Top tow tugs too light?

To safely tow a caravan weighing 3500kg you really need a loaded tow vehicle weighing no less than 4550kg.

That’s one of many controversial recommendations made by the Caravan Council of Australia (CCA), an independent body trying to raise RV manufacturing standards in Australia and protect caravan buyers from shoddy practices.

According to a comprehensive tow vehicle buyer’s guide published on the

Council’s website, the loaded weight of the tow vehicle should be at least 1.3 times the mass of the loaded trailer or caravan.

The ‘1.3 rule’ would eliminate most of the

increasing number of locally sold dual-cab utes and 4WD wagons with 3.5 tonne tow ratings from really heavyweight towing duties, even the popular Toyota LandCruiser 200 Series. 

In GXL diesel form the ‘Cruiser has a Gross Vehicle Mass (GVM) of 3350kg, which according to the formula would mean a maximum 2600kg van.

CCA founder Colin Young, an automotive engineer and former employee of the now defunct Recreational Vehicle Manufacturers Association of Australia (RVMAA), said the radical recommendation is based on decades of towing experience as well as ‘controlled’ trailer testing he witnessed around 40 years ago in the US conducted by a major automotive manufacturer.

Held under “optimum conditions”, the testing involved ‘moose avoidance’ or lane changing manoeuvres, as well as computer simulations, to determine optimum trailer and tow vehicle combinations for safe driving.

“(If set up properly) it was quite possible to tow (the trailers loaded with race cars), not that you would do it, at 100mph (161km/h) and do moderate swerves,” he said.

“You’d get into major trouble at just 40mph (64km/h) if you had a trailer that wasn’t set up correctly, or if the tow vehicle was not heavy enough or not suitable for pulling it.”

As well as sufficient mass to prevent the ‘tail wagging the dog’, the CCA also suggests a minimum amount of grunt from the tow vehicle’s, preferably turbo-diesel, engine.

For power, the ratio should be at least 25 for kW to GCM (tonne), and for torque, more than 65 for the ratio of Nm to GCM (tonne).

So in the case of a tow vehicle with a Gross Combined Mass (GCM) of six tonnes, it should have at least 150kW and 390Nm.

“It’s based on the acceleration rate (which) allows for a reasonable distance through overtaking at different speeds…” he said.

“And this is where a lot of people come unstuck… they’re not used to the extra mass and wind resistance that it takes to accelerate (when towing). You can’t have too much power or torque.”

Also crucial according to the CCA is tow bar overhang, as measured from the centre of the rear axle to the centre of the towball. It should be no more than 30 per cent of the tow vehicle’s wheelbase.

 “Some (dual cab utes) would be up to 40 per cent or even 50, and that makes a big difference (to handling),” Young says.

The best option for a dual cab ute is a fifth-wheel caravan where the “articulation point” is more ideally located above the rear axle.

However, Young admits these are only suggestions and that the most important consideration is that "the combination is 100 percent legal (compliant), regarding masses and ratings, and provides the best possible safety on the road”.

“It may not be possible to find a tow vehicle that meets these figures, but it would be most prudent to select a tow vehicle that comes close to meeting them,” he says.

While shying away from recommending specific tow vehicles, Young does point to the larger, more powerful imported pick-ups with their much higher towing capacities as preferred options for three tonne-plus towing.

“I don’t really get involved with individual tow vehicles or their specifications. But if you need a (Ford) F-250 or a Dodge Ram or something like that for safety, so be it.”

American trucks also get a ‘tick’ for their longer wheelbases that help provide “more stability on straight roads, and cause less axle load variations because of the coupling force on the tow-bar”.

“Basically, you can’t have too much mass as a tow vehicle and you can’t have too much power to get out of trouble,” he says.

“(The tow vehicle) might be legally safe but is it physically safe or reputable for towing such a (heavy trailer)?”