Stop the sway

COMMENT

I’ve got electric sway control on my caravan and trailer sway control on my tow car – or so I’m told – because I’ve never experienced them. And neither should you.

I know what sway feels like though: That white-knuckle feeling that your caravan might overtake you before you pass that slow moving vehicle; that lurch from a sudden side wind that requires two lanes to control, or that uneasy feeling when you feel the rear of your caravan being sucked towards an overtaking B-Double.

Most of my experience comes when reviewing new caravans that have been wrongly set up in the first place.

I recall one that developed dangerous sway above 80km/h on a freeway and the well-known (Campbellfield, Melbourne) manufacturer had the temerity to tell me it was because it was empty!

Their explanation was that the caravan had a light ball loading when empty, but this would rise to the accepted 8-12 per cent of tare weight range when the water tanks and the boot were full. Rubbish!

So what happens if you’ve been free-camping and your water tanks and gas bottles are empty?

I took another well-known caravan brand away for a trip north and it towed badly from the outset, to the point where my wife refused to travel further. My ‘fix’ was to fill the two 20-litre jerry cans on its A-frame and re-locate the spare wheel on its back bumper into the load bed of the crew cab ute I was towing with. It didn’t totally solve the problem, but my wife didn’t leave!

Basically, it shouldn’t happen if your caravan has been properly made in the first place, you haven’t tampered with its balance and you’ve loaded and hitched it up properly.

When I asked Trakmaster to build my current caravan, I specified the features I wanted to fit into its 15ft 6in x 7ft body, which included a separate shower and toilet bathroom.

But they wouldn’t agree to build it until they had discussed its dynamics internally, done calculations to work out to the millimetre where the tandem axle set needed to be located and worked out the empty and laden weight distribution to ensure it towed properly.

However, on my first trip, I thought they had got it wrong, as I sensed a slight nervousness around 100km/h.

I then wondered if the issue was with my Land-Rover Discovery 3 tow car and was perhaps a mis-match between its self-levelling air suspension and the similar Trakair system of the caravan. After all, Land-Rover specifically advises against fitting weight distribution hitches because of potential conflict, but I hadn’t.

So I started looking at simple things.

For one, my caravan was slightly nose down when hitched, so I figured that it was probably pivoting on the front tyres of its tandem set, rather than having all four tyres firmly planted.

Then I looked at my tow bar tongue. The original Land-Rover tongue extended about 30mm further rearwards in my after-marked Mitchell Brothers hitch than it would have in the original Land-Rover OEM yoke, effectively creating a lever effect.

So I searched through the range of Hayman-Reese tongues until I found one that went into the tow bar yoke right up to its flange and allowed the caravan to sit level.

At the same time I had Melbourne’s Harding Swift measure the ball loading at the optimum A-frame height to ensure that it sat within the desirable weight range. The caravan has a plated tare weight of 2432kg and the ball loading was 235kg, so I was happy.

Then I set the caravan’s tyre pressures even and those on the rear of the Disco slightly higher and, hey presto, it towed properly at all speeds, empty or laden, as its manufacturer had intended.

As a result, I have never needed to call upon its Dexter Sway Control or the tow vehicle’s Trailer Sway Control in nearly 30,00km of Outback travel – one third of that on unsealed surfaces. The devil was all in the detail!

So, before you blame your caravan manufacturer for your van’s instability, here’s a simple checklist:

1. Not all caravans have a heavy ball loading, specifically British and European vans, as being lightweight, they're usually towed by family cars or station wagons, rather than SUVs.

2. The important thing here is to maintain a similar ball loading whether empty or laden, so load your caravan carefully. Group heavy items (cartons of beer/wine/etc) as close to the axle line and as low as possible. Use overhead cupboards to store lighter bulkier things, like clothes, linen, towels, or voluminous consumables, like cereal boxes, toilet and paper rolls, etc.

3. If your caravan has twin water tanks, they'll most likely be located on each side of the axle line. Either fill, or half-fill both to a similar level and if you have a choice, drain the rear tank first.

4. Do not add weighty items to the rear bumper of your caravan. Even a 15-20kg bike and its rack can become a much heavier load on bumps, thanks to the lever action that this applies to the chassis.

5. You'll notice this on a bumpy road when the caravan rises and falls with the bumps. When the rear falls, weight comes off the ball, making the van’s tail heavy, less stable and more susceptible to side winds and hence, sway.

6. This means ‘no’ to after-market generator boxes or an extra spare wheel. At the very least, such items will place extra stress on your caravan’s chassis, potentially leading to failure later in its life.

7. Conversely, don’t add extra weight to the A-frame, like an outboard motor, generator box, etc. before checking with the manufacturer.

In most caravans, the point where the A-frame meets the main chassis rails of a caravan is the weakest point in its frame and unless designed for the extra weight and properly gusseted, it's where stress fractures can occur.

8. It sounds obvious, but make sure any heavy items can’t move around inside the van when you’re travelling. Apart from causing damage, they can upset its stability.

9. If your tow vehicle’s manufacturer allows you to fit a Weight Distribution Hitch, this can be a good idea on an SUV towing a caravan weighing over two tonnes.

SUVs generally have softer, independent rear suspension for more passenger comfort, but many tend to sag under the weight of a laden caravan. This can cause the caravan to tow ‘tail-up’ which makes it more susceptible to side winds and less stable to tow.

10. Properly fitted, a WDH will allow your rig to tow level again and restore some of the weight to its steering wheels, but beware. We have heard of instances of chassis cracking rear of the cabin where WDHs have been fitted to utes, which don’t have the roof or superstructure of their SUV brothers for support. We suggest you check with the manufacturer first before fitting one to any ute.

11. Finally, check your tyre pressures. On bitumen, you should travel with at least 40psi of pressure, measured cold, in your caravan tyres,– more in the tyres of single axle caravans than with tandems, where the load is shared.

Check with your caravan dealer for their recommendation.

As a general rule, I put around 5psi more pressure in the rear tyres of my tow vehicle, as these tyres are doing the most work, being hammered into the road every time your rig hits a bump.

If you have less pressure in your rear tyres, the rear of your tow vehicle – and hence your caravan – will be more prone to sway.

And I put about 5psi less in the front tyres to ensure better road grip, as they don’t have as much work to do.

Hot weather can change all this and if your pressures are too high, the tyres can potentially overheat, leading to failure.

But one size doesn’t fit all here. Get specific advice from your car and caravan manufacturer relevant to your rig.