Feature: Dispelling towing myths
We hear from the experts
"It's easy to think that your tow vehicle will behave in the same way with a load on the back, as it does without", says RACV's Chief Engineer Vehicles Michael Case, but experience soon shows us this isn't the case. So you start to talk to your friends, and search internet forums... and on it goes. With so many rumours out there you'd be excused for thinking that towing is a black art. But it isn't.
Caravan World with Motorhome World called on an army of experts to dispel (and in some cases to validate) the common myths held by drivers about towing.
MYTH: Using load levellers takes weight off the towbar.
Wrong. Whatever the weight imposed before load levellers are fitted is what is imposed after – you can't add more weight than the legal limit on a towbar just because you have load levellers.
MYTH: Tyres only need to be replaced when they have the minimum tread left.
Not quite. You need to also ensure they have not aged more than about six years as the rubber carcass deteriorates and can cause a dangerous blow-out. Cracks in the rubber is a certain giveaway that tyres have perished beyond safe levels.
– Philip Lord, Caravan World with Motorhome World magazine.
MYTH: It's easier to reverse a large trailer than a small one.
True. It's fairly common knowledge that a large trailer is easier to back than a small one. This is because the distance between the trailer wheels and the towball defines the radius of rotation of the trailer. A shorter radius defines a smaller circle. So, a given towball displacement will move around a greater percentage of the circumference of a small circle. This means that a shorter trailer will rotate a greater number of degrees for a given displacement of the towball.
– Paul Tuzson, extracted from Reversing a Trailer, originally published in Trailer Boat Magazine.
MYTH: When your trailer starts to sway, accelerating will correct it.
False. This is a very common myth. In fact, it’s one that my father taught me. The truth is, if you accelerate to straighten your rig when your trailer starts to sway, the reverse actually happens and you risk losing control.
– John Eggenhuizen, driving instructor, Tow-Ed.
MYTH: A pop-top caravan is cheaper to tow than a full height van.
Not necessarily. In preparation for my recent book The Australian RV and Caravanner's Guide we contacted about a dozen manufacturers to test this frequently-repeated assertion. We asked for the weights of vans that were the same lengths and fitted out identically, the only difference being full height or pop-top.
In all instances except one the pop-top was either fractionally heavier than the fixed-roof version or very close to equivalent. When pressed for the reason, manufacturers explained that the additional structural strength required around the open top of the pop-top cabin added some weight, and the roof itself weighs more on a pop-top than a fixed roof. So pop-tops do not always have a weight advantage.
If one was to travel a great distance into a stiff breeze it is possible that the pop-top would not require as much energy to pull through the wind as the full-height van, provided that the pop-top’s roof line is no higher than that of the towing vehicle.
MYTH: When towing over rough ground, tyres need to be at a higher pressure to protect them if they hit stones.
False. Comments like this are enough to start a lecture by Adam Plate if repeated in his presence. Adam and his wife run the Pink Roadhouse at Oodnadatta, at the end of a road littered with stones. The truth of the matter is that a tightly inflated tyre is just like a steel wheel. When it hits a rock or stone is does not conform or wrap itself to fit around the stone, but impacts the rock harshly. The result is that the tyre will sustain a star fracture and either blow out, or if on an alloy wheel it will deform the wheel.
It is better to drop a little pressure from the tyre, drop speed, and take care over rough ground. The softer tyre will act as a cushion and protect the van from road shock. By the way, low profile tyres on any sort of vehicle are inappropriate for travel over rough terrain.
MYTH: A big 4WD is needed to haul a big caravan.
Not necessarily. All vehicle manufacturers specify the maximum weight that may be towed by their vehicle. It turns out that in many instances there is a strong relationship between the size of the tow vehicle and the weight that it is legally permitted to haul. There are some surprises, though. I know of some people who have bought a 4WD only to discover that it did not have a large towing capacity. It’s the manufacturer’s figures (and the capacities of the towbar, towball, etc.,) that matter, not the vehicle size. We used to own an International 4WD ute that was no bigger than an F250: it had a towing capacity of around 6 tonnes, whereas the F250 is limited to 3.5 tonnes.
MYTH: The most economical gear for towing is fifth gear because the engine will be revving more slowly.
Not always. For those who can remember riding a pushbike fitted with gears, when you came to a hill would you select the highest gear to ride up the hill because that meant less pedalling? Of course not, because the amount of torque required to keep pedalling would have been much greater. And so it is with vehicles: the energy required for hauling in fifth or a tall gear may be greater than the energy required when towing in third or fourth gear. Forcing an engine to labour never saves fuel; it can also stress the gearbox. Running on a lighter load can return greater economy. Consult your vehicle’s owner handbook or dealer workshop manager for advice related to towing with your vehicle.
Of course, if you are pulling a light load, and the vehicle is managing easily, it will probably manage in fifth gear.
However, a lot depends on the design and construction of the gearbox. If fifth gear happens to be an overdrive gear, then there's a higher risk of gearbox damage even though the load may seem to be light. Some gearboxes are built with strong fifth gears, others are not. So, when all is said and done, you really need to check with the manufacturer's recommendations for the specific make and model. It will (almost) always be safer to tow when the chosen gear is 1:1 ratio rather than overdrive.
– Lloyd Junor, Aussie Outback Publishing and Caravan World with Motorhome World magazine.
MYTH: I have no problems with stability (despite my 350cc motorcycle on the rear). My long, three-tonne caravan always feels ultra-stable.
Think again. You are confusing stability and inertia (i.e., resistance to change). No rig with a heavy mass at its rear can ever be inherently stable. That rig can change rapidly from feeling ‘ultra-stable’ to going out of control, given a sufficient combination of upsetting conditions. These include (and especially) speed, cyclic side winds, road camber, etc.
MYTH: Heavy caravans do not need weight distributing hitches if the tow vehicle's rear springs are stiffened.
False. This shows a total and dangerous misunderstanding of basic mechanics. The effect of that weight on the car is the same as pushing down on the handles of a wheelbarrow: the front must lift. There is every argument for stiffening that rear suspension and fitting better dampers, but it makes no difference at all to the lifting effect. That WDH actually levers the front of the car down again.
MYTH: Setting rear brakes to lock up first will assist stability in emergencies.
Total myth. The brakes are at their most effective just prior to locking, but once locked, the friction between the tyre and road decreases rapidly. The trailer is far more likely to jack-knife.
– Collyn Rivers is the author and publisher of The Camper Trailer Book (and other publications on related topics).
His website is www.caravanandmotorhomebooks.com
MYTH: If it’s the posted speed limit it’s okay
For the past 10 years it has been legal to tow a trailer anywhere in Australia at the posted speed limit, except in WA, where the towing speed limit is 100km/h – the same as it is for trucks.
Does that mean it’s okay to haul a 2.5-tonne caravan at 110km/h (130km/h in some parts of the NT)? The short answer is: "No!"
A car or 4WD with a caravan bobbing along behind it is the most inherently unstable vehicle combination on the road, because the coupling point is behind the towing vehicle’s axle and, without the vehicle to hold it up, the caravan will fall on its nose.
Many vehicle makers put speed limitations on their cars and 4WDs when towing, in some cases reducing the maximum towing speed to the old legal limit of 80km/h. Read your handbook!
– Allan Whiting, technical editor, 4WD Australia magazine.
MYTH: It's not necessary to service your caravan or trailer.
False. It's very important to service both of your vehicles before you embark on a long trip. You need to make sure that the tyres on the towing and the towed vehicles are checked for tread depth, tyre condition and tyre pressure – and that includes the spare tyre.
The tyres and brakes are the two most important safety items on both of your vehicles, and in both instances need to be in tip top order to ensure a safe and trouble-free trip.
– Michael Case, RACV Chief Engineer Vehicles.