Towing 101: what to know before you tow

An Isuzu D-Max 4WD ute towing a caravan

Toby Hagon

Posted January 28, 2022


Everything from tow balls, torque, trailers and tyres - there’s a lot more to know about towing that you need to know before you hit the road.

While being able to tow a trailer, caravan, or boat is one of the greatest conveniences a car can offer you, the consequences can be deadly if you don’t know what you’re doing.

The dangers of navigating a service station forecourt or a fast-food carpark is nothing in comparison to the dangers of a poorly-connected trailer while travelling 100km/h down the freeway.

Here is everything you need to consider before, during, and after you connect anything to your vehicle.

Consider what’s doing the towing

Forget power, it’s torque that does all the work when you’re towing.

That’s why so many people turn to diesel engines for towing heavy loads. Modern turbo diesels can produce plenty of grunt without needing to rev too hard - making them ideal for hauling heavy loads.

If you’re looking to tow very heavy loads over big distances it’s worth considering something with a bit more grunt. Check out the specifications and make sure you’ve got at least 400Nm of torque; anything approaching 500Nm is even better. More than that is a bonus and will make much lighter work of towing.

Check out our article on the best cars for towing a caravan for specifics on what cars to consider.

A Toyota Prado towing a caravan on a dirt road

Towing is a complex issue for caravan, boat and horse-float owners.


Understand the jargon

There’s an assortment of jargon, acronyms and numbers associated with towing.

The most obvious is the ‘maximum tow capacity’, which is what a car can legally – and safely – tow. Exceeding that limit not only risks a fine, but could also damage the vehicle or contribute to a crash.

Then there’s the ‘down weight’ or ‘tow ball download’, which is the maximum weight that can be pushing down on the tow ball when the car is parked on a level surface. Most of the time you want about 10 per cent of the weight of the trailer pushing down on the hitch; there are scales for measuring it.

The ‘gross vehicle mass’ (GVM) is how much weight the car can take, including the weight of the car and whatever you pack into it, including people, luggage, and fuel.

When calculating the GVM for towing, you need to take into account how much downward weight the trailer is exerting on the rear of the car. If you have 350kg pushing down on the tow hitch, then you have to take 350kg off the payload of the car.

Next comes the ‘gross combination mass’ (GCM), which is the weight of the car and the trailer and everything in each of them.

Dig deeper than the maximum tow capacity

Just because a car or ute says it can tow 3.5 tonnes doesn’t mean it can – at least if you want to take the family and all your gear with you.

Once you take into account all those other limits, some tow vehicles will only let you carry a few hundred kilograms, possibly less. While you also have to consider things such as the maximum axle load – ensuring you’re not overloading one end of the car – it’s also crucial to calculate GCM and GVM for your towing setup; either one can limit your payload.

 

Isuzu D-Max towing a caravan in regional Australia

Torque counts when towing large caravans.


Crunching the numbers

The Toyota Prado gets a huge 150-litre fuel tank so is great for towing without having to stop every few hundred kilometres to refuel.

But if you want the leather-clad Kakadu model you can only put 340kg in the car once you’re towing the maximum 3000kg it’s rated for. That’s 340kg in total for people, luggage, camping gear, food and water.

The just released Toyota LandCruiser 300-Series has a tow capacity to 3500kg. But the vehicle itself weighs up to 2630kg and with a gross vehicle mass limit of 3280kg it means you can only carry 300kg of people and gear when towing that max amount (accounting for the 350kg pushing down on the tow ball).

Impressed by the 3500kg tow limit of the new Isuzu MU-X? Don’t get too excited, especially if you choose the top-of-the-line LS-T 4x4 model. It has a GCM limit of 5900kg, so once you’ve got 3500kg of trailer on top of the 2175kg for the car itself then you can only put 225kg of people and luggage in the cabin. You might be able to make that work as a couple if you pack carefully and cut back on the biscuits and cakes, but you certainly won’t be bringing the kids along.

Consider a car with a higher towing limit than you’re ever likely to use, so it doesn’t constrain you in other areas.

Bringing it all to a stop

Anything over 750kg requires the trailer to have its own braking system, both to adhere to the law and to reduce the strain being put on the braking system of the tow vehicle.

Up to 2000kg you can have mechanical brakes, which activate a piston or cable when the trailer pushes against the car.

Over 2000kg you need electronic trailer brakes, which can ‘talk’ to a brake controller in the car.

You can adjust the brake bias – or how aggressively the trailer brakes compared with the car – and independently apply the trailer brakes to control trailer sway.

 

A Land Rover Discovery hauling a retro-styled caravan

If you are towing over two tonnes, electronic brakes are a must.


You’re ready to roll

Be aware that the car will be slower and use a lot more fuel when towing. Blame physics.

It’ll also take longer to stop and behave differently over bumps, so drive accordingly.

And best to get used to your rig before joining the holiday rush. At the very least, practice reversing with a trailer before hitting the Maccas carpark. It could save some red faces.

 

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