Towing Weights Explained with Rules and Regulations

Posted on: 17/06/2019

Jacobs towing

 

Weight is a massively important consideration when towing, we simply cannot over-emphasise the gravity of the matter. It may not be something you've had to consider in the past, but every tow-vehicle and trailer are subject to weight limits – camper and vehicle manufacturers perform extensive testing to establish these limits. Rest assured, there is a safety margin beyond any given limit, to ensure owners don't inadvertently endanger themselves by packing on a few extra kilos.


Staying within manufacturer-specified weight limits, however, is not just a good idea, it's a legal requirement. It is possible to find yourself in some hot water if you're randomly weighed by state road authorities, or if you have an accident owing to an overweight load you will be held accountable and your insurance will be void.

 

TOW-VEHICLE

Your tow vehicle is crucial in determining the trailer-load you can haul. In the vehicle's manual, you'll find two weights that indicate its maximum towing capacity; braked and unbraked.

BRAKED refers to how much a vehicle can tow when trailer brakes are in use. This is most likely to be relevant to camper trailers.


UNBRAKED is legally restricted to 750 kilograms, some smaller trailers can come in below this limit.  


A third figure to take into consideration is the coupling download amount. This specifies the amount of downward force that can be exerted on a vehicle's towball. You may have heard that this will be 10 per cent of the overall towing capacity, but that's not always true. In particular, European cars can have a much lower download limit.

Axle capacities are also necessary considerations, particularly the rear. It's not all that common for campers to exceed their rear axle limit, although with the combined weight of the load packed into the vehicle and the force of the trailer coupling pushing downward it's possible.  

Finally, there's the gross combination mass (GCM). This is how much the entire rig weighs; vehicle, camper trailer and payload. The simplest GCM will be kerbside weight plus maximum payload and tow capacity, but once more this isn't a universal rule so make sure you know what yours is.

BARS, BALLS and COUPLINGS

Either inside the door jamb of your vehicle or fixed directly to the tow-bar you'll find a placard showing the maximum weight of the bar itself. These are generally the same as the vehicle tow weight, but not always, so it's best to double check. Similarly with tow balls and couplings, most are rated up to 3,500kg but you should always double check.

THE TRAILER

The weight of your camper comes in four flavours, which can generally be found on a placard on the A-frame or tucked away somewhere toward the front: Aggregate Trailer Mass (ATM), Gross Trailer Mass (GTM), tare weight and towball maximum.

Aggregate Trailer Mass (ATM) – the most your camper can weigh. It includes the trailer itself and everything in and on it. It is the combined total of the downward force exerted by the wheels and jockey wheel.

Gross Trailer Mass (GTM) – the maximum weight that the wheels can collectively impose on the ground. In other words, it's equal to the ATM minus the coupling download weight.

Tare Weight – the weight of the camper trailer as it leaves the factory. That means the tanks are dry and there are no dealer fitted extras. Subtracting the Tare from the ATM will give you the maximum payload weight (be aware that dealer fittings such as awnings and air-conditioners, as well as tank-loads eat into payload rates considerably, don't forget to include them into calculations when loading up).

Towball Weight – or hitch weight is listed on the compliance plate of modern trailers, but for older models it can be calculated by subtracting GTM from ATM.

If you're ever in doubt, the best way to check how much your rig weighs is to load it up to full trip weight and head to the nearest public weighbridge. When it comes to safety and legality, it's better to check and have your suspicions confirmed than to be proven wrong the hard way.

Brake controllers

These handy little devices allow allow drivers to control a trailer's braking system – you'll need one installed if you're towing more than 750 kilograms. They generally come in the form of an after-market attachment, which can be easily fitted with a little electrical know-how and a couple of zip ties. Their capabilities vary, but most modern versions will have smart sensors that detect how hard you're braking, as well as controlled modes for particular situations.