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Pic: The Wanderer's first trip to Scotland in 1885, showing what can happen when a 2 tonne caravan goes off road.

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Gross Combined Mass Upgrades

by Collyn Rivers

PIc: courtesy caravancampingsales.com

PIc: courtesy caravancampingsales.com

In the past few months the general media has covered the import of changes in legislation relating to a federal ban on the ability to legally increase a tow vehicle’s towing capacity and/or the combined weight of a laden tow vehicle and trailer beyond its Gross Combined Mass. The ban affects only new registrations. It is not retrospective. That overlooked in some of the coverage is that a major part of the issue is historical inconsistencies between state and federal requirements.

For the better part of 100 years, caravan owners and caravan makers agreed that the laden tow vehicle needs to be about 20% heavier than the laden caravan, and that the caravan needs to be nose heavy by 7-10%. Europe by and large still follows this.

In Australia, in 1998 national towing rules for motor vehicle with a Gross Vehicle Mass (GVM) not exceeding 4.5 tonnes must not, without the approval of an authority, tow a trailer with a mass (including any load) exceeding the capacity of the towing apparatus fitted to the vehicle, or a relevant maximum trailer mass specified by the vehicle manufacturer.

In other words, you can tow the amount specified by the vehicle manufacturer or the capacity of the towbar (whichever is least).

There are two main issues: Gross Vehicle Mass (GVM) - a manufacturer rating that defines the maximum laden mass of the tow vehicle. It is generally possible to have that maximum increased prior to original registration. It is done by upgrading springs and shock absorbers etc. Uprating can also be done post-registration but is more complex.

The second issue relates to Gross Combination Mass (GCM). This too is a rating set by the vehicle manufacturer: i.e. the maximum permitted laden weight of a tow vehicle and trailer combination. For most combinations it is 5500-6000 kg. This shall not be exceeded.

The GCM is a major issue for owners of the most popular dual cab utes. Many are promoted as able to tow 3500 kg – yet as they typically weigh 2100-2250 kg unladen, there may be only 250-350 kg available if attempting to tow that 3500 kg. The trailer’s tow ball mass alone may take that rig to its GCM: i.e. no driver, let alone passengers, fuel etc. This has resulted in some owners grossly and illegally overloading their vehicle, or a 2500 kg (or less) tow vehicle legally (but unsafely) towing an up to 3500 kg caravan.

The most commonly quoted example is the 6000 kg GCM-rated Ford Ranger FX4 dual-cab ute. In basic form its tare mass is 2247 kg with 10 litres of fuel. Its nominal payload is 952 kg, but towing a caravan of its claimed 3500 kg results in it being 699 kg overweight. The available legal payload is a mere 253 kg. This is an actual example of the caravan’s tow ball loading alone likely to exceed the available payload. The rig is legal – but not usable as there is no available payload whatever for driver, passengers and fuel etc. There are several other utes in a similar situation.

Increasing the GCM

Until recently it had been possible (due to a less than clear Australian Design Rule), to increase the GCM, but there was no need to test or prove that the vehicle could operate safely at the now higher weight capacity. Prior to the June 4th ruling, a GCM increase potentially enables the tow vehicle to legally carry its original payload (or more) – resulting in it weighing 3500 kg and able to more safely tow 3500 kg. It was since realized that a flaw in the related Australian Design Rule, could also result in that Ford Ranger now towing a plus 4000 kg caravan.

In an assumed intent to clarify all this the Federal Government Department of Transport (June 2018) advised that:

‘The towing capacity of a light vehicle expressed as Gross Combination Mass (GCM) rating or Rated Towing Capacity or Maximum Braked Towing Mass rating must not exceed the value set by the first stage manufacturer. Second Stage Manufacturers are not permitted to increase the towing capacity as part of a Second Stage Manufacturer Approval that results in a GVM upgrade’.

This ruling is not retrospective. It applies only to vehicles modified under new or amended Federal approvals and then only applies to vehicles being modified prior to first registration under the Federal Government Scheme.

GCM upgrades are permitted on already registered vehicles under some state and territory regulations as long as they are individually vehicle inspected and certified as safe and fit for purpose by a registered engineer. The situation is, however, currently unclear in Queensland, South Australia, Tasmania and the Northern Territory.

The Federal Government Department of Transport (June 2018) clarification makes sense, but in RV Books opinion, only if (a) there is a legal procedure to ensure the tow vehicle be at least the weight of whatever towed, and ideally greater, not increase towing capacity. Further, there should be an option of a post-registration GCM upgrade to be made available in all states and jurisdictions.

This issue highlights Australia’s growing need for one uniform set of vehicle rules and regulations. This is not least because the rules of physics apply to all states and jurisdictions but right now Queensland seems more aware of the issues.

The content of this blog is equally true of conventional 4WDs, but many have a higher GCM than lighter dual cab utes.


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