Let's say your buddy builds a '48 Ford with a Camaro front subframe and S-10 leaves in the rear. It rides great! You want to build one the same way, only yours will be powered by a big-block. It now sits too low and rides like hell. Now you can start the research all over to find a set of coils and leaves that will be appropriate for your vehicle.
With an air suspension it is a matter of adjusting the air pressure to accommodate the extra weight in the front and less weight in the rear. The added benefit is that when you add a bit of a load for that trip to the Supernationals, all it takes is an extra squirt of air to level the truck and restore the ride quality.
CT:What do you suggest for general air suspension guidelines?
BV:There are a few things to be aware of when building any suspension, especially an air suspension:
The vehicle needs to be mocked up at your intended ride height. This ride height needs to reflect proper ground clearance (at least 4 1/2 inches) and adequate suspension travel (at least 3-inches compression and 2 inches in rebound). After that, start looking for a place to install the air springs at their intended design height. This is very important! If you have an air spring that is intended to ride at 9-inches tall and you try to make it run at 7-inches tall, the best ride quality will make the vehicle ride 2-inches taller than you want. If you deflate that air spring to that 7-inch height to make the truck sit right, the ride quality will suffer. Any competent air spring supplier will be able to give you the compressed, ride height and extended dimensions of their air springs.
A lot of customers want to "lay the truck on the ground." Don't do it. You must have at least an inch or so of ground clearance when the air system is fully deflated. Remember that you need at least 4 1/2 inches of ground clearance at ride height to be able to negotiate speed bumps and other road obstacles safely. I don't care what anyone says, it is not cool to scrape!
Driveshaft And Ball Joint Travel
Ball joints will only travel so far before they bind. The driveshaft will go only so far into the transmission tunnel before it hits. It is your job to find these limits and take them into account.
Air Spring Clearance
The only rule here is that the air spring must never rub on anything at any time. Period!
It requires considerable thought and planning to properly satisfy all of these details. The nice thing about an air suspension is that you can inflate and deflate the vehicle through its full range of travel to check out all of these parameters. A conventional suspension makes it much tougher to accomplish this.
CT: What about the compressor system?
BV: After you have properly designed and installed your air ride suspension, you will need a source of compressed air and a way to control it. While it is possible, at least in theory, to use an inflation valve or even a bottle of compressed air to inflate your suspension, the most efficient method is an on-board compressor with a reservoir tank and a control valve. It is with the compressor system that you can upgrade, customize, economize, or thoroughly overkill without drastic compromise. If you are doing a simple supplemental air spring over a leaf spring, then an inflation valve may be enough. Any stand-alone air suspension really needs an on-board compressor and control system. Here is why: Ride quality tuning is done in very small air pressure increments. Because the air springs are quite small in volume, it is very hard to inflate or deflate in small enough increments to zero in on a great ride quality. In addition to that, when you add load in the form of fuel, people, or uggage, you have to go looking for an air hose! You can quickly see how convenient an on-board system can be.