Towing a camper trailer is not just a simple process of hooking up and taking off for your favourite camping spot. As a duty of care to other road users there are a number of rules and guideline limits you need to be aware of, otherwise you could be breaking the law, voiding your vehicle warranty or insurance in the event of an accident.

A vehicle and camper trailer must compliment each others maximum capacities making for a safe combination in all situations. This especially applies to lighter vehicles and soft roader 4wds which have lighter tow capacities. If the ball weight is too heavy, the tow vehicle's rear suspension will be forced down affecting braking and also the vehicle’s steering when it is most needed, typically during an emergency situation.

the law

In December 1998, an agreement was reached by all state Ministers of Transport to implement a national towing regulation. One rule, put simply, says the most you can tow is the amount specified by the vehicle manufacturer or the capacity of the tow bar - WHICHEVER IS THE LESSER.

In the case where a motor vehicle manufacturer has not specified a maximum towing weight or capacity, the towing limit is 1.5 times the unladen or kerb weight of the motor vehicle if the trailer is fitted with brakes or the unladen weight of the motor vehicle if the trailer is not fitted with brakes.

camper trailer capacity

he maximum weight a camper trailer will carry is called the Aggregate Trailer Mass (ATM) and is specified by the trailer manufacturer. The ATM is the total mass of the laden trailer when carrying the maximum recommended load over the “axle group” and also includes any mass imposed onto the drawing vehicle (ball load).

The maximum weight a camper trailer will carry over the “axle group” is called the Gross Trailer Mass (GTM) and is also specified by the trailer manufacturer.

These weights (ATM and GTM) are determined by the trailer manufacturer and are based on a number of factors. These factors include chassis strength, maximum axle capacity, suspension capacity, tyre size and rating, bearing size and “A” frame design. Off-road camper trailers are built heavier than on-road camper trailers, mostly for weight carrying strength and ruggedness in the harsh outback conditions. A camper trailer manufacturer would have taken these considerations into account during the design and fabrication process.

drawbar

The National Code of Practice booklet ‘Building Small Trailers’, also commonly referred to as Vehicle Standards Bulletin 1 or VSB 1, is available from motor registry offices or can be downloaded from the following website: www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/vsb1/

VSB 1 requires that drawbars must withstand the following forces applied at the centre of the intended coupling without detachment or any distortion or failure, which will affect the safe drawing of the towed trailer:

Longitudinal tension and compression (N) - 1.5 x 9.81 x ATM (kg)
Transverse thrust (N) - 0.5 x 9.81 x ATM (kg)
Vertical tension and compression for rigid drawbar trailer (N) 0.5 x 9.81 x ATM (kg)

towbar

A tow bar must be stamped by the tow bar manufacturer with both maximum allowable ball weight and maximum allowable towing weight. If you are unsure as to how strong the tow bar is, have a chat to a reputable towing equipment specialist.

coupling

The coupling must be marked in accordance with ADR 62/…and includes the manufacturers name or trademark and the maximum rating for the coupling body. Further information can be obtained in VSB 1.

brakes  

A camper trailer must be fitted with brakes if the trailers weight including its load exceeds 750kg. There are different types of brakes available such as mechanical overriders, hydraulic overriders, electrically operated hydraulic and electric. An electric brake controller must be placed within easy reach of the drivers seat.

Trailers that do not exceed 750 kgs. (0.75 tonne) GTM with a single axle do not required brakes.

Note: Two axles with centres spaced less than one metre apart are regarded as a single axle.

All other trailers that do not exceed 4.5 tonnes ATM must be fitted with an efficient brake system that complies with Australian Design Rule (ADR) 38/...

Except for over-run brakes, all brakes must be operable from the driver's seat of the towing vehicle.

For trailers up to 2 tonnes GTM, an efficient braking system is considered to have brakes operating on the wheels of at least one axle. Over-run brakes may only be used on trailers that do not exceed 2 tonnes GTM.

Every trailer over 2 tonnes GTM must have brakes operating on all wheels. The brake system must cause immediate application of the trailer brakes in the event of the trailer becoming detached from the towing vehicle. Under these circumstances, the brakes must remain applied for at least 15 minutes.

ball weight

In a perfect world of smooth flat roads, a 5% ball weight would be ideal. However, undulating roads and potholes or strong crosswinds into the equation producing negative ball weights, can have serious effects on the vehicle and camper, causing the combination to become out of control.

The 10 to 15% rule of thumb ball weight of a fully loader trailer gives a safety net and some room for error, particularly when it comes to a camper trailer with weight shifting quantities. These weights can vary greatly, either forward or to the rear of the axle, as jerry cans of fuel and water are used, the water tank is emptied, firewood unloaded or food is consumed.

Ball weight can be affected by a number of factors which can quickly overload the front of your camper. The “A” frame can be used to store an outboard motor, toolbox with tools and other heavy gear, a spare tyre, gas bottles, fuel or water jerry cans and a fridge packed with food. Attention to the 'balance' of the camper needs to be maintained, keeping the ball weight within permissible limits and the calculated strength of the drawbar.

know before you go

It is a good idea for a camper trailer owner to weigh his fully laden or loaded camper at least once on a weighbridge so he knows what the camper and ball weight is. This will help with future packing of the camper. Check the yellow pages under public weighbridge for location of weighbridges. For the few dollars it will cost to weigh the trailer, you will have piece of mind.

calculating the ball weight

First, place the loaded camper trailer, unhitched, with its jockey wheel and wheels on the weighbridge to give you the ATM.

Now, with the camper trailer hitched to the tow vehicle and with only the camper trailer’s wheels on the weighbridge, this will give you the GTM.

The difference between the ATM and GTM will give you the ball weight.  A ball weight of around 10% to 15% gives a fully laden or loaded trailer good forward balance.

vehicle weight limits

A vehicle manufacturer sets maximum weight capacities such as Gross Vehicle Mass, Tare and ball weight. It is important you do not exceed these limits.

The Gross Vehicle Mass (GVM) is the Tare weight of the vehicle plus accessories like bullbars, roofracks and rear drawers. It also includes a payload such as cargo, fuel, the driver and passengers, plus the ball weight of the trailer.

Some vehicle manufacturers have a reduced towing capacity when towing off-road. If you want to know how much your vehicle can tow, check the owner’s manual or your vehicle’s sales brochure for the manufacturer’s permissible towing recommendations. Make sure the vehicle’s maximum towing capacity is more than the trailer weight, including its load. Some vehicle manufacturers also have a maximum tow capacity when used off-road, which is usually far less than the on-road maximum. 

a balanced rig

The vehicle is fitted with a bullbar and winch, 70 litres of fuel, fridge, misc gear & two people which gives the vehicle a total loaded weight of 2360kg. In this situation as set out below, you are only permitted to add 140kg ball weight to the vehicle to reach the vehicle manufacturers 2500kg GVM capacity.

vehicle manufactures max specs		vehicle manufactures max tow specs
Gross Vehicle Mass - Tare - max payload -	2500kg 2000kg 500kg	Gross Trailer Mass on road - Gross Trailer Mass off road - ball - not actual manufacturers figures	2300kg 1000kg 170kg

vehicle weights		camper weights
steel bullbar & winch - two people - 70 litres of fuel - fridge & misc gear - payload - Tare -  -------- total weight -	60kg   180kg     70kg     50kg + ----------------   360kg 2000kg + ---------------- 2360kg	camper weighs - actual ball weight -      figures just to explain the scenerio	1200kg 130kg
allows for 140kg ball weight on the vehicle

terms

Tare Mass - mass of a vehicle, other than a L-group vehicle (motor cycle), ready for service, unoccupied and unladen, with all fluid reservoirs filled to nominal capacity except for fuel, which shall be 10 litres only, and with all standard equipment and any options fitted.

Camper Trailer Tare Weight - is the weight as it left the manufacturer (with all options fitted) and is usually the weight without water in the tanks or gas bottles filled.

Laden Mass - the mass of a vehicle and its load borne on the surface on which it is standing or running.

Unladen Mass - the mass of the vehicle in running order unoccupied and unladen with all fluid reservoirs filled to nominal capacity including fuel, and with all standard equipment.

GVM - or Gross Vehicle Mass is the maximum laden mass of a motor vehicle as specified by the ‘Manufacturer’.

GTM - or Gross Trailer Mass is the mass transmitted to the ground by the ‘Axle’ or ‘Axles’ of the trailer when coupled to a drawing vehicle and carrying its maximum load approximately uniformly distributed over the load bearing area, and at which compliance with the appropriate Australian Design Rules has been or can be established.

ATM - or Aggregate Trailer Mass is the total mass of the laden trailer when carrying the maximum load recommended by the ‘Manufacturer’. This will include any mass imposed onto the drawing vehicle when the ‘Combination Vehicle’  is resting on a horizontal supporting plane.

GCM - or Gross Combined Mass is the value specified for the vehicle by the ‘Manufacturer’ as being the maximum of the sum of the ‘Gross Vehicle Mass’ of the drawing vehicle plus the sum of the ‘Axle Loads’ of any vehicle capable of being drawn as a trailer.

Manufacturer - the name of the person or company who accepts responsibility for compliance with the Australian Design Rules and to whom the ‘Compliance Plate’ approval certificate is issued.

Load Capacity - the difference between ‘GVM’ of the vehicle and its ‘Tare Mass’.

Payload of a vehicle includes the occupants and cargo as well as any accessories such as bull bar, tow bars, winches, roof racks and also includes the ball weight of the trailer.

Recommended Ball Weight is the maximum allowable weight permitted to be placed on the vehicle’s tow ball as recommended by the tow bar manufacturer.

Axle Load - total load transmitted to the road by all the tyres of all the wheels whose centres may be included between 2 transverse parallel vertical planes less than one metre apart.

Axle Group - either a ‘Single Axle’, ‘Tandem Axle Group’, ‘Triaxle Group’, or ‘Close Coupled Axle Group’.

Axle - one or more shafts positioned in a line across a vehicle, on which one or more wheels intended to support the vehicle turn.

by Rob

thanks to Alan Everingham for his input

 

november 2011

updated july 2015