08/04/2024
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Motorhome air suspension: all you need to know

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Motorhomes are heavy beasts and the additional weight of equipment and height of the bodywork can increase the loads on the suspension

Manufacturers allow for the extra loads with the chassis and suspension systems they specify, but it’s possible to make significant improvements over the standard set-up.

As well as improving ride comfort, uprated springs or air suspension can significantly improve handling and safety, as well as other added benefits.

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An introduction to motorhome suspension

At its simplest, a suspension system is designed to isolate the passengers and cargo from the harshness of road surfaces.

Leaf springs were once the most common suspensions system; today, such systems are still used on the rear axle of the most common motorhome base vehicles. Leaf springs are basic but are robust and functional.

MacPherson struts are usually found on front axles. This is where a strut utilising a coil spring with integral shock absorber provides independent wheel suspension.

While it can be said the main components of a suspension system are the leaf or coil springs, modern sophisticated suspension systems also rely on an associated shock absorber and linkage systems such as anti-roll bars to provide maximum ride and handling comfort.

Campervans based on the likes of the VW Transporter will have coil spring systems on all four wheels. Motorhomes with an Al-Ko chassis will have Al-Ko’s torsion bar suspension on the rear axle; the wheel hub is attached to a swing arm and a torsion bar extending through the rear axle tube. As a rear wheel moves up or down the swing arm meets resistance to movement from the twisting of the torsion bar in the same way a coil or leaf spring flexes.

All these systems have their benefits and drawbacks, but one thing manufacturers of air suspension argue is all the existing suspension systems can benefit from replacement by air suspension.


What is air suspension?

Air-filled bags that link to a powerful compressor and can be adjusted to keep the vehicle level and stable. It’s tried and trusted technology that is widely available on motorhomes.

Air suspension allows the motorhome to carry a heavier load (ideal if you are up-plating for greater payload). It can also level the motorhome and allow the driver to adjust the pressure to give optimum ride comfort and on-road stability.


How does it work?

Air springs are tough rubber bags or bellows inflated to a pressure and height to provide suspension. By adding an air compressor, height sensors and electronic controls, full air suspension systems can instantly control the quality of the ride and handling to different load situations.

It’s important when considering systems to appreciate what’s actually on offer. Auxiliary or supplementary air suspension is a far cry from full air suspension. Full air systems replace existing suspension springs, while supplementary systems work with the existing suspension.

A full air system offers a multitude of side benefits and a greatly improved ride experience, while the supplementary system – known as air assistance – has a more limited offering, as does full air suspension on just one axle. But, don’t dismiss air assistance, as it still offers considerable ride improvements at a much lower cost than full systems.


How much does it cost?

Basic manual air assistance kits cost from around £250, with full air suspension and/or levelling systems rising to around £10k.


How long does it take to install?

Basic air-assistors – such as air bags that replace the rear axle spring assistor – are relatively simple to fit and can be tackled by experienced home mechanics. It might take you a bit longer than the couple of hours an experienced professional would need.

However, to fit uprated front springs, you’ll need a hefty spring compressor, which most home mechanics will not have access to. And, levelling systems and suspension upgrades that involve replacing the whole spring assembly are also best left to the professionals. Expect the time for the installation to be between one and two days, depending on the complexity of the system.

Certain systems also need to be linked into the braking system so we advise that all the systems detailed here are fitted by professionals.


Types of air suspension

Semi-air suspension

A Goldschmitt Zusatzluftfederung rear semi-air suspension

(Photo courtesy of Goldschmitt)

Air assistance or supplementary air suspension systems are easy to fit as they work alongside the existing leaf spring suspension on the rear axle. A basic kit can cost as little as £350 excluding fitting and you will find many suppliers of kits and installers. Typical of these is Marcle Leisure, which specialises in the supply (no fitting) of a range of kits and spares.

A common reason for fitting air assistance is due to onerous loadings imposed on a chassis by a motorhome. Standard commercial vehicles will, at times, be fully loaded to their designed maximum gross weight (GVW) and, equally, they will spend time empty or partially empty.

A common reason for fitting air assistance is due to onerous loadings imposed on a chassis by a motorhome. Standard commercial vehicles will, at times, be fully loaded to their designed maximum gross weight (GVW) and, equally, they will spend time empty or partially empty.

Motorhomes, though, are always close to being fully loaded on and off the road. As soon as the motorhome converter starts fitting the interior, including fridges and cookers, the springs will start to move down. The majority of motorhomes will be at or very near GVW, if not overloaded.

Original leaf spring suspension starts life well enough, but several years on, the suspension becomes tired – sometimes in overloaded situations, symptoms of flattened springs appear in as little as six months. Once springs have become tired, there is less travel and therefore much less ability to absorb shocks from the road. VB Air Supension has this really simple online diagnosis tool.

It should be noted that, where the condition of the springs is exacerbated by overloading, the weight issue has to be addressed – either reduce the weight or get the motorhome uprated. The addition of air assistance will resolve the flattened springs and reintroduce some welcome suspension travel back into the vehicle.

What it won’t do is make an overloaded axle legal. There is a formal procedure for uprating a vehicle and it is best to consult a specialist like SvTech for advice.

Air assistance doesn’t allow any great variation in level due to the constraints of the existing suspension springs, but it will eliminate rear end droop. With a dual-chamber system, the separate air lines provide independent pressures and permit a degree of compensation for uneven loading and transverse sagging.

Additional add-ons to a basic kit include pressure gauges for instant checking and an on-board compressor for convenient pressure top-ups so you don’t need to use a forecourt air line. An advantage of basic kits is the small impact on the vehicle’s payload allowance, adding as little as 8-10kg.

Pros and cons of semi-air/assistance kits for motorhomes

Pros

  • Improved cornering stability and reduced body roll
  • Increased ground clearance for ferry ramps and steep driveways
  • Reduced uneven wear by maintaining transverse ride height
  • On-site levelling and benefits for draining waste tanks and showers
  • Smoother ride over bumps and uneven surfaces

Cons

  • Cannot be used to combat overloading problems
  • Doesn’t allow for a large variation in level

Full air suspension

A VB full air suspension

(Photo courtesy of Rob and Sandy)

Suspension design is based on achieving the most suitable trade-off between comfort for passengers and the need to achieve good traction and accommodate load variations and the amount of axle travel. In such a complex situation, it’s little wonder some compromises are inevitable with standard commercial vehicle chassis where value for money is always key.

Hence the scope for full air suspension to improve the ride comfort and handling, but the cost of an automatic full air suspension system including fitting is likely to be in the region of £5,000 to £8,000 depending on the manufacturer and sophistication of controls.

Because of regular air pressure changes, automatic systems require an air pressure vessel to supply the quantity of air needed. The pressure vessel must include a drying system for incoming air to prevent a build-up of moisture in the bellows that can cause problems in freezing conditions.

Goldschmitt’s ADC full vehicle air suspension even offers a vehicle weigh facility, though all this sophistication not only adds to cost but weight. A full four-corner air suspension system on a standard Fiat Ducato chassis is likely to weigh up to 60kg, depending on what kind of leaf springs are removed. So, watch your payload.

A huge advantage of full four-corner motorhome air suspension systems, in addition to improvements in road holding and comfort, is the ability to vary levels significantly when static. Front seat passenger and driver are also said to receive greater levels of comfort, because for the likes of a Fiat Ducato, the front seats are almost directly located over the suspension system.

Fitting full air suspension to the rear axle only (two corner) will reduce the benefits, particularly for on-site levelling, but will improve the ride, the ability to keep up the rear end when using ferry ramps and achieve a level ride height across the rear wheels.

Even the VW T5 and T6 chassis is said to be improved by the addition of full air suspension. Two attributes campervan owners with full air suspension enjoy are the ability to have a lower ride height – perfect to creep under height barriers – and also to raise the vehicle for off-road access.

Pros and cons of full air suspension systems for motorhomes

Pros

  • Improved cornering stability and reduced body roll
  • On-site levelling benefits

Cons

  • Expensive
  • Can eat up valuable payload


Things to consider

While these are all great options, if all you want to do is improve an ageing motorhome’s existing suspension, then uprated springs are a good option. There are options for both front and rear axles and for most base vehicles.

Also, there are levelling systems, which are purely designed to level a motorhome on site. Mainly hydraulic systems, these involve legs that extend from underneath the motorhome to provide greater stability on the campsite as well as a level motorhome.

If fitting full air suspension or air assistance on an older chassis without ABS braking (generally pre-2002 for Fiat Ducatos), a word of warning about front and rear brake equalisation. The pre-ABS equalisation system equates a low rear with heavy loading; with air suspension providing a constant height, the system must be adapted.

Most systems should be maintenance free, but it's worth reading all the literature when you have a system fitted.

Check with the supplier that all the facilities you require are available. A full air suspension system with automatic static levelling should work on a sequence so there’s no strain or distortion to the chassis. For manual operation this is something to be careful of.

Systems vary; in particular, note the difference between the basic air assistance kits. In general, the more you pay the greater the sophistication and the ease of use.

Some companies have a national network of service agents, which can be convenient for installation and any after-fitment problems.

Check if the kit has approval certification from recognised testing bodies like TÜV. As with any vehicle modifications, you should notify your insurance company.

If you have a shaky motorhome, because of a long rear overhang, remember air suspension will not improve static stability. You can add on hydraulic levelling but always ensure the levelling and suspension control systems are compatible.

If air suspension provides all your needs except the rear end stability, then the most economical solution can probably be achieved with Al-Ko’s ClickFix rear steady legs.


Final thoughts

Full air suspension offers a wide variety of benefits both on the road and when static on a site. The benefits of air assistance are more limited. So, it’s all a matter of your individual requirements, your budget and available payload.


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