Mass and Dimension Limits for Rigid Vehicles
Key Takeaways
- GVM (Gross Vehicle Mass) is the maximum laden mass of a single vehicle; GCM (Gross Combination Mass) is the maximum laden mass of a vehicle plus any trailer it tows — both are set by the manufacturer and shown on the vehicle's compliance plate.
- General-access dimension limits for rigid vehicles are 4.3 m height, 2.5 m width, and 12.5 m length; rear overhang is limited to the lesser of 3.7 m or 60 % of the wheelbase.
- General mass limits include a 6 t single steer axle and a 10 t single drive axle; axle-group limits (tandem, tri-axle) are higher but the vehicle's plated GVM and GCM still apply as the upper cap.
- Operating above the dimension or mass limits turns the vehicle into an overdimensional or overmass load, which requires a permit and may restrict routes and travel times.
- Per-axle and per-axle-group mass limits are set under the Heavy Vehicle National Law (HVNL) schedules; Victoria applies these limits on its declared network with concessional mass (e.g., higher steer mass with road-friendly suspension) only where the network permits.
GVM vs GCM: the two mass figures on the compliance plate
Every heavy vehicle carries a manufacturer's compliance plate that states two upper mass limits. Knowing the difference is essential because Victorian road law, the Heavy Vehicle National Law (HVNL), and the HR knowledge test all rely on them.
- Gross Vehicle Mass (GVM) — the maximum permitted total laden mass of a single vehicle, including the vehicle's own mass (tare), fuel, driver, passengers, and load. GVM is the ceiling for a rigid vehicle standing alone.
- Gross Combination Mass (GCM) — the maximum permitted total laden mass of the vehicle plus any trailer(s) it is designed to tow. GCM matters once a trailer is attached.
A rigid truck plated at 22 t GVM and 30 t GCM can be loaded up to 22 t on its own axles. If it tows a dog trailer, the sum of the truck's laden mass and the trailer's laden mass must not exceed 30 t. Exceeding either figure is an offence under the HVNL — the operator, driver, and (under Chain of Responsibility) other parties can all be liable.
Dimension limits: general access for rigid vehicles
A rigid vehicle operating at or below the general-access limits may travel on most of the Victorian declared road network without a permit. Exceeding any of the following turns the vehicle into an overdimensional (OD) load requiring a permit.
| Dimension | General-access limit (rigid vehicle) | Notes |
|---|---|---|
| Height | 4.3 m | Measured from ground level to the highest point of the vehicle or load. Bridges, overpasses, and overhead wires are the most common height hazards. |
| Width | 2.5 m | Measured across the vehicle or load, excluding retractable mirrors and lights. |
| Length | 12.5 m | A rigid truck (not a bus). A bus has a 14.5 m general-access limit. |
| Front overhang | 1.9 m forward of the front axle centreline (load forward of headlights limited to 1.2 m) | Projecting loads must be marked. |
| Rear overhang | The lesser of 3.7 m or 60 % of the wheelbase | Wheelbase = distance from front axle centreline to rear axle-group centreline. |
| Side projection of load | 150 mm beyond the side of the vehicle | Loads wider than the vehicle may need a permit and flags. |
The rear overhang rule trips up many candidates. "Wheelbase" for a vehicle with a rear axle group means the distance from the front steer axle centreline to the centreline of the rear axle group (the midpoint of a tandem or tri-axle group), not to the rear-most axle. The 60 %-of-wheelbase and 3.7 m figures are alternatives: you comply if your rear overhang is within both limits, i.e., within the smaller of the two.
Example: a rigid truck with a 5.0 m wheelbase. 60 % of 5.0 m = 3.0 m. The lesser of 3.7 m and 3.0 m is 3.0 m. The rear overhang limit is therefore 3.0 m for that truck. A truck with a 7.0 m wheelbase gives 60 % = 4.2 m, but the absolute 3.7 m cap applies, so the limit is 3.7 m.
Axle mass limits: steer 6 t, single drive 10 t
Under the general mass limits (GML) in the HVNL mass schedules, individual axles and axle groups each have a maximum permitted mass. For a typical two-axle rigid truck (single steer, single drive), the figures you must know for the Victorian test are:
- Single steer axle: 6 t (general access). A higher steer mass (6.5 t or 6.7 t) is available on vehicles fitted with road-friendly suspension, but only where the route allows — many local roads and bridges cap steer mass at 6 t.
- Single drive axle: 10 t (general access for a single drive axle on a rigid vehicle). Tandem drive axle groups can carry more (commonly 16.5 t under GML with road-friendly suspension, or 15 t on standard suspension).
- Tandem axle group (two axles close together, e.g., a rear tandem on a rigid truck): commonly 16.5 t under GML with road-friendly suspension.
- Tri-axle group: commonly 20 t or 21 t depending on suspension and road-friendliness.
The key principle: the vehicle's plated GVM is the absolute ceiling. Even if individual axle limits would theoretically allow more, the truck may not exceed the GVM on its compliance plate. The same applies to GCM for a combination.
Why dimensions and mass are tested together
The Victorian HR test pairs mass and dimension questions because the two interact. A load that is within the GVM may still breach a dimension limit (a tall pallet inside a curtain-sider that pushes height past 4.3 m, or a long steel beam that breaches rear overhang). Conversely, a load that fits within dimensions may still breach mass limits (a short, dense load that exceeds the steer or drive axle mass). You must check both before driving.
Conversions and road-friendly suspension
Higher axle-group mass limits generally require road-friendly suspension (air or compliant spring suspension that meets the HVNL technical standard) and may also depend on tyre width. "Concessional mass" above GML requires either a network-access approval or a permit, and may be limited to specific routes or vehicles. In Victoria the NHVR issues mass permits; VicRoads manages route approvals.
Pre-trip mass check
Before driving a laden rigid vehicle you should confirm:
- The sum of axle masses does not exceed each axle/axle-group limit.
- The total laden mass does not exceed the vehicle's plated GVM (or GCM if towing).
- The load sits within 4.3 m height, 2.5 m width, 12.5 m length, and the rear-overhang rule.
- If any limit is exceeded, an overdimensional/overmass permit is in force and the route is approved.
A weighbridge is the definitive check. Police and Transport Safety Services (TSS) officers can direct you to a weighbridge; refusal is an offence under the HVNL (covered in Chapter 2).
A rigid truck has a compliance plate showing GVM 22 t and GCM 30 t. The truck's own laden mass is 19 t and it is towing a loaded dog trailer with a laden mass of 13 t. Which statement is correct?
A rigid truck has a wheelbase of 6.0 m (front axle centreline to rear axle-group centreline). What is the maximum permitted rear overhang?
Which of the following general-access dimension limits applies to a rigid truck (not a bus) on the Victorian declared network without a permit?
Under general mass limits (GML), what is the mass limit for a single steer axle on a rigid vehicle on general-access roads?