Legal Braking Requirements NZ & AUS

NZ Braking Regulations

Up to 2000kg GVM

In New Zealand the braking requirements for trailers are pretty simple. For up to 2000kg load capacity or GVM (Gross Vehicle Mass which is the trailer weight and its load combined) there is no legal requirement for brakes. The law states that the tow vehicle and trailer must be able to stop safely within 7 metres from 30km/hr safely.

The biggest consideration that needs to be taken is the tow vehicle's legal tow rating.

If it is only certified or recommended that the tow vehicle is rated to 750kg GVM unbraked (check your vehicles handbook for specs) then it is unwise to tow an unbraked trailer exceeding 750kg GVM. Just remember that you could be charged with dangerous driving if you are caught or have an accident, incurring serious penalties as well as possibly voiding your insurance.

If you are unable to determine the towing capacity of your tow vehicle, either check with your local towbar manufacturer, go online and check your vehicles specifications, or as a rough guide set out by the NZ Transport Authority use the following – “the laden weight of an unbraked trailer should not exceed three quarters of the unladen weight of the towing vehicle and then only if the towing vehicle's brakes and tyres are in excellent condition. A trailer heavier than this may prevent the vehicle combination from meeting the seven metre for 30km/hr brake performance requirement.

2000 to 2500kg GVM

Between 2000 and 2500kg GVM trailers must be braked on at least one axle via either override brakes (hydraulic coupling unit) or with cab controlled brakes (more on this later) and again must be able to stop within 7 metres from 30km/hr. Dual crossed safety chains (see below) or an electrically operated breakaway system is also required. Both coupling and chains are required to be rated and marked.

With the crossed chain system, if for whatever reason the trailer detaches from the tow vehicle, the chains will support the coupling end of the trailer, and give you some semblance of control until you are safely off the road. You may get a bit of damage to the rear of your vehicle as the trailer shunts into it, but better to have a small repair bill than having your wayward trailer crossing the road and injuring or killing someone! Don't be lazy when fitting your double chains - always cross them and if you do not have two mounting points on your tow bar, get another one fitted.

Over 2500kg GVM

Trailers with a GVM over 2500kg up to 3500kg need some serious braking power and must be fitted with cab controlled brakes (direct braking). The trailer is also required to be fitted with a breakaway system (more on this later) and a parking brake on at least one axle which can sustain the trailer and load in position on a slope of 1 in 5 (approx. 20 degrees).

Again the stopping within 7 metres at 30km/hr rule still applies. Safety chains are not required although personally I like to have one fitted for peace of mind. Unless you have some very serious axle and braking hardware under the trailer you will need to have brakes on both axles.

A note about imported trailers from the EU - It is possible to import a certified, 3500kg rated trailer from the European Union and apply for exemption from the above ruling for cab controlled brakes. Almost all European Union manufactured trailers operate mechanical drum brakes via an override coupling setup and an application to the NZTA for exemption for non-compliance of the standard can be applied for. According to the NZTA, if a trailer cannot be modified to comply with the braking regulations then application for exemption can be undertaken.

I have yet to form a balanced opinion on this anomaly of the regulations!

Over 3500kg GVM

Over 3500kg GVM falls into the realm of Heavy Transport regulations and for the most part is beyond the scope of this website. The rules are complex and change on a regular basis. Certification is required on almost every aspect of the trailer and requires professional engineering input from the start, and unless you have very deep pockets, I would look at other options before progressing down this path.

Indirect Braking

Indirect braking is a braking system which uses the weight of the towed trailer to operate the brakes via inertia through a spring dampened override coupling. The movement of the coupling applies the brakes proportionate to the amount of travel of the spring. This inertia can be applied to mechanical and hydraulic disc and drum brakes.

The advantages of indirect braking is that everything required for braking is self contained within the trailer which means any vehicle can tow the trailer. It is also relatively cheap and reliable.

The disadvantage is that the trailer brakes can activate while reversing and unless the coupling is fitted with an automatic reversing solenoid (which electrically disconnects the brakes), you will need to get out of the tow vehicle and engage a lever to prevent the brakes from working while reversing. This leads to the risk of accidents if the lever is not disengaged before driving forward again.

Newer style European override couplings do away with the spring dampened coupling and work on a hydraulic damper system which does give better and more reliable braking including automatic reversing control.

You can use a trailer mounted brake controller to operated electric drum brakes. This involves adjusting a knob on the controller to the amount of weight you are carrying on the trailer. When the tow vehicle brakes, the controller activates via the tow vehicle's brake lights and sends an electric current to the drum brakes proportionate to the amount set on the knob.

This can be a little hit and miss with the adjustment and requires a bit of trial and error to get right.

Direct Braking

Direct braking is braking the trailer with full control from the tow vehicle including emergency override braking.

There are many systems available and the most commonly used is to wire a dedicated tow vehicle with a cab brake controller. The controller uses an electrical inertia pendulum which senses the movement of the tow vehicle. If the tow vehicle slows or brakes, the controller will send a signal to the drum brakes to brake proportionately. The controller is adjustable to the amount of weight being carried on the trailer and can be adjusted whilst driving. This gives better control down steep hills and on gravel where skidding and jack knifing of the trailer could occur.

Every trailer parts supply company has their own type of controller or system for direct braking and new systems are coming out on a regular basis. The simpler but less convenient systems are normally reasonably priced and the more complex but more convenient systems can set you back a small fortune.

Breakaway Brakes


Breakaway brake units are designed to immediately apply full braking power to the trailer brakes should the trailer separate from the tow vehicle.

On electric braked trailers, the breakaway unit is basically a on/off switch box fitted with a removable pin which is attached to a tether cable.

The box is mounted on the trailer drawbar and the tether fitted to the tow vehicle with a shackle or hook.

A small rechargeable battery on board the trailer supplies power to the breakaway box and when the pin is pulled from the box (when the trailer comes away from the tow vehicle) full power is instantly applied to the brakes.

Power is supplied to the brakes until the on board battery runs out of juice or the pin is re-fitted to the breakaway box.

It does pay to regularly check the battery charge especially when the trailer is infrequently used. If this is the case, remove the battery and charge it on a mains charger before any trips. Also check that the tow vehicle is charging the battery when plugged into the trailer.

To check if the breakaway unit and battery are working correctly, immobilize the trailer and jack the wheels up. Pull the breakaway pin while a mate spins the wheels. They should lock up immediately.

The breakaway tether needs to be attached to the tow vehicle and not to the chains, the chains will not pull the breakaway pin out if the trailer decides to part company. Likewise the tether needs to be in good condition and needs to be replaced if kinked, frayed or damaged. If the damaged section fails before the breakaway pin can be pulled, the brakes will not come on.

Breakaway brakes should not be used as a park brake as the battery will quickly lose its charge and the brakes will release.

Australian Braking Rules

Light trailer braking regulations in Australia for trailers up to 4500kg ATM are relatively straight forward

Up to 750kg GTM

Trailers with a 750kg GTM (Gross Trailer Mass) do not require brakes but do require a least one safety chain that is rated and complies with AS 4177.4-1994 or AS 4177.4-2004 and have shackles to match.

750kg up to 2000kg GTM

Trailers over 750kg GTM up to 2000kg GTM, must have working brakes on at least one axle. Over-run or surge brakes (see indirect braking above) can be used up to 2000kg GTM and the trailer must have at least one rated chain or cable as per the standards above.

2000kg to 2500kg

For all trailers over 2000kg GTM, all wheels must have operational brakes. Over-run or surge brakes are not permitted. Independent Electric Brakes or power assisted hydraulic brakes are allowed. These must be driver controlled by either hand or foot. A breakaway brake system is required to be fitted (see above). If the trailer does detach from the towing vehicle, the brakes must remain applied for at least 15 minutes.

Over 2500kg ATM

For all trailers over 2500kg ATM up to 4500kg ATM, all wheels must have operational brakes. Over-run or surge brakes are not permitted. Independent Electric Brakes or power assisted hydraulic brakes are allowed. These must be driver controlled by either hand or foot. A breakaway brake system is required to be fitted (see above). If the trailer does detach from the towing vehicle, the brakes must remain applied for at least 15 minutes. Up to 2500kg ATM, the trailer must be fitted with at least one rated chain or safety cable as per the standard above.

Over 2500kg and up to 3500kg ATM, the trailer must have two rated safety chains as per the standard.
Trailers over 3500kg up to 4500kg ATM need two safety chains with a minimum breaking stress of 800MPa and must conform to the mechanical properties of a Grade T chain (short link lifting chain) and must be sized so that the minimum breaking strain exceeds 4500kg ATM.