stability at highway speeds, and redundancy if one tyre fails. Tandem is strongly recommended above 750 kg ATM and mandatory above 2,000 kg ATM under QLD TMR rules. All tandem trailers above 750 kg GTM require at least one braked axle.

What is Electric Breakaway System?

An electric breakaway system consists of a self-contained battery and a brake controller on the trailer. If the trailer detaches from the towing vehicle, the system automatically applies full braking force to all trailer wheels and holds it for a minimum of 15 minutes. Mandatory under VSB 1 §5.3.3 for all trailers with GTM exceeding 2,000 kg. (Reference: VSB 1 §5.3.3)

What is Service Brake?

A service brake is a friction braking system on the trailer's axle(s), connected to and activated by the towing vehicle's brake pedal (via electric or hydraulic controller). VSB 1 §5.3.1 requires a service brake on at least one axle when GTM exceeds 750 kg. Above 2,000 kg GTM, brakes are required on all wheels. (Reference: VSB 1 §5.3.1)

Free QLD Trailer Tools — Compliance Auditor, Size Guide & 3D Load Planner

QLD Trailer Compliance & Sizing Tools Free Queensland trailer tools based on VSB 1 and QLD TMR guidelines — work out compliance (ATM, GTM, braking, axle configuration), the right trailer size, registration steps, and how your load fits in 3D.

Trailer Compliance Auditor

Trailer Size Recommender