Every car has some combination of springs, shocks, bars, or links that suspends its chassis, body, engine, and drivetrain above its wheels. Get rid of any of it and the ability to accelerate, turn, and stop-and do so in relative comfort-will go to shit. Trouble is, most of those characteristics are at odds with one another, which is exactly why you know less about suspension tuning than just about anything else.
Air suspension systems seem even more mysterious but, as it turns out, they aren't a whole lot different. Most modern suspensions are made up of a coil spring that slips over a shock or is positioned near it. At its core, an air suspension really just does away with those coil springs for flexible, pressure-filled bags of air that are typically made of the same sort of rubber as your tires. At the touch of a button, the bags can be inflated or deflated, instantly altering ride height and how the suspension performs.
Haters have been pitting air suspension systems against more conventional coil-spring suspensions for years, often with little sound reasoning behind any arguments. A proper suspension isn't as subjective as you think, either, and can be measured by how well it takes advantage of its tires' traction capabilities, how evenly traction is distributed from front to rear, and how responsive it is to the driver's steering, braking, and throttle inputs. Pass those tests and it doesn't really matter whether we're talking about tightly wound coils of steel or rubber-formed pillows of air.
At the core of any air suspension system is its bags, or air springs. Here, rubber bellows that feature metal plates at each end slip over the shocks, similar to a coil spring. Like coil springs, air springs are progressive in nature, which means increased compression results in a stiffer spring. The ability to alter an air spring's rate at any moment means the potential for better performance or ride quality just got a whole lot easier.
Chances are, fitting an air spring kit to your car just got a lot easier, too. The whole process has come a long way over the last five years, according to Air Lift Performance's Corey Rosser. "With technological advances in air springs and air control, an air suspension system today is a very comparable option to a coilover system," he says. Gone are the days of chopped-up shock towers and relocated suspension bits in hopes of fitting some billowy bags in place. Today, hollow bellows that allow shocks to slip through themselves make mounting them into most cars easier than it's ever been. Today's kits allow you to leave the shocks in the factory locations and, for the most part, bolt in much like any conventional coilover system would.
There's a whole lot more to a proper air suspension system than four bags worth of hot air, though. Any kit worth your consideration is made up of all sorts of other components. It starts with an onboard air compressor that's powered by the car's electrical system and is able to inflate each bag on demand. The compressor feeds the springs individually using flexible, polyurethane lines or, in some cases, custom-bent, stainless steel tubing (you'll see the top show cars rocking hard lines). Most of the time, a separate air tank is integrated that helps instantaneously increase and maintain air pressure within the system and allow for smoother transitions between large pressure changes. Both components are typically mounted in the trunk, sometimes in a custom enclosure, but they can also be hidden underneath the chassis or attached to the unibody or frame.
The compressor works like any other air pump, drawing outside air into its internal tank, where it's pressurized and sent out its other end. Somebody's got to tell it when to pump and how much air to allow past itself, though, which means some sort of driver-actuated controller has to be integrated into the system. Here, manual or electronic controllers are available that can be mounted near the driver or accessed from a smartphone app in some cases for easy, on-demand ride-height adjustments.
Once the system's installed, you've got to determine whether or not you'll adjust ride height based on air pressure or through a series of sensors. Pressure-based systems rely on a given value that you know positions your car at a particular ride height. But we must warn you, pressure sensors aren't always accurate, and weight changes can still affect ride height. For example, plop a few hundred pounds onto the back seats and watch the ride height drop. As air springs compress from added weight, pressure-based systems recognize this and compensate by reducing air pressure back to its original value, which results in exactly what you think it wouldn't-lowering your car even more. Unwanted changes can also happen when weight's thrown around while cornering or when going up or down a hill.
Electronic systems that rely on a series of sensors to establish and maintain ride height are far more accurate and don't care whether or not there's 150 pounds' worth of pressure inside those air springs. Here, sophisticated sensors placed underneath the chassis monitor ride height and relay that information back to the controller, ensuring ride height remains where you want it, despite pressure.
Just like with coil springs, an air spring suspension works best with the right supporting mods. Most experts recommend going on the soft side when setting up air spring rates, and instead focusing on the right shocks to address oscillations and the right sway bars to minimize body roll.
To Slam or Not to Slam
- On-the-fly ride-height and handling adjustability. Duh!
- Preserve expensive, low-hanging body components and prevent chassis damage.
- Progressive-rate air springs, just like your coils.
- Adjustable spring rates.
- Highly versatile.
- No other way to obtain a slammed ride height and remain functional.
- Instantly adapt to increased weight changes.
- Decrease ride height without sacrificing ride quality.
- More expensive than coil-spring suspensions.
- Installation process more complex.
- Installation process more expensive.
- More components required.
- Permanent chassis modifications necessary in some instances.
"But the bags might pop, bruh."
According to air suspension installation experts Boden AutoHaus' Josh Esfahani, this is a crock often dealt by those unfamiliar with air. "Yeah, maybe if they're installed wrong and are rubbing up against something, there might be a problem," he says. Otherwise, popped air springs are little more than figments of the uninformed's wild imaginations.
"An air suspension will never handle as good or be as reliable as a set of coilovers."
Function Form's Preston Dawson says that just isn't the case anymore. A properly designed system that incorporates the appropriate shock characteristics can handle just as well as many conventional suspensions would. "If you pick out the proper components that work together, you can get reliability as good as any static coilover setup," he says And according to Air Lift Performance's Corey Rosser, performance isn't compromised, either: "We've spent thousands of hours testing and improving our product to the point that it can handle the same kind of beating that people give their coilovers." "Air suspension is for show cars."
AirREX's Marshal Lum says a large percentage of the company's kits are sold to enthusiasts who'll never see the likes of a body kit or circus-colored engine bay, much less a car show. He added that customers have been using AirREX systems on street cars and dedicated track cars for years. Esfahani says the same thing: "Air springs used to be for guys who wanted to go lower than low. Now guys are racing with these."
Performance vs. Luxury: What's the Diff?
It's all in the shocks. They're the primary difference between an air system designed for a sedan with velour window curtains or a 550hp coupe on R comps. Like coil-spring suspensions, the shocks' compression and rebound rates, damping forces, and cooling capabilities determine whether or not the system as a whole is best suited for donut shop parking lot meets or the road course. The air springs, compressors, lines, electronics, and everything else will never turn a good shock into a bad one.
Performance-based systems typically feature the same sort of shocks you'd find on higher-end coilover suspensions. Here, height-adjustable threaded bodies, adjustable damping, camber and caster adjustability, and mono-tube construction are common signs of a performance-based shock. The ability to adjust a shock's damping along with an air spring's rate can allow for unmatched levels of tunability when compared to coil-spring suspensions. In other words, the same car can go from soft and comfortable to firm and precise in just a few seconds.
An air spring's rate is dependent upon how much pressure's inside, though. Increase the pressure to arrive at the sort of spring rate you'd want for racing, and you just raised the car. If you think this sounds counterintuitive to setting your car up for the track, you'd be right. This is where shocks with threaded bodies that allow for ride-height changes on their own become even more important.
We asked a few air companies what should noobs be most concerned about when shopping for an air system.
Marshall Lum, AirREX: Consumers must understand their chassis first. Some chassis must be modified, however, most AirREX systems will get you as low as possible without major modifications.
Preston Dawson, Function and Form: Consumers should invest in a system designed to work together. Are the bags made to work with the struts? They should look at what type of bag a company uses and understand the pros and cons of each type. Does the company help with tech support? Because you'll need it. Corey Rosser, Air Lift Performance: There are a lot of air suspension options to choose from. The biggest thing a consumer can look for is the quality of the product and customer service.
Function and Form ON AIR Conversion Kits: Function and Form is famous for its coilover suspensions and is now among the first to integrate its air springs into existing applications. That means you can buy a set of coilovers today and replace those coils for air springs next year. The conversion requires no cutting, welding, or trimming and is fully reversible. Manual and electronic controllers are sold separately and integrate into all of Function and Form's ON AIR systems.
Air Lift Performance/Performance Series: These guys were among the first to offer kits for cars like Honda's ninth-generation Civic. Its Performance Series systems include everything you'll need, along with manual or electronic management systems. Kits are made up of 30-way damping, fully threaded, mono-tube shocks, double-bellow air springs, and all of the appropriate lines, clamps, and fittings needed to connect it all up. Manual management systems are made up of a 200-psi-capable air compressor, four-gallon air tank, and the appropriate hardware to hook it all up. Electronic systems feature Air Lift's AutoPilot V2 controller and manifold that allow for instant and personalized adjustments. The company says its ninth-gen Civic kit is good for nearly a 4.5-inch drop.
AirREX/Wireless Control Combo Kits: AirREX was founded in hopes of delivering performance-based air spring systems to the public. Its kits are based off of fully threaded, 12-way-adjustable shocks that feature built-in brackets and mounts that make installation a bolt-on deal. AirREX's digital air management solution is based off of an electric solenoid manifold that lets users dial in the rate at which the car can be lowered or raised, all from a wireless controller.