Unlike some of the trends, tricks and treatments in street rodding that become popular only to fade away as quickly as they arrive, it appears air suspension systems are destined to be as big a part of this hobby as the dropped axle. Air springs have proven to be reliable, provide outstanding ride and handling characteristics and, of course, the adjustability they offer is unparalleled.
In the October and November issues of SRM we looked at the basics of air springs and how to select and install them. This time we're going to look at controlling the ups and downs of air springs.
Basic Plumbing
Like most things having to do with street rods, the system used to inflate and deflate air springs can be simple or complicated. It may be as rudimentary as a tire stem-type inflation valve (like those used on air shocks of the '60s) to manually adjust the air pressure in the 'bags, or as sophisticated as a computer system that automatically adjusts the ride height of the vehicle.
Although it would be possible to alter the air pressure of each air spring with an individual manual-inflation valve, to take full advantage of the adjustability they offer an on-board air source that should be included. That means a compressor, probably a storage tank and some sort of control system will be required, and that will determine how the system is plumbed.
In some cases air springs on the same axle are hooked together. While this keeps things simple and only requires one control valve per axle, there is one drawback: that is the tendency of air to transfer from one side of the car to the other when it leans in a corner, and the transfer of air will make it lean even more. On a light car, or those that have antiroll bars, it may not be an issue. However, plumbing the 'bags individually will eliminate the tendency completely and enhance handling, but it means an individual control valve and airline for each air spring will be required.
Air Lines and Fittings
Generally air spring suspension systems are plumbed with flexible lined. Air Ride Technologies supplies DOT-approved plastic tubing with its kits, and while it is safe and reliable, some builders prefer to use hard lines for appearance sake. And while that is a viable option, in some applications, when using ShockWaves as an example, there will be movement between the shock body and the chassis that must be taken into consideration. For that reason, Air Ride Technologies offers braided line kits to connect the airbags to the hard line to provide that needed flexibility.
While hard lines look trick on a show car, the beauty of plastic airlines is the simplicity of installation. Connections are easily made with push-together fittings. Available in straight, right-angle, and T configurations, all such fittings offered by Air Ride Technologies are DOT approved. Making connections couldn't be easier; the plastic tubing is simply inserted in the fitting. When it bottoms out in the fitting, the tubing is secured with an integral locking collar. The only critical step in the assembly process is to cut the end of the line square, and Air Ride Technologies can even supply a tool to do that job.
One of the most common questions about plumbing air springs is what size line to use. Air Ride Technologies offers 1/8-, 1/4-, 3/8-, and 1/2-inch lines and fittings. So, what's the difference? Simply put--speed. The larger line allows the 'bags to inflate and deflate faster (of course, any or all of the following will help--larger valves, multiple compressors, larger tank capacity and higher air pressures). And while faster height changes are important to some users, a higher volume of air can make it more difficult to fine tune ride height.
Compressors
Think of a compressor as an engine; there are small-blocks and big-blocks and displacement varies (same with compressors). Compressors are rated by the volume of air they pump, the pressure produced, and the amperage drawn. And while all those factors are relevant, another important consideration is the environment it will live in. Air Ride Technologies compressors are sealed for protection so they can be mounted virtually anywhere--not all can make that claim.
Compressors are usually controlled one of two ways. In systems without a storage tank, a multi-function switch with an electrical circuit to activate the compressor and pneumatic valve to inflate the 'bags in the up position and deflate the 'bags in the down position is used. When a storage tank is included a separate pressure switch usually controls the compressor. As soon as the pressure in the system drops to a preset point the switch closes and turns on the compressor, when the pressure in the system reaches the upper limit, the switch opens and shuts off the compressor.
Storage Tanks
For most street rods, particularly those with full air ride systems, a storage tank is recommended. A 2-gallon tank should provide enough capacity to raise a car to ride height without the compressor turning on. For faster rise times, larger or multiple tanks may be used.
Controls
Basically there are two types of controls for inflating and deflating air springs, manually operated pneumatic valves or switches that control solenoids.
Typically, manual valves are mounted to a panel with a pressure gauge; there may be one valve and a single gauge for a pair of 'bags or a pair of valves and a dual gauge. The dual arrangement may be plumbed so each valve controls a pair of 'bags on one end of the car, or each valve controls the 'bags on one end of the car individually. (this is the best arrangement to isolate the 'bags to keep them from transferring air while cornering.)
A more sophisticated means of controlling the 'bags is with solenoids. With this type of system, the dash-mounted switch controls a solenoid that inflates or deflates the air spring. The advantage to this arrangement is under-dash airlines are eliminated. In addition, the solenoids can be remotely mounted in the trunk, as an example, for a cleaner installation.
Air Ride Technologies offers two series of solenoids, the RidePro and BigRed. The difference between them is the amount of air they will flow. For over 80 percent of its customers, Air Ride Technologies recommends the RidePro series. Rise time from the lowest position to ride height is roughly 3 to 5 seconds. For those who want faster height adjustments, the BigRed series is suggested.
A BigRed four-way system will lift the vehicle to ride height in approximately 2 seconds, while a BigRed MAX system will do it in well under 2 seconds. There is, unfortunately, a trade off. The faster the system reacts, the harder it is to make small adjustments in air pressure. If the most precise ride quality and height adjustments are important, go with the RidePro; if speed is the major consideration, use one of the BigRed designs.
RidePro E
Now we're getting into the really sophisticated systems. With the RidePro E, Air Ride Technologies has combined its RidePro solenoids with a computer to control them. Also included is a control panel with membrane style switches and digital readouts that can be flush-mounted on the dash or hidden.
Along with controlling air pressure via the solenoids, the computer makes the RidePro E's "ride-height-on-start feature" possible. Each time the car is started, the computer inflates the 'bags to a programmable, pre-set pressure. If that's not trick enough, an optional remote control is available. A unique key fob allows you to raise or lower your car from a distance, as well as activate the ride-height-on-start function. By the time you're in the car, it's already at ride height, ready to go.
LevelPro
Arguably the most significant development in air spring suspensions since the ShockWave, Air Ride Technologies LevelPro brings the sophistication of factory systems to the aftermarket.
The LevelPro system not only provides all the advantages of air ride systems we've come to expect, but also includes the ability to preset three different suspension heights--low, on the road, and high (for clearing obstacles like speed bumps). Simply punch a button, and the car raises or lowers to a preset level. In addition, the LevelPro also has a leveling feature. As the load in the car varies due to a change in passengers, cargo, or even filling the gas tank, sensors at each wheel send a signal to the computer. In turn, the computer activates the solenoids to increase or decrease the air pressure in each 'bag as necessary. Once the ride height of the car is programmed, the LevelPro will take care of the rest.
Summing It Up
Over the course of the last three issues of SRM, we've looked at the advantages of air springs, shown the considerations necessary to install them, and presented the latest in plumbing and control system options. But if you're still not convinced that air springs are the way to go, take a ride in a car equipped with them. You'll be sold, and we could have saved our breath.
A variety of control panels are available; style is used on the RidePro E. It has membrane buttons and digital readouts for each 'bag. | 
The simplest control is this single paddle switch and individual gauge. It's best suited to help spring installations. | 
This panel uses a dual switch and a single gauge with dual dials. It can be used on four-bag systems with the 'bags on each axle T'd or two 'bags on the same axle. |
An option for individual 'bag control is this four-switch panel with twin dual-needle gauges. | 
A number of panels use digital readouts. This example has dual-bag controls; quads are also available. | 
Storage tanks are available in a variety of sizes. For most street rod applications, 2 gallons is adequate. |
The new RidePro E offers plug-and-play installation, the ride-height-on-start feature, and an optional remote control. Existing RidePro systems can easily be updated. | 
Coming soon from Air Ride Technologies is the all-new LevelPro. The computer uses sensors at each wheel to determine the proper pressure in each 'bag to keep the car level. | 
This is a typical sensor used in the LevelPro system. They are used in pairs and can be installed on one axle or both. |
These ingenious rubber connectors are used to connect the sensors to the axle. | 
The LevelPro sensors are attached to the frame with the arms reasonably level. | 
In this proto-type installation a lower four-bar bolt was drilled and tapped to attach the lower link of the sensor. |
With the four-bar bolt modified, the link was installed. | 
Hooking the sensor to the axle was simply a matter of cutting the connecting rod to length and slipping it in place. An added bonus is the rubber connectors are forgiving with minor misalignment. | 
The brain of the LevelPro system is this small computer. Extensive testing has shown the system to be extremely reliable. |