Are you right on the ball?

The ball-loading of your caravan is one of the critical factors that determine its handling and stability characteristics and these can go awry if the weight on your tow ball is either too light, or too heavy.

That's the latest warning from the Caravan Council of Australia, which has even come up with a formula for predicting changes in ball-loading depending on how full (or empty) your caravan's water tanks are.

According to the CCA, the issue increases significantly if the mass of the tow-vehicle is not sufficiently high to be able to control any instability of the caravan, i.e. where the ‘tail wags the dog. In some countries like the UK, the trailer cannot weigh more than the tow vehicle, but there's no such requirement in Australia.

Most, but not all, caravan and chassis manufacturers test their different models to credibly determine the optimum minimum and maximum ball-loadings for safe handling performance.

I know some don’t, because I’ve had an empty new caravan behind me that was virtually untowable at more than 80km/h on a freeway.

However, in most cases, the reason for towing instability can be laid at the feet of the ‘tow-er’’ – you.

A major problem with many 'vans is that the mass-distribution - hence the crucial ball-loading - varies excessively, depending on the location and possible combinations of the (empty and full) contents of the water tanks.

In other words, your tandem-tank caravan should tow properly even if your rear tank is full and your front one is empty. Conversely, it’s your responsibility to know the limits of your tow vehicle and whether loading up the bed of your crew-cab ute, having an outboard motor on your A-frame and a full front water tank in your van is exceeding its permissible ball loading.

So you need to know the worst two combinations of the contents of your tanks, the effect on your ball weight and the maximum ball weight that your tow vehicle manufacturer allows.

You can safely assume that your ball loading will not vary much when similar-sized tanks on either side of the main axle (or tandem axle set) are both full. Most caravan systems draw from both tanks simultaneously, but on others you can manually select the tank (or tanks) to fill and which to empty first.

To complicate matters, some upmarket caravans reserve one tank for drinking water and another for non-potable water, such as you might use in a shower. In some off-road vans, you can fill this tank from a river when away from a town water supply, or bore and hence its level relative to your drinking water tank can vary considerably.

Finally, an increasing number of caravans designed for off-grid living, such as free-camping, are fitted with grey water tanks of up to 100 litres capacity. These tanks are usually fitted wherever there's space underneath your van, as few manufacturers ever envisaged their vans being towed any distance at speed with the ‘grey’ full.

It’s all pretty simple really, as most caravans with more than one tank have a tank level gauge inside and a default situation is to ensure that the water is balanced as close as possible on either side of the axle line, or at worst, the weight is biased towards the tow vehicle.

You can easily calculate the effect using the rule of thumb calculation based on the capacity of each tank and the reality that one litre of water weighs approximately one kilogram.

You should then be aware of the distance of each tank from the axle line, as the pendulum effect increases the further each tank is away from your caravan or trailer’s centre line. Think of the classic playground see-saw or scales that the green grocer and many people around the world still use to weigh things.

Quite simply, multiple water tanks should be positioned as close as possible to - and each side (front / rear) of - the axle(s). Think about this before you pressure your dealer to add additional tanks. The closer to the front of the van they are, the more weight is on your ball.

Finally, you should also know what weight your tow vehicle manufacturer allows on the ball – that is, the rear of their vehicle.

All vehicle makers work together with tow bar manufacturers to provide the maximum safe loading and they need to consider the ‘yo-yo’ effect, where the weight of your caravan’s nose rises and multiplies on bumps and corrugations.

Too much, too often and you may suffer chassis or tow bar mounting cracks.

This is why some caravans that tow perfectly well on smooth surfaces get unsettled when you crest a brow in the road, or on corrugations. What is happening is when the weight comes off the ball they become tail-heavy for a moment and become more susceptible to side winds and the vacuum effect of overtaking large vehicles.

This why I always give caravans and trailers with large rear bumper boxes, bike, boat or outboards racks, a wide berth when overtaking; their owners, really don’t know what might happen next!

Finally, you can’t solve all your problems by fitting a Weight Distribution Hitch (WDH).

While they can stop the tail of your tow car from sagging, this transfers its fulcrum point further forward, which on many utes approximates to a point of the chassis rear of the cab. And guess where they are prone to fracture?

So, do some homework before you hit the road, including reading some of the excellent technical articles on the Caravan Council's website.