Buying or loading a trailer? The numbers on the trailer plate decide how much you can legally put on it. Here’s what they mean, in plain English, for towing in Victoria.
The short version
- Legal carry capacity = ATM minus tare. A 750kg ATM trailer that weighs 250kg can carry 500kg.
- You can only tow as much as the lowest rating in the combination: the car, the towbar or the trailer.
- Over 750kg a trailer needs brakes. Over 2000kg it needs brakes on every wheel, worked from the driver’s seat, plus breakaway brakes.
Terms on the trailer plate
| Term | What it means |
|---|---|
| Tare | What the empty trailer weighs, ready to tow, with no load. |
| ATM (Aggregate Trailer Mass) | The most the trailer and its load can weigh in total, as set by the maker. This is the trailer’s legal maximum. |
| GTM (Gross Trailer Mass) | The most the trailer’s own axles can carry when it’s hitched up. It’s less than ATM because part of the weight sits on your towball. |
| GVM (on a trailer) | VicRoads registration papers often show the trailer’s maximum as “GVM”. For a trailer, read it as the same figure as ATM. |
| Carry capacity (payload) | ATM minus tare. The most load you can put on. |
| Towball download | The weight the trailer pushes down on your towball. Aim for about 10% of the loaded trailer. |
| GVM (tow vehicle) | The most your car or ute can weigh fully loaded, including the towball download. |
| GCM (tow vehicle) | The most your car and loaded trailer can weigh together. |
Why ATM and GVM get mixed up
On a car, GVM is the maximum loaded weight. On a trailer, the maker’s maximum is called the ATM, but Victorian registration papers and some older plates call the same thing “GVM”. If your rego papers say GVM, it’s normally the trailer’s total maximum. It’s never your car’s GVM, so don’t add the two together.
Working out carry capacity
Carry capacity = ATM − tare
- A 750kg ATM trailer that weighs 250kg can carry 500kg.
- A 750kg ATM trailer that weighs 500kg can only carry 250kg. Same ATM, half the load, because the trailer itself is heavier.
- A tandem trailer with a 2000kg ATM and a 650kg tare can carry 1350kg.
That’s why tare matters as much as size when you compare trailers.
Why our form starts at 500kg
Our lightest trailers weigh about 250kg. Built to a 750kg ATM (the most you can have without brakes), that leaves up to about 500kg of load. If you need to carry more, we’ll build a heavier-rated trailer with brakes and the right axles.
Towball download
Some of the trailer’s weight sits on your towball. A common guide is about 10% of the loaded trailer’s weight. For a 1500kg loaded trailer, that’s about 150kg.
- Too little download can make a trailer sway.
- Too much overloads the back of your car and the towbar.
- Never go over the towball download limit set by your car maker or towbar maker.
- The download counts towards your car’s GVM, so it eats into what you can carry in the car.
What you can tow: the lowest rating wins
Under Victorian law, the most a trailer can weigh when towed by a car or ute is the lowest of:
- the towbar’s rating (from the towbar maker),
- the car’s maximum towing capacity (from the car maker), and
- the trailer’s own ATM/GVM.
Also check your car’s GCM: the car plus the trailer must not go over it. A car rated to tow 3500kg can’t always tow 3500kg when it’s full of people and gear.
The towball, coupling and safety chains need to be rated for the loaded trailer as well. Not sure about your towbar? Ask us. We fit towbars every day.
Trailer brakes
Brakes are set by the national trailer rules (VSB1 and ADR 38). In short:
| Trailer weight (GTM) | Brakes needed |
|---|---|
| Up to 750kg | None required. |
| Over 750kg to 2000kg | Brakes on the wheels of at least one axle. Override (mechanical or hydraulic) brakes are allowed, and electric brakes are common. |
| Over 2000kg to 4500kg | Brakes on every wheel, worked from the driver’s seat (usually electric brakes with an in-car controller), plus a breakaway system that stops the trailer if it comes off. No override brakes. |
The rules are worded on GTM. In practice most people go by the ATM: if your trailer’s ATM is over 750kg, plan on brakes. Your car maker may also ask for brakes at a lower weight, so check the handbook.
Safety chains
- Up to 2500kg ATM: at least one safety chain, rated to Australian Standard AS 4177.4.
- Over 2500kg to 3500kg ATM: two safety chains to AS 4177.4.
- Over 3500kg ATM: two heavier, Grade T chains (AS 2321).
Cross the chains under the coupling and keep them short enough that the drawbar can’t hit the road if the coupling lets go. Use rated shackles.
Plates, VIN and registration in Victoria
- New trailers must have a 17-character VIN stamped on the drawbar or chassis and a metal trailer identification plate. For trailers up to 4.5 tonnes, the ATM and tare must be shown on the plate or on the trailer’s RAV record.
- A trailer being registered for the first time in Australia must be on the federal Register of Approved Vehicles (RAV).
- In Victoria, most trailers need to be registered and carry their own number plate. Up to 750kg ATM you use the light trailer form at VicRoads. Over 750kg up to 4.5 tonnes ATM, the trailer is inspected at VicRoads before it’s registered.
- A light trailer is one with an ATM of 4.5 tonnes or less. Heavier trailers come under heavy vehicle rules.
- Some trailers are exempt from registration. They show the towing vehicle’s number plate instead. Check VicRoads if you think yours might be exempt.
Every trailer we build comes with its VIN, plate and paperwork.
Weighing your load
You can’t see weight. If you’re close to the limit, weigh it.
- Use a public weighbridge (search “public weighbridge Ballarat”). Weigh the loaded trailer on its own, unhitched with the jockey wheel on the bridge, to check it’s under the ATM.
- Then weigh the car with the trailer hitched, and the car on its own, to check the towball download, GVM and GCM.
- Keep the docket. It’s handy if anyone asks.
Why overloading is a bad idea
- Safety: brakes, tyres, bearings, springs and the towbar are all sized for the rated weight. Overload them and stopping distances go up, sway gets worse, and parts fail.
- Fines: police and transport officers can weigh you and fine you for an overloaded vehicle or trailer, or going over a towing limit. You can also be told to stop and unload.
- Insurance: if you’re over a rated limit, your insurer may refuse a claim, for the car and for the trailer.
FAQ
Can I just fit bigger tyres or springs to carry more? No. The ATM is set by the maker and is on the plate. Changing it means re-engineering and new paperwork, not just new parts.
My trailer has no plate. What’s its ATM? Without a plate or paperwork you can’t be sure. Talk to us or VicRoads before you load it up.
Do I need brakes on a 750kg trailer? Not if it’s 750kg or less. Over 750kg, yes.
Can my car tow it? Check your car’s towing capacity and GCM in the handbook, and the rating on your towbar. The lowest rating wins.
How do I know what to tell you when I ask for a price? Just tell us roughly how much you want to carry. We’ll work out the trailer, ATM, axles and brakes to suit.
Get a price
Tell us what you want to carry and we’ll size the right trailer for the job.
This is a general guide. Rules can change, so check VicRoads or your vehicle and towbar maker’s figures before you tow.