Battle of the black boxes

The two combatants won’t openly admit as much, but it’s war out there in caravan sway control land and tongues rather than trailer tails are already wagging.

Al-Ko threw down the gauntlet in mid-2012 when it launched its Australian designed, developed and tested Electronic Stability Control (Al-Ko ESC) onto the market.

With the promise of taking the fear out of caravan towing for the legions of first timers and retirees, whose first experience is often as the captain of a tow car and trailer rig weighing up to five tonnes and more, it was welcomed with open EFTPOS by the market.

Manufacturers saw the opportunity to attract previously unsure buyers, predicting that it would also make towing more palatable to women and help sell the larger, heavier, increasingly better equipped and more expensive caravans they were producing.

As a result, Al-Ko ESC soon began appearing on the original equipment list of many more expensive caravans and today is offered either as standard or as an option costing around $1000-$1500 on the majority of full-height Australian vans and pop-tops.

Dealers saw another sales and bargaining point, helping them 'upsell' caravan size, while often tossing in ESC to clinch the deal, like other dealer-fitted options.

And insurance companies, sensing lower claim rates from inexperienced caravanners and sniffing a marketing edge, began offering discounted premiums.

CIL currently offers a 10 per cent reduction to customers whose vans are equipped with Al-Ko ESC, rather like car insurers offered reduced premiums to those who keep their cars garaged in safe post-code suburbs and offer cheaper cover to householders who fit security systems.

But now there’s another player in the stability control game, giant American axle, brake and trailer equipment manufacturer Dexter.

Although well established in Australia as a source of axles, suspension and brake systems to many caravan manufacturers, Dexter through their Australian and New Zealand distributors Melbourne Trailer & Caravan Supplies, immediately saw Al-Ko’s ESC as a market threat.

It wasn’t so much their stability control that was the issue, but Al-Ko’s insistence from the outset that their ESC could only work on its own electric brake systems. So we had caravan manufacturers, such as Victoria’s Goldstream, switch their supply from Dexter to Al-Ko products so that they could offer ESC, as customers were beginning to ask for it at the retail level.

However while Al-Ko were making ESC hay, Dexter in the United States were busy developing their own ‘Sway Control’ system – Dexter DSC – and rolled it out almost two years after Al-Ko launched on the Australian market, in late-2014.

While both systems are similar in retail cost, they’re fundamentally different in design and operation.

Here’s how they stack up:

Al-Ko ESC relies on sensors in its ‘black box’ mounted under the caravan to activate the unit when either one lateral movement of 0.4g force, or four in a row of at least 0.2g is detected, indicating that the caravan is swaying and the driver is in danger of losing control.

The unit then applies power progressively to both (or all four) of the caravan’s brakes until the sway is brought under control. Typically, the power for this ESC operation comes through an Anderson plug connecting the tow car to the caravan.

A key feature of the Al-Ko system is that it’s tailored to each size and weight of caravan and the power sent to the brakes is based on these pre-set values.

Dexter DSC in contrast is a ‘one size fits all’ system. While the caravan’s electric brakes draw the power for their operation from the tow car, the DSC ‘black box’ is powered by the caravan’s own battery (or batteries) and hence is independent of the tow vehicle. So in theory even if the caravan broke free of the tow car, the DSC sensors would apply its brakes.

DSC will also work on any serviceable and properly adjusted electric brake system, whereas Al-Ko from the outset insists that ESC only functions properly on its own electric brakes.

Caravancampingsales has heard whispers that under pressure from ESC fitters, this may soon be relaxed to allow the Al-Ko system to be fitted to Dexter-equipped vans.

DSC also detects sway differently.

Al-Ko’s ESC works off side-to-side movement, whereas Dexter DSC monitors circular movement, or what the Americans call yaw. This also allows it to detect vertical movement, such as when the wheels are passing over corrugations on an unmade road, whereas the Al-Ko system apparently doesn’t. 

When ESC detects a degree of predetermined ‘dangerous’ sway it sends the same power to all the caravan’s brakes, whereas the Dexter system only applies the brakes on one side to correct the sway, rather than brake the entire caravan. Thus DSC’s operation more closely resembles the stability controls fitted to most modern cars.

And whereas the maximum amount of brake force is pre-set in the Al-Ko system based on the caravan’s size, weight and even tyre size, the Dexter system will simply adjust to whatever brakes it has to work with, regardless of the caravan’s weight, its load and how well or badly that load is distributed.

This is reassuring on large caravans that often carry up to 300 litres of sloshing fresh, grey and even black water in several tanks and can have a payload of up to 1000kg – or none at all – under different towing circumstances.

This DSC is potentially retro-fittable to any caravan or trailer with properly functioning electric brakes.

So while you’re unlikely to lock wheels with the Al-Ko system, DSC will selectively send up to 100 per cent of power to the brakes on the appropriate side of the van to correct the sway, even to the point of wheel lock-up.

The other big difference between the systems is how they work off-road and this is the area that has led to Dexter being offered by a number of Australia’s best-known specialist off-road caravan manufacturers, including Queensland’s Bushtracker and Victoria’s Trakmaster.

The big problem when you get off smooth gravel or bitumen is what is called ‘nuisance’ braking. That is when the system cuts in unnecessarily when vertical wheel motion is interpreted as ‘sway’.

With the Al-Ko system, the solution is easy; when you get onto a corrugated unmade road, simply pull out the Anderson plug connector, disabling ESC.

With Dexter, the black box recognizes vertical movements and switches the system ‘off’ after five seconds of continuous disturbance until the road surface becomes calm again. Then, after up to five more seconds, it switches DSC ‘on’ again.

This ‘on-off’ status can be seen by the colour of the green or red light on the trailer’s A-frame, but unfortunately not by the driver. Melbourne Trailer & Caravan Supplies is discussing the option of a secondary dashboard light with their fitting agents as you read this.

So when you don’t want wheels locking up unnecessarily, the Dexter Sway Control is ‘off’.

Also handy for off-road vans, the DSC control box is ‘water resistant’ and according to Dexter, can withstand a good, albeit brief, dunking during a river crossing.

So which system is right for you?

Without exhaustive back-to-back testing on a caravan or trailer of similar size and weight under controlled circumstances, it’s impossible for us to make this call.

Both systems have been well tested, come from well-known and reliable manufacturers and are well supported in Australia.

Being on the market two years longer, there are more Al-Ko fitting and service agents currently on the ground, but Melbourne Trailer & Caravan Supplies has already trained 50 organisations to install and look after DSC.

If most of your travel is on the blacktop, then there are pros and cons for both systems, but one thing is certain: having something that stops caravan sway is an absolute life-saver and either of these systems is very cheap ‘insurance’.

If a lot of your time is spent off the bitumen, then it appears the Dexter DSC system offers specific advantages… for now.

One thing we can be pretty certain of though. Big insurance companies like CIL will almost certainly offer across-the-board premium discounts to caravanners, regardless of which system you fit. Just ask them.

Also just as certain, is that some time in the near future, State road transport authorities will mandate the fitting of some sort of stability device to all large caravans and the arrival of a second supplier only strengthens that likelihood. It’s very hard to mandate something when there is a sole supplier.

Finally, just like having an ensuite, or maybe a washing machine in your caravan, we see stability control being in demand on the used caravan market in the near future.

So if your van has ESC or DSC, it will simply find a new home quicker on Caravancampingsales!