Trailer laws explained

Getting the caravan or camper trailer to and from the campsite opens up a whole new world of regulation, and unfortunately, you’ll have to get your head around the rules to stay legal in all States.

Sorting out the towing rules and regs isn’t child’s play. We’re still waiting for responses from the ACT and Tasmania, while the NT’s efforts were lame.

However, many of the towing mistakes made by caravanners are elementary and stem from not knowing the terminology.

TOWING TERMS
First, you’ll need to learn weight definitions that are crucial for towing legally. So let’s start by getting the terminology right so we’re all on the same (and legal) page.

Tare mass (TM) is the mass of the trailer unladen, as it leaves the factory, ready to be registered and used. TM does not include water, gas or options fitted (except factory-fitted options).

Gross Trailer Mass (GTM) is the mass that can be carried by the trailer’s wheels, with everything on the trailer (camp chairs, food, bed sheets, etc).

Tow Ball Mass (TBM) is the amount of the trailer’s mass imposed on the towball of your tow vehicle.

Aggregate Trailer Mass (ATM) is the combination of GTM and TBM. Imagine your caravan, all loaded up but sitting on its jockey wheel — that mass sitting on the road is ATM.

KNOW YOU RIG’S WEIGHT
Say your trailer has a 2500kg Tare or TM, 3250kg GTM and 3500kg ATM. Subtract Tare from ATM, and you’ve got your maximum payload figure — 1000kg in this case.

If your caravan and everything in it weighed exactly 3500kg, you would have to have at least 250kg on the towball, because you can’t exceed the GTM figure in this hypothetic scenario of 3250kg.

Be aware that if you add extras to your van (such as a bike rack) that weight including the bike(s) will become part of your payload.

The trailer compliance plate (for all trailers built since August 1989) will give rated maximums for both GTM and ATM, and in some cases TBM.

The only way to really know what your van or camper weighs is to load it up as you normally would and put it over a public weighbridge. It might be the best $30 you spend.

TOW TUG AND TOW BAR
You need the right tow vehicle and towbar. Both the vehicle and the towbar should have a plate or sticker noting maximum permitted towing mass figures, both for total towing mass and TBM (the vehicle towing capacities are usually on a sticker fitted to a door jamb. If not, these specifications will be in the owner’s manual).

If you bought a used vehicle with a towbar already on it, check that towbar capacity matches the vehicle’s towing capacity. Some don’t: for example the VFII Commodore can tow 2100kg but Holden offers a choice of 1200kg, 1600kg or 2100kg towbars for the VFII. Check the towball too: if you’re towing 3500kg then a 2000kg-rated towball is no use to you.

A vehicle’s legal TBM maximum is usually 10 per cent of its towing capacity: for example, with a 3500kg towing capacity, you’d be able to plonk up to 350kg of that on the towball. It’s not always as much as 10 per cent though, particularly with some Korean and European vehicles. You might find such a vehicle has 2500kg towing capacity but just 100kg maximum TBM.

VEHICLE WEIGHT
Vehicle weight maximums include kerb mass, axle mass, Gross Vehicle Mass and Gross Combined Mass.

Subtract kerb mass from GVM and you have your payload — that’s the weight of everything in and on your vehicle (kerb mass always includes the vehicle’s fluids and depending on the manufacturer, a full tank of fuel and weight of a driver, which the manufacturer will stipulate in the owner’s manual).

TOWING SPEED LIMITS
Before you even get to the state-by-state rules on towing speed, there are some vehicle manufacturers that cap maximum speed when towing. For Subaru, for example, it’s 80km/h.

In Queensland, NSW, Victoria, NT, SA and the ACT you can drive at up to the prevailing speed limit when towing (up to 110km/h).

In WA and Tasmania, the maximum legal towing speed is 100km/h, where permitted, while in NSW you’re restricted to a maximum of 100km/h if your combination’s GCM is more than 4500kg.

TRAILER BRAKES
Between 750kg-2000kg GTM, trailer brakes are necessary, but they can be override brakes and only need to activate on one axle.

With a GTM of between 2000kg-4500kg, the trailer must have brakes on all axles that can be controlled by the driver in the cabin. That means electric/hydraulic brakes for most vans operating in this weight range.

The trailer also must have a break-away braking system, which automatically activates the trailer brakes if it becomes decoupled from the vehicle. In NSW, it’s also a legal requirement to have a break-away battery monitor placed in view of the driver.

Once you reach 4500kg GTM, you’re into heavy vehicle class and will need a more sophisticated braking system such as air brakes.

SIZE RESTRICTIONS
Under VSB1 (the national standard applying to trailers), a trailer has to measure no more than 4.3m high and its rear over hang must not be more than 60 per cent of the wheelbase measurement (coupling to wheelset) or 3.7 metres, whichever is the lesser.

Maximum trailer width is 2.50m nationwide, which is fine for most Aussie and even imported vans (but can put owners of some US boats over the limit). The rules are slightly different in each state when it comes to towing over-width trailers.