What is a Tag Trailer? Your Complete Australian Guide
A tag trailer is a single, tandem, or tri-axle trailer that connects to the rear of a rigid or body truck using a fixed drawbar and hitch, rather than a turntable that lets the front of the trailer steer on its own. That fixed connection changes how weight moves through the combination: part of the trailer's load transfers onto the towing truck's rear axle, which means the truck itself doesn't need a full bin load or ballast weight just to keep its drive axles legal.
That's the practical reason operators run a tag trailer behind a rigid truck instead of adding a second body or upsizing the truck: it adds carrying capacity to a combination that's already doing a job, without needing a second prime mover, a semi-trailer coupling, or a full second load to balance the axle weights.
This guide covers how a tag trailer differs from a dog trailer and a semi-trailer, the mass limits that apply at each axle count, the tow mass ratio rule that's specific to tag trailers, and how to work out which configuration suits your operation.
A tag trailer connects to a rigid or body truck via a fixed drawbar and hitch, transferring part of its load onto the truck's rear axle rather than carrying its full weight independently like a dog trailer does. For a rigid truck towing a tag trailer, the NHVR sets the tow mass ratio at 1:1.3, meaning the tag trailer can carry up to 1.3 times the towing vehicle's own mass, provided the towing vehicle itself has at least 20% of the sum of the mass limits across all of its own axle groups and single axles.
What Is a Tag Trailer?
The defining feature of a tag trailer is the coupling. It's a fixed drawbar and hitch connection at the rear of a rigid or body truck, not a turntable. That's the key difference from a dog trailer, which also connects via drawbar but has its own front axle group mounted on a turntable that steers independently as the drawbar swings. A tag trailer's front end simply follows the fixed hitch point, with no independent steering axle at the front.
Because the coupling is fixed rather than steered, a tag trailer transfers part of its load through the drawbar onto the towing truck's rear axle. That's a deliberate part of the design, not a side effect: it lets the truck run with less in its own body or bin and still stay legal on drive axle weight, because the tag trailer is carrying some of that mass for it. A truck running solo would otherwise need a full load, or ballast, to keep its rear axle within its rated limit.
This is different again from a semi-trailer, which couples to a prime mover's fifth wheel via a kingpin and carries roughly half its load through that coupling onto the prime mover itself. A tag trailer runs behind a rigid or body truck, not a prime mover, and the coupling mechanics are entirely different: drawbar and hitch, not kingpin and fifth wheel.
Australian Mass Limits for Tag Trailers
General access dimension limits are the same as for any trailer: 4.3m height, 2.5m width. Mass limits depend on the axle configuration.
Single axle group, dual tyres: 9.0 t GML
Tandem axle group, dual tyres: 17.0 t GML
Tri-axle group (not a pig trailer): 21.0 t GML
Source: NHVR, General Mass Limits (GML): Information sheet, published 11 August 2026, reflecting the Heavy Vehicle National Law and Regulation changes that commenced 1 August 2026.
Tag trailers carry one rule that doesn't apply to dog trailers: the tow mass ratio. The NHVR caps a dog or pig trailer at a 1:1 tow mass ratio, meaning the trailer's mass can't exceed the towing vehicle's own mass. A tag trailer gets a higher ratio, 1:1.3, in recognition of the fact that it transfers load back onto the towing truck rather than carrying everything independently. That higher ratio comes with a condition: the towing truck must have at least 20% of the sum of the mass limits applying to all of its own axle groups and single axles. In practice, that means the truck itself needs enough rated axle capacity to carry its share of the combination, not just enough engine and chassis to tow the trailer.
Tag Trailer Configurations
Single axle
Single axle is the lightest and most common entry point for a tag trailer, rated at 9.0t GML. It suits operators who want to add carrying capacity to a rigid or body truck without stepping up to a heavier combination, and it's the simplest configuration to tow, register, and maintain.
Tandem axle
Tandem axle steps the mass limit up to 17.0t GML, the same tandem group rating that applies across semi-trailers and dog trailers. It suits operators moving heavier freight where a single axle group's 9.0t ceiling isn't enough, without needing the extra length and swept path of a tri-axle group.
Tri-axle
Tri-axle is the heaviest common tag trailer configuration, rated at 21.0t GML under general access. It suits the highest payload requirements a tag trailer configuration can offer, at the cost of a longer combination and a wider turning circle than single or tandem axle groups.
What Do People Use Tag Trailers For?
Extending the carrying capacity of a rigid tipper or body truck already doing a haulage job, without adding a second prime mover or semi combination
Earthmoving and civil works, carting spoil, aggregate, and construction material alongside a truck's own bin
Agricultural haulage, including hay, grain, and general farm freight
General freight where a truck operator needs more capacity on a route without upgrading to a B-double or semi combination
Plant and machinery cartage, where a tag trailer is fitted with a beavertail-style rear ramp so equipment can be driven on rather than craned
Midland's Tag Trailers
Midland Pty Ltd manufactures tag trailers at its Parkes NSW and Kyneton VIC facilities, in single, tandem, and tri-axle configurations, alongside flat tops, drop decks, low loaders, dog trailers, and B-doubles. Midland's Tow and Go range covers tag trailers built on an offshore frame with all finishing and fit-out completed in Midland's Australian factory, a practical option when you need a proven configuration without a custom build lead time. Where the freight, ramp fitment, or axle configuration needs to be specced around your exact operation, Midland's custom-engineered builds start from your brief rather than a standard catalogue spec.
Move More With Certainty means the trailer is built around what you're actually carrying, and towing, not adapted after the fact.
How to Choose the Right Tag Trailer
What's your payload target? This decides the axle count. If 9.0t on a single axle group covers your freight, that's the simplest and lightest option. Heavier or more consistent loads push you to tandem or tri-axle.
Does your truck have the axle capacity to tow it? The 1:1.3 tow mass ratio comes with a floor requirement: your towing vehicle needs at least 20% of the sum of its own axle group and single axle mass limits. Check this against your actual truck's rating before you spec a tag trailer, not after.
What are you carrying? General freight and bulk materials suit a flat deck. Plant and machinery need a ramp, typically a beavertail configuration, so equipment can be driven on under its own power.
What's the rest of the combination? A tag trailer is only ever run behind a rigid or body truck, not a prime mover. Confirm your truck's own body or bin configuration and how the tag trailer's load transfer through the drawbar affects your truck's legal drive axle weight.
Frequently Asked Questions
What's the difference between a tag trailer and a dog trailer?
A tag trailer connects to a rigid or body truck via a fixed drawbar and hitch, with no independent steering axle at the front. Part of its load transfers onto the towing truck's rear axle through that coupling. A dog trailer has its own front axle group mounted on a turntable that steers as the drawbar swings, and it carries its full weight independently on its own front and rear axle groups, with the towing vehicle only feeling the drawbar pull. The two suit different jobs: a tag trailer complements a truck's own body load, a dog trailer carries its own weight and tracks tightly through corners.
What's the difference between a tag trailer and a semi-trailer?
A semi-trailer couples to a prime mover's fifth wheel via a kingpin, and the prime mover carries roughly half the semi's load through that coupling. A tag trailer couples to the rear of a rigid or body truck via a fixed drawbar and hitch, a completely different mechanism, and it runs behind a rigid or body truck rather than a prime mover.
How much can a tag trailer carry?
It depends on axle configuration. Under general access GML: a single axle group is rated at 9.0t, a tandem axle group at 17.0t, and a tri-axle group at 21.0t. These figures reflect the NHVR's General Mass Limits information sheet published 11 August 2026, current since the 1 August 2026 Heavy Vehicle National Law changes.
What is the tow mass ratio rule for tag trailers?
For a rigid truck towing a tag trailer, the NHVR sets the tow mass ratio at 1:1.3, meaning the tag trailer's mass can exceed the towing truck's own mass by that ratio. This comes with a condition: the towing truck must have at least 20% of the sum of the mass limits applying to all of its own axle groups and single axles. This is a higher ratio than applies to a dog or pig trailer, which is capped at 1:1 (the trailer's mass must not exceed the towing vehicle's mass), reflecting the fact that a tag trailer transfers part of its load back onto the towing truck rather than carrying it all independently.
Do I need a permit to run a tag trailer?
Not if you're operating within general access height (4.3m), width (2.5m), and the mass limit for your axle configuration. Permits come into play if your load or combination exceeds those limits, or if your route includes roads with specific access restrictions. Check with the relevant state road authority or NHVR if you're unsure whether your combination and route qualify for general access.
Can a tag trailer carry plant or machinery?
Yes, when it's fitted with a rear ramp, commonly a beavertail-style hydraulic or fixed ramp, so equipment can be driven or tracked on under its own power. Not every tag trailer is built this way. A flat deck tag trailer without a ramp suits general freight and bulk materials rather than mobile plant.
What size truck do I need to tow a tag trailer?
It depends on the tag trailer's mass and axle configuration, and on your truck's own rated axle capacity. The tow mass ratio rule requires the towing truck to have at least 20% of the sum of the mass limits applying to all of its own axle groups and single axles, and the tag trailer's mass can be up to 1.3 times the truck's own mass within that rule. A heavier tag trailer configuration, tandem or tri-axle, needs a correspondingly capable truck to tow it legally.
Talk to Midland
Midland Pty Ltd manufactures tag trailers at Parkes NSW and Kyneton VIC, in single, tandem, and tri-axle configurations. If you're not sure which axle configuration suits your truck and freight, tell us what you're carrying and towing, and we'll work through the spec with you.
Related guides:
Dog trailers | Semi trailer types explained | Drop deck trailers