AIR SUSPENSION TERMINOLOGY
Air Spring The rubber bladder assembly that replaces the metal coil, leaf, or torsion spring in a vehicle suspension system, often referred to as an Air Bag.
D.O.T. is short for Department of Transportation. Certain fittings, tanks, and lines are D.O.T. approved and meet higher quality standards and fail safe designs in order to comply.
F.B.S.S. is short for Front, Back & Side to Side. This is the same as saying individual control over each air spring. At AccuAir, we call these systems “4-way”.
P.T.C. is short for Push-to-Connect. P.T.C. fittings accept a special plastic airline that simply pushes into the fitting and seals with an O-ring located within the fitting. The fitting’s collet tightens on the airline automatically and increases its force as pressure increases. To disconnect the airline from the fitting, you must first push the collet and airline all the way IN, then keep holding the collet IN while you pull the airline OUT. Note: a 3/8” open-ended wrench is a handy way to hold the collet IN, while you pull on the airline OUT.
Ride Height is the height that you drive the vehicle at, (sometimes called driving height). This is the height where you will have the vehicle aligned.
Rubber Bellow is the rubber part of the air spring. The metal end caps are usually referred to as top and bottom “plates”.
Spring Rate describes the stiffness of a spring usually measured in lbs/in (pounds necessary to compress the spring by one inch). Almost all air springs have a progressive spring rate, which means that they get stiffer the more they are compressed.
GENERAL AIR SUSPENSION FAQ
Q: Why Air Suspension?
A: Level your load – passengers, fuel, cargo, trailers, etc. Adjust the height of your vehicle on the fly – improved appearance, obstacle clearance, ease of loading, etc. Get an exceptional ride quality regardless of load – read the next Q/A for the explanation. Get amazing handling stability and performance due to the inherent progressive spring rate that Air Springs offer.
Q: How did Air Suspension begin?
A: First, some interesting history that explains it all; heavy transit buses in the 1930’s were in desperate need for a leaf spring replacement. Passengers that rode the bus from the start of the route would complain about the harsh ride that they experienced before the other passengers got on. This was due to the inherent drawback of all leaf springs; in order to be able to carry the heavy load when the bus was full of passengers, the leaf springs had to be massive and very stiff. Yet, this resulted in an extremely harsh ride when the bus only had a few passengers on it, (similar to today’s factory pickup trucks that “buck” on sectioned freeways while they are unloaded). Air Suspension provided the perfect solution. When the bus was empty, a mechanical leveling valve let air out of the spring to keep the bus at the designed height. Once passengers loaded the bus, the leveling valve added air pressure to the air spring to level the load. This extra pressure also served to increase the stiffness of the air spring. Now the bus had the same ride quality no matter how many people were on it. This simple yet extremely advantageous ability – officially called load capacity vs. ride decoupling – helped the air spring find its place on heavy trucks, trains, and eventually passenger cars. The basic design of the rubber air spring hasn’t changed much over the last 80 years, yet the technology behind the systems that control the air springs have improved tremendously. These advancements have brought improved reliability and capability to Air Suspension and helped the list of applications and uses grow to its current state.
Q: What if an Air Spring blows out while I am driving?
A: This only happens if an air spring or airline is installed INCORRECTLY! If the rubber bellow is rubbing on a metal object during operation, or too close to extreme heat, a rupture will eventually occur. If an airline is installed where it can chafe on a sharp object, or too close to extreme heat, it will eventually fail. Yet, when installed correctly, an Air Suspension System will easily outlast the life of the vehicle. If you’re still skeptical, start looking at all of the truck and trailers that you pass on the freeway and notice the massive Air Springs that hold them all up for millions of miles.
Q: Can I adjust the Spring Rate of my air springs along with the height?
A: Yes, but the Spring Rate will be directly connected with spring height. As you raise the air spring’s height, you will also be increasing the air pressure inside, thus increasing its Spring Rate. Unfortunately, this is opposite from what most of us would want for performance applications, (low and firm for handling, high and soft for mobility). One way to adjust the relationship between Spring Rate and vehicle height is to change the mechanical installed height of the air spring, or make it adjustable. Another way to reduce the spring rate is to add an accumulator tank plumbed in parallel with the air spring (sometimes referred to as a “ping tank”). When you purchase a complete Air Suspension System from AccuAir, you can rest assured that the spring rate and overall ride quality has been optimized for your application. AccuAir and our Industry Partners focus on providing the best possible balance between ride quality, handling characteristics, and ease of installation for your vehicle.
Q: What are Fast Bags?
A: The term Fast Bags means that the Air Suspension System raises and lowers very quickly. The device that determines the speed is usually the solenoid-valves, (although the plumbing size must also be larger to flow enough air to and from the air springs). Most Fast Bag systems use (8) individual 1/2” (or larger) orifice, brass pilot-operated valves mounted near each air spring, with 1/2” or larger airline throughout the system. These setups will usually raise or lower the vehicle in less than 1 second each direction. The result is a very abrupt motion that is unarguably hard on the vehicle and suspension components. We don’t promote these systems for the following reasons:
Most of our customer’s would never want their car to move this abruptly.
The individual valve arrangement consumes a lot of space (2 individual valves take up the same space that the entire AccuAir VU4 4-Corner Valve Unit does).
The individual valves require way too many fittings and almost always leak.
Because there are more parts in a pilot-operated valve, they are usually less dependable than a direct driven valve like the VU4.
Pilot-operated valves have a long minimum on time and they are usually large and fast, causing the minimum motion increments for the vehicle to be greater than 1”, which makes setting accurate ride heights very difficult, (although the e-LevelTM System does an amazing job at it).
We feel that the VU4 is the perfect solution to all of these problems and makes for the best overall air suspension system possible. The speed that the VU4 yields is quick, but not radical. In the last few years we have sold a lot of VU4’s to customers that were tired of their large individual valves and became much happier with their entire system after the swap, see Customer Testimonials.
Q: I have heard that it is impossible to have a vehicle with Air Suspension that doesn’t leak, is this true?
A: No. We have found that pipe threads are the most common leak point. Our VU4 Valve Unit eliminates 6 of the culprits and minimizes the number of pipe threads on most systems to 8, instead of 14 or more. For the 8 pipe threads that you will have left, AccuAir includes a special “anaerobic” liquid sealant that has proven unbeatable. AccuAir only uses D.O.T. (Department of Transportation) approved P.T.C. (Push to Connect) fittings and line, which is also essential for eliminating leaks. (Always make sure to cut your plastic line squarely with a sharp blade to avoid tearing the fitting’s o-ring upon insertion). NEVER USE DIAGONAL CUTTERS!
Q: I’ve heard of people using compressed Nitrogen or Helium instead of onboard air compressors. Can I do this with an AccuAir system?
A: Yes, with one massive disclaimer: YOU MUST USE A PRESSURE REGULATOR BETWEEN THE BOTTLE AND OUR SYSTEM. FAILURE TO DO SO WILL RESULT IN A MASSIVE EXPLOSION THAT WILL LIKELY CAUSE BODILY HARM. The pressure regulator must be set below 200 psi for the VU4 valves to operate. Some prefer to use compressed Nitrogen or Helium bottles usually filled at a welding supply shop because it is a silent source of system power that can last for quite a while depending on how frequently you operate your system. Yet, there are some inherent risks and drawbacks to going this route:
Compressed Nitrogen or Helium bottles are initially filled to 2,000 psi, which can easily become a dangerous projectile. Some states have deemed them illegal for this reason.
The cost of filling your bottle ads up, usually $20 or more per fill.
Bottles are usually large and heavy making them hard to handle and hard to fit in most vehicles.
If the bottle goes empty and you don’t have a backup compressor, it could leave you stranded.
If you are still convinced that compressed Nitrogen or Helium is what you want, please call to discuss the proper installation and hookup procedures.
LEVELING SYSTEM FAQ
Q: Why do I want a height sensor based control system instead of pressure based?
A: Pressure based systems have proven to be very inaccurate. First, typical pressure sensors have an accuracy of +/- 5 psi, which can result in as much as 1” in ride height on lightweight vehicles. Second, pressure sensors don’t account for changes in load. As your vehicle load increases, the vehicle drops, and your air spring pressure increases. A pressure based control system will reduce the pressure in the air springs back to the target pressures, which will further lower the vehicle. The e-Level System uses TruPositionTMheight sensors and will provide adjustment accuracies of better than 1/8” at the wheels as well as compensate for changing vehicle loads by adding whatever pressure is necessary to obtain the target vehicle height.
Q: I see some other systems have ride height sensors along with per air spring pressure sensors, claiming that this method prevents crossloading of air springs. Is this true?
A: No. First, the definition of crossweight also known as “wedge”; This is the comparison of the vehicle’s per wheel weight totals at diagonally opposite corners to the car's total weight. For the average street handling application, road-course, or slalom event, the goal is zero-wedge, or 50 percent crossweight, which results in equal response for both right and left hand turns. When the wedge is positive or negative, the vehicle is considered to be crossloaded. AccuAir has conducted extensive testing on corner weight scales with the e-Level system vs. the competition, (Read “Air on Scales”). The results proved that controlling the heights as accurately as the e-Level system does yields wedge repeatability of better than 1%, whereas the competition struggled to get within 10%. Not only does the use of per air spring pressure sensors not work, but it also increases the total cost of the system and adds to the number of potential leak points and parts that could eventually fail… leaving you stranded.
Q: What is so special about your RideMonitorTM Mode? Does your competition have anything similar?
A: AccuAir’s e-LevelTM System with RideMonitorTM Mode is the result of 3 years of development and provides flawless corrections while parked and driving. Extensive strategies have been developed to avoid unnecessary corrections by detecting transient driving scenarios like stopping, turning, and accelerating. This results in a vehicle that is always within height specification yielding improved ride quality and consistent handling characteristics.
The majority of the competition’s systems level once and then go to sleep, (This is actually how the AccuAir Gen I System operated). If you change the load in the vehicle, or initially level on an off-angle driveway you would have to remember to hit the button to re-level. Only a few have attempted semi-active leveling and the results were unsatisfactory (corrections at every stop and turn with the vehicle out of height specification the majority of the time while driving). The proprietary technology that makes the RideMonitorTM Mode so effective is currently patent pending and promises to hold its superiority in the marketplace for years to come.
Q: I see some other systems use valve-pulsing to work with fast-valves, does this work?
A: Yes it does work, but not without compromise. These systems cycle each of your valves as many as 20 times per adjustment reducing the life of the valves and significantly increasing the adjustment time. The e-Level System utilizes a Straight-to-HeightTM adjustment strategy and automatically learns the characteristics of your valves to perform accurately even with fast-valves. This strategy achieves the fastest adjustment times possible and maximizes the life of your valves. Because the e-Level system does all of this automatically, the need for user tuning and “valve pulse number adjustment” is completely eliminated.
Q: Many of your competitors have interfaces that display pressures and height indication bars. Why doesn’t yours?
A: There are a number of reasons:
Air spring pressure readings are absolutely irrelevant when it comes to setting the height of a vehicle because they vary with load and temperature, (two conditions that will be constantly changing on every vehicle). Most vehicles have unequally loaded corners due to offset fuel tanks and other components which can require as much as 15 psi differential between sides to get the vehicle level. We see no need to display these variations because they are simply confusing and unnecessary.
At first, height indication bars or graphs seem like a decent idea. Yet, most companies utilizing height bar displays have broken them into only 10 divisions. The e-LevelTM System’s resolution is so high that it breaks your total suspension motion into 1,024 divisions. We feel that displaying anything less than this would be misrepresenting the system’s accuracy, so we would have to use a decimal type display like “100.0%” of vehicle height. The problem with going this route is that any height display has to be based on the measurements taken from the ride height sensors, which are spanned during calibration based on the total suspension travel (which is usually not exactly equal from side to side due to geometric variations in the suspension system). The result would be that with the fender measurements equal from side to side the height display could read 49.2% on the left side and 52.2% on the right side even though the vehicle is actually level. This again leads us to the best method for saving a height; using a tape measure at each wheel opening on flat ground to set the vehicle level from side-to-side.
The bottom line is that the average customer simply wants to know “is the vehicle at my highest saved height, my driving height, or my lowest saved height?” As the user, you will know exactly where each of these heights is saved because you will have measured the ground to fender distances while saving them. The e-Level System guarantees that the vehicle is exactly where you saved it when the given position indicator is lit. This makes for the cleanest interface and overall simplest system to operate.
Q: Will the e-Level System work with other manufacturer’s solenoid valves?
A: Yes, our system will work with any 12-volt solenoid valves on the market. The benefit to using the AccuAir VU4 Valves with the e-Level system is the ease of wiring because the harness is plug’n’play for this case. If you are using other manufacturer’s valves, you will have to make sure to connect the solenoid drive wires from the e-Level in the correct orientation to your valves. (We do offer adapter harnesses for some other manufacturer’s valves, but in all cases our harnesses are color coded for easy hookup.