Tuesday, February 26, 2013

Air vs. Static: Battle of the Springs

Aftermarket Suspension Systems Explained

Compiled by Marcel Venable

There’s an ongoing debate about which suspension system is the better choice for classic or late model trucks. Similar debates or conspiracy theories also exist, including Chevy vs. Ford, Coke vs. Pepsi, and if the U.S. really put a man on the moon. Nevertheless, we wanted to get to the bottom of the suspension dilemma, so we sought opinions from manufacturers of modern day aftermarket suspensions. Let’s start with the basics.

Most customized trucks are the product of an independent front suspension system that includes some type of control-arm-over-spring combination. Yes, there are other types, like I-beam and torsion bar styles, but most aftermarket performance-based systems manufactured today are targeted to enhance the control-arm-over-spring units found in most trucks.

Starting from that foundation, let’s focus on the modern era of GM-based trucks beginning with the 1967-72 model to the current model GM truck platform. Why GM? Well it’s simple, for most of its 40-year span the principles of this style have remained generally the same. Plus, this type of suspension is close to that of most performance automobiles; many of the manufacturers of these units share what they’ve learned from vehicle to vehicle. Sure, most of the theory is correct, however just because it walks, talks and looks like a duck doesn’t always mean it’s a duck. First you must look at the components and their functions. Understanding how this style works will help you form a better conclusion based on what or how you what to drive your truck.

The IFS or independent front suspension theory is simple, both wheels travel at a different rate based on road conditions and on a vertical and/or lateral force. A coil spring is located under the frame on both sides that carries the weight of the vehicle while maintaining the ride height, and to an extent, reflects vertical and lateral force. A shock absorber assists the coil spring to control vertical and lateral forces. Steering or control of the vehicle is guided by the other components, such as the control arms, spindles and the steering linkage. These are partnered with other items, such as an anti-sway bar and the shock absorbers.  

We all know that GM setup its truck suspension to haul heavy loads and fit an oversized tire with a ton of sidewall to handle more weight than automobiles. Simply put, trucks are naturally handicapped with a higher center of gravity, an undesirable stance and huge amounts of body roll or sway. So how do you change a truck into a ‘Vette? It’s geometry, my friends, geometry

First, it’s necessary to change the ride height, which will alter the center of gravity and reduce the exchange of weight transferred laterally while cornering. There are many ways of doing this and is where the debate begins.

Option One: Lowered Coil Springs and Spindles

These components are the simplest as well as the most affordable way to change ride height. Simply install a shorter coil spring along with a corrected spindle. Changing just one component won’t ensure the best handling and drivability, and as a matter of fact, will create all kinds of problems with wheel and tire alignment, making the vehicle almost impossible to drive at highway speeds. It’s a good idea when changing coil spring height to include some type of partner component, like a spindle to maintain proper geometry, if you plan to make a drastic ride height change. 

So what are some of the effects from just changing only one of the components? An increase in negative camber is the first that comes to mind. Too much is never a good thing. Having too much negative camber can cause horrible tire wear. The fix is to bundle the items together creating a balanced system that will help maintain proper geometry at a lowered ride height. Another method is changing both the upper and lower control arms. They’ve been engineered to maintain the factory geometry of the coil spring and spindle geometry, so changing them will alter a truck’s ride height. For anything more than a 2-inch drop up front, shorter shocks are a must. Many companies offer specific shocks tailor made for lowered trucks.

Option Two: Airbags
First, the term “airbag” isn’t the proper term for this component. As a matter of fact, an airbag is really a pnuematic spring. They were developed to allow drivers to change spring rates using compressed air, thereby adjusting a vehicle’s ride height based on heavier loads. Air springs are common equipment on most tractor-trailers, buses, trains and even luxury automobiles. In recent years, customizers have co-opted their use on their own projects.

While most of us love the look of a truck hugging the pavement, there are trade-offs to consider. Unfortunately, a truck that’s extremely low will have very little suspension travel, so to get any kind of ground clearance you have to raise the truck to a safe ride height. The same person might install an air suspension as a way to clear large diameter tire and wheel combos. To do this they have to overinflate the springs to avoid rubbing the tires on the fenders, resulting in a harsher ride. Finding a balance is paramount, and mounting locations can be changed to help gain more lift and/or better ride at lower levels.

So does this mean they’re only good for hauling weight? No, as a matter of fact, when the proper components are matched, air springs offer the user exceptional handling and stability, regardless of load. This means that you can maintain the same ride height no matter how much weight is added. How? Because the operator has the ability to add air pressure to the ‘bag, which will change the spring weight rating based on air pressure, thereby creating a progressive spring. In most cases, the driver can control air pressure through the use of an in-cab valve controller. Some manufacturer’s systems can be preset, and even electronically monitored via computer with a leveling system. When paired with a corrected geometry system (control arms and ‘bag mounts), you can experience close to a perfect balance between ride quality and handling characteristics. Lowered shocks are a must for a proper ride because the airbag only acts as a spring replacement; a shock is still needed to control rebound. The proper combination can result in a low ride that rivals any luxury car.

If space is limited, the application may call for a ShockWave, which is simply a combination of an air spring and a shock absorber. The advantages are easier mounting, more tire clearance, a better working angle for the shock and the air spring, as well as the inclusion of a high quality billet adjustable racing shock.

Option Three: Coil-overs

A pair of coil-over shocks shares many similarities with the ShockWave system. It’s a combination of an adjustable shock absorber, surrounded by a metal-wound coil spring. One of the advantages of installing a pair of coil-overs has a lot to do with space, just like it does with the Shock Waves; however, they send more positive feedback to the driver at higher speed.

They are adjustable, but not on the fly like an air spring. Based on the vehicle’s ride height and/or suspension travel, the operator can choose a spring based on the coil spring’s weight rating. The stiffer the spring the more vertical and lateral resistance is created to control more of the force that’s generated by vehicle weight during high speed cornering. This makes them ideal for use in a racing applications, but does this mean that’s all they’re good for? No, but knowledge is power, so understanding more about your truck’s suspension makes a huge difference. For example, having an idea of how much weight is being distributed on all four tires will allow you to get closer to choosing the proper coil springs. This is what is referred to as “corner weight,” and it’s vital to making the proper selection of coil spring. Coil-overs allow some ride height adjustability, but they’re limited to the shock’s travel parameters. A good rule of thumb is to pair coil-overs with the correct suspension components, like corrected control arms.

What’s the verdict? It’s difficult to say for sure. Only you can answer that question because you’re the one who will be driving your own truck. Be sure to weigh all of the options before you make your decision.

We will leave you with this advice, though, to crush any myths. Maintaining proper geometry is the right way to set up your truck’s suspension no matter which spring you choose to install. Also, airbags and coil-overs aren’t just for trailer queens and race cars. When paired with the proper components, they’ll make your truck handle just as well if not better than most sports cars for a fraction of the cost.






Cando Specialties

Chris Alston Chassisworks

DJM Suspension



KP Components

McGaughy’s Suspension

No Limit Engineering


Romic Billet Shocks

Slam Specialties


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  7. The suspension on my truck hasn't exactly been great. My truck's center of gravity used to be really great, but now I can feel that the weight has shifted to a really weird spot. Should I replace a few of the coil springs or spindles to properly adjust the center of gravity in my truck? It feels really weird driving around when my truck feels so off center, so I really want to have it re-centered soon.