Do you need airbag suspension?

Air spring suspension has been around for a long time; being available on luxury cars in the 1950s and on many trucks (and trains and aircraft, for that matter) since the 1940s.

'Airbags' are also increasingly fitted to caravans, camper trailers and motorhomes. But what’s all the fuss about, and is it worth having air suspension on a caravan?

What is air suspension?

Air suspension consists of a conventional suspension axle set-up -- either live axle or independent arms (usually the latter for caravans) -- with one major difference: air-filled conical reinforced rubber bellows instead of leaf, torsion bar or coil springs.

The air springs are matched to offer correct spring characteristics according to the weight of the caravan, and are usually supplemented by shock absorbers.

There are a few versions of air suspension; starting with the basic set-up that requires pumping up and deflating the airbags manually, using whatever means available (usually a portable air compressor). Inflation and deflation is enabled via a schrader valve (car tyre valve).

In better air suspension systems, the air springs are filled from an air reservoir tank fed by an on-board air compressor, that can be triggered manually (when stopped) to raise or lower the RV, either up or down or side to side.

The better units also have a pressure regulator that automatically triggers inflation of the air springs if they fall below their required pressure and/or set ride height.

How much?

Air suspension isn't cheap. It costs around $5000 for an air suspension kit, plus labour to fit to a caravan or camper.

For a retro-fit, it’s not a matter of just replacing the leaves or coils with the air bellows -- they need to have dedicated mounting points on the suspension arms or axle. Because air springs have a similar cylinder shape to coil springs, if you’re replacing coils you might find that the air springs fit up to the coil’s mounting plates nicely.

More often than not, you’ll need to have new mounting plates welded in. The air spring mounting points have to be carefully positioned, because if the location points are different the chassis may crack if not strengthened at the spring plate points chosen. A good installer should know all this.

While retrofitting is possible, it’s a lot easier to have air suspension integrated as part of a new caravan set-up -- there are many components to be added besides air springs and their mounting points, such as the air storage tank, air lines, air compressor and wiring. This may require the relocation of some components on your van, or result in less available storage space due to the extra equipment.

Air helper springs are not the same as air suspension. As the name suggests, they're fitted in addition to coil or leaf springs. However, this set-up is not really suitable for caravans, and usually reserved for vehicle rear suspension to level out ride when carrying heavy loads.

What are the advantages?

An air-spring suspension should provide a much improved ride compared to a leaf-spring or coil-spring suspension. You might ask why that's important for a caravan, given no-one is allowed in the caravan when it’s being towed.

In a perfect world, all caravans would be towed on silken-smooth freeways and could use any type of suspension, because there would be few bumps to absorb. But we all know that to get to some of Australia’s best destinations, caravanners can face some pretty bad, pothole-strewn and corrugated roads, both sealed and unsealed.

With air suspension there's less vibration and harshness on all the caravan components, including chassis, body and interior furniture, from the more supple ride. So less likelihood of long-term damage such as fatigue cracks or cabinetry coming loose, as well as less chance of stored items such as crockery being shaken about.

As well as the van and its contents, air suspension is also easier on suspension components and tyres. The tow vehicle also benefits -- we all know what it feels like in the tow vehicle when the van goes though a large pothole, even with an off-road coupling fitted. With air suspension, those road shocks transmitted though the coupling are cushioned.

A good air suspension set-up will also be height adjustable, so overall ride height and clearance can be increased on off-road tracks.

Air spring height adjustment also means you can set the ideal height when at camp, such as dropping overall height for an off-road van to make stepping up into the van easier.

You also shouldn't need  chocks under the wheels to level out the van anymore, because the air suspension can let out air on one side of the van so it sits level on sloping campsites.

The downsides of air suspension

As well as being costlier to buy and install, air suspension is more complex than steel suspension so there’s more to go wrong. It can also add weight to the van with the additional components required, so can eat into the van's payload.

While many caravanners will tow air-spring vans at the recommended travel height, if you increase the height (for better clearance off-road) with resulting higher pressure in the air springs, the spring rate does increase -- making for a firmer ride.

Air suspension also generally requires more maintenance than a conventional suspension (although a leaf-spring suspension does need an occasional grease). While good quality units are durable and long-lasting, the rubber bellows will perish eventually and start to leak.

There's also the risk if you tow off-road of air lines being severed by, for example, sticks being flung up. Poorly routed air lines can also chafe against the chassis or suspension components causing leakage.

The air compressor usually needs some periodic maintenance, such as cleaning the air filter.

Air suspension also needs a good charged-up house battery to function properly (assuming you’ve got an on-board compressor). Having let out the air on one or both sides of the van at camp, you’ll want to be able to pump up the springs before heading off again -- which won't happen if your house battery is flat or faulty.

Conclusion

Air suspension is a great alternative to conventional spring suspension if you plan to tow your van extensively on poor roads, smoothing out the ride and placing less stress on the van and its components.

However, you pay more for it upfront, and the additional components can take up more room, add weight and require some periodic maintenance.