Toyota Prado
Toyota Prado

Guide to what you really need to know before towing

THE holiday hordes are back at work, so if you're one of the lucky people not joining them, now is an ideal time to hit the road - for a cruise along the coast or something more ambitious such as a lap of the wide brown land.

All you have to do is hitch up the caravan and take off, right?

There’s a hitch: There are rules to follow and mistakes to avoid
There’s a hitch: There are rules to follow and mistakes to avoid

Not quite. Some things in life on face value should be pretty straightforward - delve deeper and they're anything but. Welcome to the dark and mysterious world of towing.

How difficult can it be? How many rules can you have for the simple act of dragging a trailer around? Surely you just buy a trailer or caravan that's within your vehicle's towing capacity?

The answers, in order, are: it's more difficult than you think; lots; and no.

Mistakes can be painful, expensive and illegal. Here's what you need to know.

 

IT'S ALL ABOUT THE MATHS

Your most important tool when deciding what tow vehicle, van or trailer to buy is a calculator, and your most important references are manufacturers' specifications.

You need to do the numbers to make sure you comply with all weight limits, because if you have a crash and need to make an insurance claim, the first thing the insurance company will do is check. If you're overweight, you're illegal, so your claim can be rejected.

Within specification: Vehicle, trailer and load must not exceed complex limits
Within specification: Vehicle, trailer and load must not exceed complex limits

You can also be charged with a range of serious traffic offences, depending on which state you're in.

Towing is governed by a complex web of maximum weight limits, primarily gross vehicle mass (GVM), gross trailer mass (GTM) and gross combined mass (GCM). See below, Towing Decoded.

 

DON'T TAKE A MAKER'S CLAIM AS GOSPEL

Manufacturers' maximum towing weight claims are usually meaningless and you believe them at your peril. It's ridiculous that makers can claim figures far in excess of the legal maximum that their fully laden vehicles can actually tow - but it's common practice.

The legal maximum weight for your vehicle and trailer, hitched together, must be less than the combined, individual legal maximum weights for the vehicle and trailer.

Technically speaking then, gross combined mass must be less than the sum of gross vehicle mass and gross trailer mass.

Surely it's a case of one plus one equals two? Not on Planet Towing, it's not.

Toyota HiLux SR5: All-up weight limit is 5650kg
Toyota HiLux SR5: All-up weight limit is 5650kg

We'll do a calculation using the top-selling Toyota HiLux SR5 automatic to illustrate the intricacies. For the figures on other popular utes and SUVs, see below - How Much Can They Really Tow?

The HiLux's legal maximum gross combination mass is 5650kg. Its gross vehicle mass of 3000kg, plus its maximum claimed towing capacity of 3200kg, equals 6200kg - which is 550kg more than its legal maximum gross combined mass.

We're assuming here (and in the other vehicles listed) that the HiLux is fully loaded to its GVM, which includes 955kg of payload.

If you're buying a tow vehicle, look at its maximum gross combination mass. Deduct its gross vehicle mass. If you want to play it safe with a reasonable buffer for payloads, treat this weight as what you can safely and legally tow.

It will almost always be less than the manufacturer claims.

In the HiLux's case, you subtract its 3000kg GVM from its 5650kg GCM, which leaves you with 2650kg to tow.

If you're buying a trailer, deduct its aggregate trailer mass (ATM) from your tow vehicle's gross combined mass.

If the result is significantly less than your gross vehicle mass, you need to choose a lighter trailer, or a new tow vehicle.

Again using HiLux, if you're looking at a trailer with an ATM of 3200kg, subtract that from the GCM (5650kg) and you're left with 2450kg - or 550kg less than HiLux's actual GVM.

You can check your weights at a public weighbridge.

 

THEN THERE'S TOWBALL DOWNLOAD

Is 10 per cent towball download the legal maximum? No. Up to 15 per cent is acceptable.

In NSW, Roads and Maritime advises a download of 5-10 per cent. In Europe, the legal maximum is a mere 75kg, no matter what the weight of the trailer.

If you exceed 10 per cent, you might need a weight distribution hitch to keep the outfit level - but then you get into the thorny issue of warranty coverage.

Master the load: There’s a rubbery ratio between towball download and claimed towing limit
Master the load: There’s a rubbery ratio between towball download and claimed towing limit

Most vehicle manufacturers quote a maximum permissible towball download in their specifications. In many cases it's a lot less than 10 per cent of their claimed maximum towing weight, so check.

If you exceed the manufacturer's stated maximum towball download, with or without a weight distribution hitch, you're giving them grounds to reject any warranty claim.

You can also alter the towball download by changing the payload distribution in your trailer or van but this needs to be done with care.

Moving payload to the rear to lessen towball download can cause the trailer to become unstable and create traction issues on your tow vehicle. Trailer payload should be carried as low as possible, and centred over the axle(s).

 

TOWING DECODED

FOR THE TOW VEHICLE

Kerb weight - Unladen vehicle, with a tank of fuel

Gross vehicle mass (GVM) - Kerb weight plus payload, including occupants and towball download

Payload - GVM minus kerb weight

Come to terms: The commonsense approach to the various limits is … don’t exceed them
Come to terms: The commonsense approach to the various limits is … don’t exceed them

FOR THE TRAILER

Aggregate trailer mass (ATM) - Maximum weight, including load, unhitched and sitting on the jockey wheel.

Gross trailer mass (GTM) - Maximum weight, including load but minus towball download, hitched to the tow vehicle.

FOR THE COMBINATION

Gross combined mass (GCM) - Maximum loaded weight of vehicle and trailer together.
Must always be less than GVM plus GTM.

 

MORE RULES YOU SHOULD KNOW

Brakes must be fitted to any trailer that weighs more than 750kg.

On a car licence, you can drive a vehicle with a GVM of up to 4500kg.

A dealer is breaking the law if he sells you a trailer that's too heavy for your vehicle to legally tow.

Van rules OK: Brakes, safety chains, no passengers …
Van rules OK: Brakes, safety chains, no passengers …

You cannot tow a trailer that's heavier than the maximum rated capacity of your towbar and coupling.

You cannot carry passengers in your trailer (including a caravan) while driving.

In some states, you may require more than one safety chain, if, say, your trailer weighs more than 2500kg.

 

HOW MUCH CAN THEY REALLY TOW?

Ford Ranger

XLT 3.2-litre

No title, From: Supplied
No title, From: Supplied

Manufacturer's claim: 3500kg

GCM minus GVM: 2800kg

Difference: -700kg

 

Toyota LandCruiser Prado GXL 2.8-litre

Manufacturer's claim: 3000kg

GCM minus GVM: 3000kg

Difference: Zero

 

VW Amarok TDi580 3.0-litre

2018 Volkswagen Amarok V6 - 3.5 tonne
2018 Volkswagen Amarok V6 - 3.5 tonne

Manufacturer's claim: 3500kg

GCM minus GVM: 2920kg

Difference: -580kg

 

Mitsubishi Triton GLS 2.4-litre

Manufacturer's claim: 3100kg

GCM minus GVM: 2985kg

Difference: -115kg

 

Jeep Grand Cherokee Limited 3.0-litre V6

Manufacturer's claim: 3500kg

CGM minus GVM: 3150kg

Difference: -350kg

 

Holden Colorado LTZ 2.8-litre

Manufacturer's claim: 3500kg

GCM minus GVM: 2850kg

Difference: -650kg

 

Toyota 200 Series LandCruiser GXL 4.5-litre

Manufacturer's claim: 3500kg

GCM minus GVM: 3500kg

Difference: Zero

 

Isuzu MU-X

LSU 3.0-litre

Generic towing shots for Bill McKinnon feature in
Generic towing shots for Bill McKinnon feature in

Manufacturer's claim: 3000kg

GCM minus GVM: 3000kg

Difference: Zero

 

Mercedes-Benz X350d 3.0-litre V6

Manufacturer's claim: 3500kg

GCM minus GVM: 2930kg

Difference: -570kg

 

Chevrolet Silverado

2500HD 6.6-litre V8

2017 Chevrolet Silverado 1500 High Country
2017 Chevrolet Silverado 1500 High Country

Manufacturer's claim: 5890kg

GCM minus GVM: 5310kg

Difference: -580kg

 

All vehicles are turbo diesel automatics. One-tonners are dual-cab 4WDs


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