RV Construction Legislation

The front cover of VSB 1

The front cover of VSB 1


The National Code of Practice for constructing small trailers in Australia is set out in the Federal Government's Vehicle Standards Bulletin Number 1, otherwise known as VSB1. You can read VSB 1 here.

VSB 1 has served the trailer industry well for many years and sets important quality and other standards that all small trailer manufacturers must follow.

RV Books would like to see a few small but significant changes to VSB 1 to help make these rules clearer and safer for everyone.


VSB 1 applies to 'road trailers – including new trailers or used imported trailers – with an aggregate trailer mass (ATM) of 4.5 tonnes (4,500kg) or less'.

RV Books would like to see the scope of VSB 1 align precisely with the 'light trailer' definitions used in state and territory trailer towing legislation. It is not helpful having references to 'road trailers' in one document (VSB 1) and 'light trailers' in others (state and territory legislation). In turn, states and territories should agree a single light trailer definition and weight benchmark - see here how they are currently defined.

As mentioned in our blog titled 'Mixed Messages', the easily understood term ‘maximum trailer mass’ ('MTM') should be used instead of the antiquated and poorly understood 'ATM'.

Trailer Plates

VSB 1 states: 'The vehicle plate must show at least the following information:

  • Manufacturer's or Importer’s Name (whichever party takes responsibility for the certification statement);
  • Trailer Model;
  • Vehicle Identification Number (specified in Section 4);
  • Date of Manufacture (month/year, e.g. 02/08);
  • Aggregate Trailer Mass (kg); and
  • The Certification Statement (specified below).'

RV Books would like to see Tare Mass added to this list (as required by the CIAA) as well as a 'Maximum Payload' figure (see below). The definition of ATM should either be simplified (see below) or replaced by 'MTM' (see above).

RV Books would also like to see a Maximum Recommended Speed Limit for the trailer, set by the manufacturer (not as part of tyre speed limit information, which is confusing) and included on the compliance plate.

ATM Definition

VSB 1 defines ATM as 'the total mass of the trailer when carrying the maximum load recommended by the manufacturer. This includes mass imposed onto the towing vehicle when the combination vehicle is resting on a horizontal supporting plane.'

Firstly, this definition mixes an actual weight ('the total mass of the trailer') with a maximum weight allowance ('maximum load').  We believe a weight benchmark should either be a maximum allowance or an actual weight, not a mixture of both. Consumers become confused.

Secondly, we wonder how many consumers realise that in order to 'include mass imposed onto the towing vehicle', the trailer must be weighed on a weighbridge whilst disconnected from that vehicle?

Thirdly, whilst this definition might make sense from an engineering point of view, it is not practical for the consumer, who will not unreasonably ask where they can find written the 'maximum load recommended by the manufacturer' (nowhere to our knowledge, but see 'Payload' below).

RV Books would prefer to see the ATM definition simplified to 'the maximum laden weight of the trailer when disconnected from a tow vehicle' or, better still, this same definition applied to the new term 'Maximum Trailer Mass'.


Payload is not discussed in VSB1. Payload relates to the weight of personal effects added to the trailer by its owner. Exceeding payload is dangerous but is commonly found in road safety checks carried out by police in conjunction with caravan clubs and other organisations.

Maximum Payload is a new term that we would like to see introduced for trailers and set by manufacturers. It is the maximum weight of personal effects that may be added to a trailer. Minimum Payload is a minimum payload allowance that could be stipulated in VSB 1 and built into new trailers. Motor homes currently have (nominal) Minimum Payloads but trailers do not.

RV Books would like to see a Minimum Payload stipulated for the construction of new trailers in VSB 1 and a Maximum Payload figure included on the trailer compliance plate.

Minimum Payloads for trailers should be based on the number of axles a trailer has and should be set at a high enough level to take into account the weight of water, gas and personal effects but not so high as to become dangerous. It is desirable because some trailers are so heavily constructed and/or have so many appliances that their effective payload is very low. It should encourage moves towards lighter trailer construction.

Maximum Payload stated on the compliance plate would remove the need for consumers to do calculations of their own (i.e. deduct Tare Mass from ATM) in order to calculate their maximum payload. It also removes the confusion over what items are/are not included in Tare Mass.

Maximum Payload would need to be qualified by two statements. Firstly that Maximum Payload includes the weight of water and gas and is determined at the time of trailer manufacture (since payload may change over time as successive owners add their own accessories). Second, that Maximum Payload is calculated on the assumption that payload is correctly distributed throughout the trailer.

Dealers should be required to weigh each used trailer they sell and advise buyers in writing of any changes to the trailer's maximum payload since it was manufactured as a result of additions/changes by previous owners. 


Gross Trailer Mass ('GTM') is defined in VSB 1 as 'the mass transmitted to the ground by the tyres of the trailer when coupled to a towing vehicle and carrying the maximum load recommended by the manufacturer or importer, approximately uniformly distributed over the load bearing area'.

RV Books believes that the GTM calculation is relevant primarily to semi-trailers and that only ATM (or MTM) is needed in 'pig' trailer construction. Consumers might become confused if they have multiple maximum trailer weights to comply with. 


Number Plates - VSB 1 references to number plates should be modified to take into account the 'arc of visibility' rules required in some states to allow the plates to be easily read by road cameras.

Tyre Placards - Weight benchmarks for tyre placards ('trailers with a GTM not exceeding 3.5 tonnes) should be the same as the definition of VSB 1's scope (i.e. 4.5 tonnes ATM).

Safety Chains. VSB 1 should explain clearly how they are to be used (e.g. crossed if there are two, long enough to permit turning and the application of breakaway brakes but short enough to prevent the A-frame from hitting the ground if the coupling becomes disconnected). These guidelines should then be reflected identically in all state and territory legislation.

Weight Distribution Hitches. VSB 1 should actively discourage their use - they solve one issue but introduce new ones.

Battery Monitoring Devices. VSB 1 should form a view on whether a battery monitoring device must be installed in the tow vehicle to warn a driver that the trailer's battery charge is too low to permit activation of breakaway brakes (currently a requirement in NSW only). These rules should then apply nationally.

Smoke Detectors should be made compulsory.

230 volt Electrical Installations in trailers should be carried out only by a qualified electrician in all Australian states and territories. Currently this is not a requirement in Victoria.

Tell us whether you think these changes are reasonable.

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