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Legally compliant vans and trailers may not be dynamically safe.

There are many ‘lemon’ complaints against caravan and camper trailer makers and importers. Sure, some are dodgy, but even the conscientious ones don’t get much guidance in safe design from the current ADRs and Vehicle Standards Bulletins. Compliance with legal requirements doesn’t necessarily result in a safe combination of tow-vehicle and trailer.

The well-documented stability problems with fixed-drawbar trailers – caravans, camper trailers and boat trailers included – is caused largely by the fact that they’re inherently unstable. Without frontal support all these trailers drop their noses into the dirt.

In the trucking world, a fixed-drawbar trailer with a non-steering, close-coupled group of two or three axles is called a ‘pig’. There’s a reason for that.

First up, let’s get some of the confusing nomenclature out of the way. A trailer with axles at the front and rear is a full-trailer. A trailer with axle or axles predominantly towards its rear end is a semi-trailer. In other words it’s a ‘half-trailer’, because it relies on a tow-vehicle coupling to support its front end. In contrast, a full-trailer is stable without a tow-vehicle being attached.

In modern parlance, mention ‘semi-trailer’ and everyone thinks of a heavy vehicle combination, but, technically, any trailer that needs its tow vehicle for support is a semi-trailer. A fifth-wheeler is a semi-trailer and is called a fifth-wheeler, because, back when the semi-trailer was first developed the early 20th Century, trucks had only four wheels, so the round, turntable coupling became known as a ‘fifth’ wheel.

Let’s have a look at the trucking world, briefly, because working trucks and trailers have developed around the need for function before form. Trailers that work with heavy payloads need to be stable.

Trucks that tow trailers

By far the most common type of articulated heavy truck combination around the world is the prime mover (‘tractor’ in Europe and the USA) coupled to a semi-trailer. The fifth wheel coupling is above, or slightly ahead of, the rear axle(s). The next most popular is a truck pulling a full-trailer, known in Australia as a ‘rigid and dog’ combination. The trailer has a steerable front axle(s) arrangement, using a sub-frame and turntable.

There are a relatively small number of ‘rigid and pig’ combinations around the world, in which the trailer axle or axles are grouped near the centre of the trailer and do not steer. The coupling is an oversized towball on a bar, or a pin coupling.

Pig trailers are easier to reverse than dog trailers, because they have only one articulation point – the coupling to the truck – where a dog trailer combination has an articulation point at the drawbar coupling and another at the steerable front axle. Backing up a dog trailer needs practice!

Pig trailers are used in Europe for mainly light loads behind medium-sized trucks. In Australia, two-axle pigs are sometimes used as tippers behind rigid trucks.

A third type of heavy trailer is the tag trailer that looks like a pig trailer, but has its axle group towards the rear of the trailer, like a heavy semi-trailer. These are usually used for machinery transport, connected to a rigid truck.

In the trucking world the two principal vehicle types are a semi-trailer combination, where the half-trailer sits on a coupling that’s mounted within the prime mover’s wheelbase and a rigid truck pulling a full-trailer. 

In the case of a semi-trailer combination the fifth wheel coupling transmits around half the trailer axle’s gross mass figure to the prime mover – mainly to the drive axle(s).

In the case of a rigid and dog combination the drawbar coupling contributes virtually no weight to the truck at all, because the trailer is inherently stable.

So, if we draw any lessons from the trucking world of successful articulated vehicle combinations we’d opt for the proved stability of a fifth-wheeler or a vehicle pulling a full-trailer (dog trailer).

The recreational trailer

Caravans, camper trailers and boat trailers are semi-trailers that rely on a tow-vehicle coupling for stability. The attraction of a drawbar-trailer with fixed axle(s) is that it’s easy to couple to the towbar of virtually any standard vehicle. Also, because there’s only a single articulation point, it’s relatively easy to reverse and manoeuvre.

However the real-world situation isn’t that simple and so we’ve covered the vexed issue of ball weight and trailer stability elsewhere on the OTA website.

A fifth-wheeler puts much more coupling weight on its tow-vehicle than does a drawbar-trailer, but that weight is above the rear axle, not a metre or more behind it. Like a semi-trailer truck combination it’s inherently more stable than a towball-drawn trailer and is as easy to manoeuvre.

The drawback of a fifth-wheeler is that it needs a ute or truck to tow it and many people want to use a wagon.

What about a tow-vehicle pulling a recreational full-trailer? This combination would have great inherent stability, thanks to wheels at all four corners; all weight within the wheelbase and no unbalancing front or rear overhangs; no ball weight to destabilise the tow vehicle and no need for weight distribution bars, jockey wheel or stands.

We’ve seen some full-trailer caravans in Europe, but they’re scarce.

The sole apparent reason for this virtual absence from the market is the difficulty of reversing and manoeuvring a full-trailer, because of its two articulation points. And as any rigid and dog truck driver knows, the shorter the drawbar, the tougher the reversing job.

There is a way of making the full-trailer more manoeuvrable and we’re working on a design with some engineer mates. Watch this space!

In the meantime, let’s look at where the current designs of caravans, camper trailers and boat trailers are lacking.

Instability built in

There’s enough flak in the caravan and camper trailer world about ‘lemons’, so we don’t need to go into the type of issues that buyers often have. Suffice to say that it’s much easier to set up a small-volume trailer business than to make 4WDs from scratch and this relative ease lets dodgy makers in.

Also, even with then best will in the world and in full compliance with Australian Design Rules (ADRs) and the guidelines provided by the relevant Vehicle Standards Bulletin (VSB1), a caravan or camper trailer maker can produce a vehicle that’s not within the spirit of these rules.

Government perception seems to be that trailer design and construction doesn’t need the same degree of regulation or scrutiny that passenger vehicle, 4WD or truck makers must comply with.

Here are the applicable ADRs for TA (non-braked) and TB (braked) trailers up to 3.5 tonnes GVM:

23/02 – Passenger car tyres – TA and TB

38/05 – Trailer braking systems – TB

42/05 – General safety requirements

43/04 – Vehicle configuration and dimensions

44/02 – Specific purpose vehicles

61/02 – Vehicle markings

62/02 – Mechanical connections between vehicles

92/00 – External projections

95/00 – Installation of tyres

The list looks pretty comprehensive, doesn’t it? However, there’s no design requirement for static and dynamic stability testing at different loads, the positioning of liquid tanks or weight transfer to the tow-vehicle’s coupling. 

In fairness to lawmakers and trailer makers, the recreational trailer scene is diverse and so are the likely towing vehicles. In all respects, truck-trailer makers have a much easier job, because a heavy trailer designer is guided to a very large extent by legal axle weights and dimensions. Also, the trailer must ‘fit’ behind a known type of tow-vehicle and be compatible with its electrical and braking systems.

More recently, trailer electronics must integrate with the tow-vehicle’s ABS/EBD/ESC system and all truck makers have broadly similar connectivity.

Electronic stability control on trucks and trailers is mandated in most global markets, as is autonomous emergency braking on both truck and trailer.

Recreational trailer makers have no such strict guidelines to work within, because the eventual customers’ tow vehicles are unknown.

ADRs don’t do the job with trailer design

ADRs were originally developed for compliance by major automotive manufacturers, who have extensive design and testing facilities. There’s no ADR, for example, that covers the need for a vehicle to handle safely or not leak when it rains, because governments know that vehicle makers must do that if they are to succeed in competitive markets.

If you visit vehicle makers’ R&D facilities you’ll see various test booths where components and whole vehicles are undergoing stress and ‘shaker’ durability and water, ice and heat soaking. Test tracks extend that testing to all types of road and track conditions.

Most Australian recreational trailer makers and importers have no industry-standard static and dynamic testing regime for their finished products, although many do at least some real-world evaluation. Certainly, there is manufacturer testing of all ADR-covered items that are incorporated in the trailer, but the finished trailer does not have to comply with any behavioural standards.

We think it’s in the interests of everyone’s safety that every trailer model should be proved to brake and corner safely, when loaded to its plated maximum, with its loaded ball weight, behind a typical tow vehicle for that class of trailer. 

We know, from our own many years of real-world testing, that there isn’t a standard 4WD wagon in the market that can safely tow a 3500kg trailer that has 350kg ball weight. At a minimum, it will need heavier-capacity rear suspension and heavy-duty weight distribution bars, but may still exceed the vehicle maker’s rated rear axle capacity.

Even a 4WD ute is at or above its axle weight limits with such a trailer in tow, except for the North American brands that are purpose-designed to tow heavy trailers.

Unfortunately for tow-vehicle buyers the vehicle maker fits an accessory towbar and electrical plug, and stipulates in the owner’s manual what the vehicle’s permitted GVM and axle weights are. That’s the end of the vehicle makers interest in the future towing task.

The recreational trailer maker plates the caravan, camper trailer or boat trailer with the minimal information required by law that, incidentally, doesn’t have to include the tare and maximum permitted loaded ball weight figures. That’s the extent of the dealer’s interest in what vehicle is towing it.

Try getting your money back from a trailer dealer when you discover that the plated tare weight is wildly optimistic and the loaded ball weight exceeds the capacity of your tow vehicle!

It gets worse. Heavy truck ADRs regulate the design of braking systems and both truck and trailer makers must comply. Braking balance is inbuilt at the truck factory and the trailer factory and no-one can alter any component of that ADR-approved braking system without suitable qualifications. In contrast, the recreational trailer section of ADR 38/05 stipulates a trailer braking system with an in-vehicle brake-balance controller.

ADR38/05 allows a tow-vehicle driver to vary the timing and intensity of his recreational trailer brakes, without the need for any training, instruction, experience or licensing. That’s sheer insanity.

Vehicle Standards Bulletin

But there’s more. VSB1 requires the load area of a recreational trailer to be equidistant forward and aft of the axle(s), but there’s no compliance formula for centre of gravity lateral or vertical positioning. 

We’ve seen a new caravan, whose manufacturer assured us complied with all ADR and VSB1 requirements, fitted with a drop-down load platform on the rear, to carry a quad bike. It also featured a front-mounted winch and fairlead arrangement, allowing a 3.5-metre-long ‘tinny’ to be hoisted onto its roof. It may have been compliant, but we doubt it met the spirit of VSB1.

Most Australian-designed caravans and camper trailers have large front-mounted bins, for stowing anything the buyer can fit in. Typically, they’re loaded with heavy kit and that’s not desirable in a ‘pig’ type trailer, where everything heavy should be mounted as close to the axle(s) as possible. 

(European caravans don’t have large frontal bins, because ball weight is regulated to a maximum 110kg. If your tow-vehicle and trailer get roadside-weighed and you have more than that figure, you’re fined and grounded.)

In the case of forward-fold camper trailers, all but one of these we’ve weighed had very high loaded ball weights, because designers know that the forward-fold/dinette layout works best with the axle set as far aft as possible. Once again, these designs may be ADR and VSB1 complaint, but they impose a disproportionate amount of weight onto the tow vehicle.

Clearly, there’s need for an additional recreational trailer design ‘tool’, to help relatively small-volume makers develop or import designs that are as stable as possible.

As we have seen, the current recreational trailer is a semi-trailer design, which is inherently unstable: without support it falls on its ‘nose’. That’s the worst type of vehicle to be produced by relatively underfunded makers.

Also, as many trailer buyers have found to their cost, it’s often difficult to prove that trailers they’ve bought aren’t ‘fit for purpose’ under Australian Consumer Law, because the manufacturer can show it has complied with ADRs and VSB1. This situation reinforces our point that there’s more certification of trailers needed.

The ACCC is something of a toothless tiger, so although it has been made aware of many caravan owners’ complaints, nothing has happened. Every time we ask the ACCC if it’s doing anything on trailer design or compliance issues were told: “The ACCC makes no comment on its investigations”. Great.

European vs Australian compliance 

In Europe, there’s recognition of the limited resources of small-volume trailer makers, but the process is more rigorous than it is in Australia, where self-certification is allowed. Self-certification has never worked in any industry and is simply a way for governments to abdicate responsibility.

In theory, self-certification is backed up with physical audits, but the process isn’t well organised and manufacturers have warning of inspection dates.

The Commonwealth Government is developing new Road Vehicle Standards legislation, but to ensure that governments, manufacturers and importers have sufficient time to prepare for the transition to the new arrangements, implementation was  delayed from the proposed introduction date of December 10, 2019.

The Government said it would continue to work with all affected stakeholders to agree on and set a new commencement date, which was promised to be no later than 1 July 2021.

Hopefully, the new RVS law resembles the EEC model that would eradicate the worst of Australia’s shonky caravan makers.

In the EEC, trailer makers have the choice of two compliance routes to achieving an EC Certificate of Conformity (EC – CoC), proving that the vehicle meets with European Communities Whole Vehicle Type Approval (EC – WVTA)

Most trailers are type-approved to European Community Whole Vehicle Type Approval (EC – WVTA) standards. ‘Type approval’ involves an assessment of certain aspects of the trailer design, inspection of a prototype and assessment of the production facility. This must all take place before production of the trailers starts.

Alternatively, specialised trailers built in low numbers can be assessed individually after they have been built. This is done by the Vehicle Operator Services Agency (VOSA), under an Individual Vehicle Approval (IVA) inspection. In this scenario every single trailer produced must be towed to a VOSA test station and inspected. 

From our research, the VOSA process seems to be more thorough than the rather ad hoc Australian trailer inspection norm.

If you want check the safety and legality of your towing combination, check out our calculator.





























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