Air suspension on trucks has huge advantages, and a few disadvantages. Most new trucks come with an air suspension option (if not as standard), and it’s available on trailers, too.

If you’re considering air suspension on a truck or trailer, here are the advantages.

Reduced noise, vibration and harshness

It’s much more comfortable for the driver – noise, vibration and harshness causes driver fatigue and discomfort, so if you can reduce this, it’s safer.

It’s easier on components – reduced vibration and harshness means better wear on other components in the truck. Trailers tend to last longer when on air suspension as the components don’t suffer as much vibration.

In short-wheelbase trucks it reduces the tendency to bounce over rough terrain when the truck is empty.

Improved fuel consumption

Some air suspension systems can optimise the ride height based on the speed of the truck and whether it’s laden or unladen. Unladen trucks usually sit higher because there’s less weight pushing the suspension down, but this is bad for wind resistance. A lower ride height means better aerodynamics because it reduces the wind resistance.

Because the suspension is better suited to the road surface, higher corner speeds can be achieved leading to time saving on routes with a lot of turns.

There is some trade-off in the fuel benefits in the form of a small amount of extra fuel used to run the air suspension compressor when needed.

More versatile on certain types of terrain

It is sometimes height adjustable – adjustability can help with different types of loads, plus air suspension sometimes comes with a ‘kneel’ mode to help with loading, and a ‘raise’ mode to help clear bumps and rough terrain.

It is sometimes adjustable for feel, enabling better drivability; a driver can choose a softer ride for motorway cruising, or a harder ride with better handling on roads which are more demanding.

Air suspension is more consistent and even for all wheels. Systems can ensure the truck is level side-to-side in the case of loads which are difficult to load evenly, and it can reduce body roll in corners. You can effectively eliminate suspension sag.

Because the suspension can be levelled with any load (using a height control valve), it allows a trailer to be built to a higher top and lower floor while maintaining consistency and ensuring that a trailer is never over-height.

More versatile for some loads

Fragile loads such as large panes of glass benefit from being carried on a truck or trailer with air suspension as there’s less risk of breakages. Other loads benefit from air suspension, too, meaning that a trailer becomes more versatile and therefore is less likely to be running empty.

Air suspension can increase the ability to transport some loads by creating better grip through levelling the suspension.

Improved tyre life

More effective suspension means less vibration that has to be accommodated by the tyre and this leads to better tyre wear.

Some air suspension can lift unused axles, further improving tyre life.

Better resale

Air suspension trailers have better resale value.

Less damage to road surfaces

While you don’t get any RUC benefits from running air suspension, there are actual benefits to the road network as it causes less damage to the road and bridges. Less vibration is transmitted into neighbouring buildings and structures.

Less load shifting and damage

When there’s less vibration through the suspension, it’s better for the load. While improvements in packaging and load restraint have reduced the amount of damage caused to loads on bumpy roads, the smoother ride of air suspension adds that extra level of cushioning.

What are the disadvantages of air suspension?

Durability

Leaf spring suspension is more durable than air suspension – it’s common to see historic trucks running the same leaf suspension setup they came out of the factory with 60 years ago. Leaf spring suspension doesn’t usually need much maintenance – some retorquing of the leaves – but air suspension can, and it’s more complex. Some companies report maintenance on air suspension to be three times the cost of leaf suspension over a 10-year period.

They will eventually need some maintenance to fix any leaks. You may need to keep a spare air line and other parts in case you need to make running repairs.

More costly

There’s a small fuel overhead of running the compressor occasionally to pump them to the correct pressure, but the main cost is the initial purchase. Trucks with air suspension have better resale value, though. Companies running large fleets of small local delivery box trucks where the margins are very thin won’t get the aerodynamic advantage of air suspension, and the drivers are in and out of the cab all day and are therefore less sensitive to the kinds of long periods of vibrations that line haul drivers experience on New Zealand’s roads.

Operation

Operators need to understand how to set and use air suspension to avoid damage. Items that can be damaged include the air hoses which can break loose and rub against the airbags which in turn causes abrasions and holes in them.

Air suspension is heavier than leaf suspension and therefore fuel economy benefits aren’t always experienced. Overall fuel economy is a combination of many factors, too.

What is air suspension?

Air suspension replaces coil springs or leaf suspension with airbags made of rubber and polyurethane which are inflated by a compressor. The bags are inflated to a certain pressure to mimic springs.

Over the last decade or so air suspension has become popular in the custom automobile culture: street rods, trucks, cars, and even motorcycles may have air springs. They are used in these applications to provide an adjustable suspension which allows vehicles to sit extremely low, yet be able rise to a level high enough to maneuver over obstacles and inconsistencies on paved surfaces. These systems generally employ small, electric or engine-driven air compressors which sometimes fill an on-board air receiver tank which stores compressed air for use in the future without delay. It is important that the tank is sized for the task and can be calculated using a specific formula involving the compressor output, standard atmospheric pressure and compressed pressure.

High-pressured industrial gas bottles (such as nitrogen or carbon dioxide tanks used to store shielding gases for welding) are sometimes used in more radical air suspension setups. Either of these reservoir systems may be fully adjustable, being able to adjust each wheel's air pressure individually. This allows the user to tilt the vehicle side-to-side, front-to-back, in some instances "hit a 3-wheel" (contort the vehicle so one wheel lifts up from the ground) or even "hop" the entire vehicle into the air. When a pressure reservoir is present, the flow of air or gas is commonly controlled with pneumatic solenoid valves. This allows the user to make adjustments by simply pressing a momentary-contact electric button or switch.

The installation and configuration of these systems varies for different makes and models but the underlying principle remains the same. The metal spring (coil or leaf) is removed, and an air bag, also referred to as an air spring, is inserted or fabricated to fit in the place of the factory spring. When air pressure is supplied to the air bag, the suspension can be adjusted either up or down (lifted or lowered).

For vehicles with leaf spring suspension such as pickup trucks, the leaf spring is sometimes eliminated and replaced with a multiple-bar linkage. These bars are typically in a trailing arm configuration and the air spring may be situated vertically between a link bar or the axle housing and a point on the vehicle's frame. In other cases, the air bag is situated on the opposite side of the axle from the main link bars on an additional cantilever member. If the main linkage bars are oriented parallel to the longitudinal (driving) axis of the car, the axle housing may be constrained laterally with either a Panhard rod or Watt's linkage. In some cases, two of the link bars may be combined into a triangular shape which effectively constrains the vehicles axle laterally.

Often, owners may desire to lower their vehicle to such an extent that they must cut away portions of the frame for more clearance. A reinforcement member commonly referred to as a C-notch is then bolted or welded to the vehicle frame in order to maintain structural integrity. Specifically on pickup trucks, this process is termed "notching" because a portion (notch) of the cargo bed may also be removed, along with the wheel wells, to provide maximum axle clearance. For some, it is desirable to have the vehicle so low that the frame rests on the ground when the air bags are fully deflated. Owners generally choose between having their cars 'tuck' their wheels into the arches when their air suspension is fully lowered or alternatively they can choose to go for 'fitment' which in partnership with stretched tyres sees the arch itself fit in between the tyre and rim.

Air suspension is also a common suspension upgrade for those who tow or haul heavy loads with their pick-up truck, SUV, van or car. Air springs, also called "air helper springs," are placed on existing suspension components on the rear or front of the vehicle in order to increase the load capacity. One of the advantages of using air suspension as a load support enhancement is the air springs can be deflated when not towing or hauling and therefore maintaining the factory ride quality.

Electronic Air Suspension

Electronic Controlled Air Suspension (ECAS) is the name of the air suspension system installed on the Range Rover Classic in 1993 and later on the Range Rover P38A. It was developed in the early 1990s by the company now known as Dunlop Systems and Components Ltd in Coventry, UK.

ECAS provides variable-height suspension for on- and off-road applications. The five suspension heights typically offered by ECAS are (from lowest to highest in terms of height) "Loading," "Highway," "Standard," "Off-Road," and "Off-Road Extended." Height is controlled automatically based on speed and undercarriage sensors, but a manual ride height switch allows control over the suspension by the driver. The "Loading" and "Off-Road" heights are available only at speeds typically less than 35 miles per hour (56 km/h). The "Highway" setting is not available manually; it is set when the vehicle moves at over typically 50 miles per hour (80 km/h) for over 30 seconds. Unlike a mechanical spring system (where deflection is proportional to load), height may be varied independently from the load by altering the pressure in the air springs.

The air springs were designed to provide a smooth ride, with the additional ability to raise the body of the vehicle for off-road clearance and lower it for higher-speeds road driving. Mechanical springs, for which deflection is proportional to load, cannot do this; with ECAS height is largely independent of load. The developers of ECAS also designed LoadSafe, a related system to ascertain load and change in load on an LCV type vehicle fitted with air springs.

The system comprises:

• a vulcanised rubber air spring at each wheel
• an air compressor, which is typically located in the trunk (boot) or under the bonnet
• a compressed air storage tank may be included for rapid "kneel", storing air at ~150psi (1000 kPa), note (1psi=6.89kPa)
• a valve block which routes air from the storage tank to the four air springs via a series of solenoids, valves and many o-rings
• an ECAS computer which communicates with the car's main computer the BeCM and decides where to route air pressure
• a series of 6 mm air pipes which channel air throughout the system (mainly from the storage tank to the air springs via the valve block)
• an air drier canister containing desiccant
• height sensors ideally on all 4 vehicle corners based, typically, on resistive contact sensing to give an absolute height reference for each corner of the vehicle.
• Dunlop Systems and Components Ltd have continued to develop the products to the point where the Electronic Control Unit (ECU) is now able to fit under the vehicle floor. The control valves are much smaller and lighter and they produce their own range of compressors.

Multi-Chamber Air Suspension

The Multi-Chamber air suspension is a suspension capable of controlling the spring characteristics of the air suspension step by step.

Common Air Suspension Problems

Multi-Chamber air suspension applicated on the Genesis G90 consists of three chambers. Three chambers are used for a smooth ride, and one chamber is used for a dynamic driving feeling. A solenoid valve located between each chamber and a separate electronic control unit oversees the control process. In addition, the basic minimum ground height of 148mm is divided into four stages: high, normal, low, and ultra-low according to the driving mode, driving speed, and driving environment. depending on the driving mode, driving speed, and driving environment. And it informs the driver of the garage control through the infotainment screen. The speed bump control, the hump control, the slope control, and the high-speed driving control functions are activated under the air suspension control.

Air bag or air strut failure is usually caused by wet rust, due to old age, or moisture within the air system that damages it from the inside. Air ride suspension parts may fail because rubber dries out. Punctures to the air bag may be caused from debris on the road. With custom applications, improper installation may cause the air bags to rub against the vehicle's frame or other surrounding parts, damaging it. The over-extension of an air spring which is not sufficiently constrained by other suspension components, such as a shock absorber, may also lead to the premature failure of an air spring through the tearing of the flexible layers. Failure of an air spring may also result in complete immobilization of the vehicle, since the vehicle will rub against the ground or be too high to move. However, most modern automotive systems have overcome many of these problems.

Air line failure is a failure of the tubing which connects the air bags or struts to the rest of the air system, and is typically DOT-approved nylon air brake line. This usually occurs when the air lines, which must be routed to the air bags through the chassis of the vehicle, rub against a sharp edge of a chassis member or a moving suspension component, causing a hole to form. This mode of failure will typically take some time to occur after the initial installation of the system, as the integrity of a section of air line is compromised to the point of failure due to the rubbing and resultant abrasion of the material. An air line failure may also occur if a piece of road debris hits an air line and punctures or tears it, although this is unlikely to occur in normal road use. It does occur in harsh off-road conditions but it still not common if correctly installed.

Air fitting failure usually occurs when they are first fitted or very rarely in use. Cheap low quality components tend to be very unreliable. Air fittings are used to connect components such as bags, valves, and solenoids to the air line that transfers the air. They are screwed into the component and for the most part push-in or push-to-fit DOT line is then inserted into the fitting.

Compressor failure is primarily due to leaking air springs or air struts. The compressor will burn out trying to maintain the correct air pressure in a leaking air system. Compressor burnout may also be caused by moisture from within the air system coming into contact with its electronic parts. This is far more likely to occur with low specification compressors with insufficient duty cycle which are often purchased due to low cost. For redundancy in the system two compressors are often a better option.

In Dryer failure the dryer, which functions to remove moisture from the air system, eventually becomes saturated and unable to perform that function. This causes moisture to build up in the system and can result in damaged air springs and/or a burned out compressor.