GEM's guide to air suspension

Pneumatic suspension is fitted to a surprisingly large quantity of cars, including expensive off-road vehicles. Yet, automotive air suspension requires annual checks and maintenance. Consider also that neglect of one component can damage associated parts, leading to a much higher repair bill. If you drive a car with an air suspension fault, it also can be dangerous.

What is air suspension?

Automotive air suspension replaces conventional coiled metal springs with pneumatic-filled bags that support the vehicle's weight.

The benefits and drawbacks of air suspension

Self-levelling is a major advantage. This not only stops the vehicle from looking as though its suspension has collapsed, when carrying heavy weights, but it also preserves optimum suspension geometry and handling characteristics. This can be especially useful, when towing. Some less expensive cars, such as the pre-2013 Citroën C4 Picasso, employ self-levelling air suspension on the rear axle alone.

Self-levelling systems can also vary the ride height, especially on performance cars. Aerodynamics and fuel consumption can be improved, by bringing the car closer to the ground automatically at motorway speeds. Off-road vehicles also benefit from the owner being able to raise the suspension to clear obstacles, without damaging the vehicle's underbelly.

A more comfortable ride is the main benefit. The cushioning effect of compressed air, contained within a flexible air spring, insulates the cabin more effectively against bumps, vibration and noise.

More sophisticated systems incorporate active damping, to reduce the front end from dipping under braking. It also controls the car from rolling to one side excessively, while cornering.

The main disadvantage is cost. Air suspension is more expensive to repair and maintain. Many types also require specialist knowledge to identify faults and repair them cost-effectively.

What is the difference between air suspension and hydraulic suspension?

Try not to confuse air suspension with hydraulic suspension. Air suspension uses air. Hydraulic suspension uses fluid.

Some manufacturers employ both systems. For instance, Mercedes-Benz's AIRMATIC utilises pneumatics, whereas the faster-reacting ABC (Active Body Control) employs hydraulics.

How does air suspension work?

The air springs are flexible air bags, produced mainly from a special flexible rubber material. Air is pumped into them by an electric air compressor and the vehicle height is regulated by electronic sensors. Air pressure flows in and out of an electric valve block and the whole system is regulated by an Electronic Control Unit.

Note that an air strut contains an integral damper (shock absorber); an air spring does not.

Maintenance tips and checklist

If you are not mechanically minded, the main tip is to have any dashboard-related fault addressed as soon as possible. Most problems are caused by air leaks and ignoring them can cause premature wear of other components (such as the compressor).

Again, you do not need to be an expert to check if the system is healthy. Walk around the vehicle and check if any one corner looks lower than the others, after an overnight stop. If you notice more than a 2.5cm difference, measured between the top of the tyre and the bottom of the wheelarch, contact a garage.

Routine maintenance checks depend largely on the requirements set by the car manufacturer. Therefore, prioritise those instructions. GEM recommends an annual inspection of the rubber air springs, especially. Any perished air spring should be replaced in axle pairs; do not wait until they have holed. Damaged, or leaking, pipework should also be renewed.

What goes wrong with air suspension?

Air leaks are the most common issue. Pressure tends to escape from air springs, because the flexible material splits over time and mileage. This causes the air compressor to work longer to compensate.

This can cause overheating, which damages not just the compressor but also the air lines. In many cases, the suspension ECU detects a fault and cuts power to the compressor. However, this results in the suspension depressurising to its lowest ride height, making the car unsafe to drive.

A failed relay also causes the compressor to run continually and overheat. This explains why it is advisable to replace the relay at the same time as a compressor.

Air suspension systems tend to utilise conventional shock absorbers ('dampers'), too. These fail in the usual manner. Not only do they become less effective over time but they also can leak.

When replacing leaking air springs and failed dampers, avoid replacing one at a time. They should be renewed in axle sets to preserve safe handling and braking.

Our accompanying blog on air suspension shows the most common checks and repairs that you can conduct.

How much does it cost to repair, or replace, air suspension components?

This depends entirely on your make and model, the type of fault and the ability of your garage to pinpoint the fault accurately. It is also worth comparing prices between genuine manufacturer parts and those made to equivalent standards by a quality supplier.

It is worth noting that Arnott is a well-established quality supplier that makes replacement air suspension parts but redesigns certain aspects to make fitting quicker, easier and, therefore, less costly.

Can I adjust the ride height of my car with air suspension?

Check your owner's manual for instructions on raising ride height and heed any driving instructions, accordingly.

Can I upgrade my car to include air suspension?

Yes - but it is an involved and costly job. We advise that you consult a specialist parts supplier, or knowledgeable automotive modification specialist, to see whether such a modification would be desirable and safe.

It is more usual to convert cars with air suspension to conventional coils, as a cheaper option to repairing the original faulty system.

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