What is braked towing capacity?

Q: What is braked towing capacity, and what does braked towing capacity mean in the real world?

A: Braked towing capacity is the upper limit that your vehicle can tow without breaching safety, mechanical, legal or insurance boundaries.

As the name suggests, it relies on the towed load (trailer, caravan, boat-trailer) having its own brakes so that the combination is not reliant solely on the tow-vehicle’s brakes to slow or stop.

This figure is the absolute upper limit of what a particular make and model can legally tow.

Braked vs unbraked towing is an important distinction as the limits for either are very different. Unbraked towing capacity which – again as the name suggests – is how heavy a load you can tow on a trailer without its own brakes (therefore relying on the towing vehicle for all slowing and stopping duties). It’s nearly always a lot lower than the braked limit.

It’s important to understand braked towing capacity and not exceed it, for a variety of reasons, starting with staying within the law.

If you exceed the towing vehicle’s braked towing limit, you’ll be unroadworthy and you could be fined even if there’s no incident.

This also has insurance ramifications, and your insurer might walk away from you in the case of a crash involving a car that was towing too heavy a load.

You’ll also void your car’s warranty by exceeding this limit as well as placing stresses and strains on the vehicle it was never designed to cope with. Brakes, clutches, tyres, transmissions and engines can all suffer from too much load on them.

Braked vs unbraked towing is an important distinction as the limits for either are very different. (Image: Sam Rawlings)

The crucial measurement in any assessment of braked towing limit is the mass of the trailer and whatever is loaded on it. This mass is what the police will measure if they think you’re over the limit. You can measure this mass yourself with a public weighbridge.

Many councils now have weighbridges at recycling stations and, for a small fee, you can weigh your trailer either empty or loaded. By weighing the trailer empty, you’ll then have a reference number for how much you can load on to it before it exceeds the car’s towing limit.

The other option is to use a set of towball scales that measure the amount of weight you’re putting on the car’s towbar, and there are now wireless, Bluetooth trailer scales that are placed under the wheels and the total mass added up for you.

There are also plenty of online caravan weight calculator pages where you input all your known data and the website works out if your car is big enough for the job or whether you’re overloaded in any department.

Just be sure to search for something like 'vehicle towing capacity calculator Australia' to ensure you find one that’s relevant to our local laws and limits.

Terms you’ll find handy to know for this are Aggregate Trailer Mass (ATM) which is the total mass of the trailer when carrying the maximum load that the manufacturer recommends for that trailer or caravan.

If you exceed the towing vehicle’s braked towing limit, you’ll be unroadworthy and you could be fined even if there’s no incident. (Image: Deon Rowe)

This is measured with the trailer disconnected from the towing vehicle and resting on its jockey wheel. This figure is determined by the trailer’s manufacturer and should never be exceeded.

The other term you need to know is Gross Trailer Mass (GTM) which is the mass of the trailer when it’s hitched to your tow vehicle (and some of the mass is distributed through the tow-ball into the tow-car).

Both these numbers are calculated by the trailer maker and are non-negotiable. There’s also a big difference between the allowable gross trailer weight braked and unbraked. That’s true of the tow-car, too, manufacturers have very different limits on towing not braked and with brakes.

The empty trailer’s mass is what’s known as its tare mass. The difference between this number and the ATM for your trailer is the trailer’s payload capacity.

At the moment in most Australian states and territories, there’s no simple, legal method of increasing a car’s towing capacity or a trailer’s loaded capacity.

The trailer manufacturer will have their own method of how to measure capacity, just as carmakers have their own formulas for calculating maximum towing capacity.

Brakes, clutches, tyres, transmissions and engines can all suffer from too much load on them. (Image: Brendan Batty)

The towing vehicle’s braked towing limit, then, is not something you need to measure or calculate yourself. The number has already been determined by the vehicle’s manufacturer based on engineering and is not negotiable.

You’ll find this info in the owner’s handbook. Neither is there an aftermarket package that can lift your braked towing limit. If you need to tow heavier loads, you need a bigger, heavier car that can do so. What is towing capacity in the handbook is the only number the authorities will be concerned with.

Trailer brakes themselves come in two main forms. The simplest is the mechanical brake which uses the weight of the trailer to actuate the brakes via a mechanical or hydraulic link.

As the tow-vehicle slows, the trailer tries to maintain its speed (basic physics at work) and the mechanical linkages are brought into play by the resulting force.

Electric brakes are more complex but a more refined, sophisticated and efficient solution. The tow car is fitted with a sensor that, when it detects the brake pedal is pushed, sends an electrical signal back to the trailer which then applies the trailer’s brakes. You can fine-tune the amount of braking the trailer contributes on the run, making this a better system.

To help put all this into context, here’s a quick run down of the typical braked and unbraked towing limits of popular types of vehicle:

Dual-cab ute (Toyota HiLux 4X4): 3500kg braked, 750kg unbraked.

4X4 wagon (Nissan Patrol): 3500kg braked, 750kg unbraked.

Large SUV (Hyundai Palisade): 2200kg braked, 750kg unbraked

Medium SUV (Mazda CX5): 1800kg braked, 750kg unbraked

Be aware, however, that even within specific model ranges, details such as whether a vehicle is two- or four-wheel drive, and whether it’s petrol or diesel powered can also have an effect on those mandatory limits.

Electric and hybrid cars often have much lower towing limits, too. So check each car out individually before making any decisions.