How does air suspension work?
Your typical air suspension system comes with some unique features and draw backs when compared to a tradition spring and shock system. The common spring assembly in an air suspension is replaced by a rubber balloon of air which simulates the coil spring. This bag surrounds and seals the shock and airbag assembly to be filled with air. Individual lines are ran to each respective air spring to fill and deflate it. These lines can either be made of solid metal which is great for looks and show applications, but also simple polyurethane lines do the job providing the function but not the eye catching form. Air is fed into these systems via either an external compressor which connects and fills the system via an external feeder line. Or you could opt for a more expensive but convenient on board compressor and tank. The compressor setup is usually tucked away in the vehicle’s trunk or spare tire compartment and compresses air and fills up the system with a simple push of a button.
For setups with an integrated compressor, air is drawn in from the outside, pressurized in the tank and then the pressurized air is sent out via the air lines to each air spring to inflate them to the desired pressure/height. This is where one of the downsides of air suspension comes into play, the droning noise of the compressor doing work. Depending on the setup, the noise can be dampened but aftermarket air setups come with a characteristic hum while air is being compressed. Air springs fit a variety of different applications including heavy duty hauling, improving ride comfort over a traditional shock and spring setup and of course adjustable suspension height for show use. As with all things suspension related, every detail has an effect how how your suspension behaves and air springs are no different.
With the inclusion of on board compressors, sensors and electronic controls for your air system, the pressures inside each individual air spring can be adjusted on the fly. This makes daily driving easy for “slammed” cars because they can air up to normal ride height and travel with no problem and then dump the chassis down to the ground once all the driving is done. The added sensors are a benefit to ride comfort too because the system can actively adjust the air spring pressures to provide the most comfortable ride when driving. Some luxury cars come equipped with air springs but due to their complexity the cost for adding that option from the dealer or going with an aftermarket upgrade kit are both significant. Most modern aftermarket upgrade kits don’t require any heavy modification to your suspension and slip right over your existing shock if one isn’t provided to replace the air spring. Hacking up your shock towers and relocating components is a thing of the past.
Maintenance and repairs is where air spring systems fall short from traditional coilover systems. The complex system has multiple parts, each with their own special set of issues. The biggest threat to the air system is actually air itself believe it or not. With the constant heating and cooling of the air with in tank compressors, the air inside the tank forms condensation on the inside of the tank. Water will begin to pool and eventually rusts your tank. With air constantly circulating in your system it carries some droplets of water and rust sludge to other components in the system further damaging them. Properly maintaining your tanks by regularly draining your compression system of air and moisture will prevent this. Some tanks also come with a built in dryer or dessicant to aid in preventing moisture build up. For those that guessed at what a dessicant is, it is a hygroscopic substance used to absorb moisture.
Lines are a major factor. Any damage to a line and you’ve got an air leak in your system which leads to bags that do not inflate properly or at an adequate speed depending on where the damage in the line is. Polyurethane lines would be easier and cheaper to fix than steel due to materials and the amount of work required for the repair. Having the afore mentioned rusty sludge sliding around in your lines isn’t great for them either and could lead to more problems with your lines.
Valves are the gateways for air to enter and leave the system. Damage to a valve could mean one air spring not being able to inflate or deflate due to an inoperable valve, along with just random discharging of the air in the system if a valve opens without instruction. These can also rust from moisture inside the system
Solenoids Control the signals sent from the controller to the valves and control the flow of air in the system. A damaged solenoid means air is not able to flow in the proper direction.
Compressor damage will cripple your whole system in most cases as the ability to compress air and fill the air springs will be hindered or lost completely. Rust can also damage compressor components leading to undesired performance.
All of these these components are costly to replace due to the various parts needed and the time it takes to repair the complete system. The upside to all of this is that these components rarely fail in a properly maintained system. Most people assume that the rubber sleeve that surrounds the shock would be the first component to fail because of the abuse it takes but this part surprisingly lasts the longest. As long as the air spring sleeves are a decent distance from a heat source and aren’t rubbing on anything, they will most likely outlast your car.
Once you’ve got a fully functional system, the next step comes in determining how you’re going to read and regulate the air pressure in your bags. Systems come with one of two ride management systems.
Pressure based systems read the air pressure present in each air spring to determine what the ride height of the vehicle is. This system is fairly accurate but the pressure in the air spring changes with normal driving during cornering and adjusting to bumps and holes in the road. This short change in pressure could lead the system to adjust the ride height of the vehicle when it doesn’t need to be. Adding extra weight can also confuse the system and it will adjust the ride height based on the pressure values of the air springs instead of determining the proper ride height via ground clearance.
Ride height based systems use a series of sensors to ensure the vehicle stays at a predetermined ride height that is accurately measured via a slew of sensors. This has an advantage over pressure based systems that make assumptions of what the ride height is based on the pressure inside the air springs instead of the actual ride height. These sensor based systems are precise enough to also be used for performance applications and provide some performance benefits over coilovers.
Air is distributed to the air springs via the valve system which come in two configurations. 2-way (4 valve) and 4-way (8 valve) the difference in these systems comes from how air is distributed to the air springs from the compressor.
2-way systems use one channel to fill up two bags. This means two bags are inflated via a single air channel and the pressure is shared between them. This setup allows air to travel between the linked air springs which causes pressure changes while driving. Compression of one air spring will force air to the linked air spring. This causes unwanted changes to your air spring pressures for that whole half of the system. Couple these unwanted pressure changes with a pressure based ride height system and your vehicle will adjust it’s ride height to return back to normal ride height pressures which aren’t always correct.
4-way systems are the gold standard when outfitting your vehicle with air and provide benefits over a 2-way system. The 4-way system provides each individual air spring with a dedicated line of air. This means that pressure changes in one corner aren’t going to affect the pressures in the other springs, similar to a coilover system. Individually fed air springs allow for adjustment of each spring individually and also helps track down any problems in the system.
Most vehicles that come equipped with stock air bag systems are more geared towards the comfort of the occupants over how little body roll you can achieve when cornering at 60mph. The ride of air springs is noticeably smoother than that of a coilover system thanks to the literal cushion of air your ride is sitting on. This knowledge leads most to believe that air springs would provide too soft of a ride to provide any kind of performance benefits over coilover systems but technology has come a long way to improve that and as with anything suspension related, your air springs aren’t the only things affecting how your ride handles.
A performance oriented suspension, has of course performance oriented parts and an air spring system is no different. You still need a good supporting cast for your air springs, most importantly properly selected dampeners to deal with the forces acting on your suspension. An amazing air spring system will fall far short of expectations if this is the only upgrade you invest in when looking to get more performance out of your suspension. Choosing the proper components when setting up your air suspension for the track is essential to achieve the desired performance.
At the heart of a performance oriented setup is the shock or dampener that will be the heart of the air spring assembly and an integral part to how your suspension performs. Do not skimp on a good dampener set for your air springs! With the proper components you will be able to get the most out of your air suspension. Just like higher end springs, air springs are progressive, meaning the spring rates increase the more the spring compresses. Another benefit is the ability to adjust your spring rates, this is usually done by airing up the springs. Airing up your springs will raise your ride height, usually not ideal for track situations, but that is where your other suspension components come into play to setup your ride properly. A performance oriented shock will allow you to adjust the ride height by making adjustments to the shock assembly, this is how you can increase your spring rates without actually raising your ride. Setting the shock for a lower ride height will stop the air spring from raising the ride height further than the shock allows, in turn building more pressure in the air spring and allowing you to adjust your ride height AND your spring rates. This type of setup would give you not only the stability you’ve come to expect from a high end coilover system but also the ability to adjust ride height and spring rates on the fly. As a side note a 4-way system should always be used so each air spring assembly can react independently to changes in the road and the various lateral forces experienced during racing. A 2-way system would see air traveling between the two connected air springs and causing unwanted changes in spring pressure.
The Wrap Up
Automotive technology has come a long way and air suspensions have benefitted from the passing of time. The systems have become cheaper and installation for aftermarket systems has been simplified to the point where any competent at home mechanic can do the install. You’ve got a lot of options to consider when switching to an air bag system but the two main things you should look for are support and service after the purchase and the build quality of the system. Being able to contact the manufacturer to get your specific questions answered is a godsend along with a direct line of contact for other components. As with all things you get what you pay for and suspension components are no different. The benefits of this system are mainly in the adjustability of it all. Being able to change your ride height with the touch of a button as opposed to popping your trunk and hood, taking your wheels off and getting in there with those funky wrenches is a nice creature comfort offered by air springs. You also have the ability to set your suspension to feel more comfortable or performance oriented by not only adjusting your dampening but your spring rates too with an air bag system also. Cost and the fear of repairs seems to be the deterring factor for a large group of people. Repairs are few and far between in a well maintained system and unless you’re abusing your system you shouldn’t have anything to worry about. Always be sure to do your research before upgrading to an air suspension and don’t skimp on the supporting components to the system. Overall upgrading to air springs is not a bad choice as long as you have a clear idea for how they will be used and of course the capital to upgrade.