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An Inside Look at Vehicle Suspension Systems

An Inside Look at Vehicle Suspension Systems

By Jeff Youngs, February 24, 2012
Late-model passenger vehicles are very sophisticated machines. Mechanically speaking, there are countless different systems that work together as your car, truck, SUV or crossover drives down the road. Tasked with delivering a stable and comfortable ride-while maintaining controllable handling and braking-is the vehicle's suspension system. Like most other components on a vehicle, manufacturers have taken many different approaches when it comes to suspension design. Luxury cars are engineered for a comfortable ride, while sports cars need to corner at high speed. Trucks, on the other hand, need to carry heavy loads and may travel off the pavement.

In general terms, there are two basic types of suspension: rigid axle and independent suspension.

2009 Jeep WranglerRigid Axle
Rigid axle (also referred to as "solid axle" or "live axle") suspension was the first mass-produced design. Just as the name infers, the rigid axle suspension uses a solid beam to connect opposing wheels. When a wheel on one side hits a bump or moves, the wheel on the other side is negatively affected, decreasing ride quality. While this is an obvious drawback, rigid axle suspension is inexpensive to manufacture, offers lots of wheel travel (which benefits off-road travel), and it can be designed to carry very heavy loads, making it popular for trucks. The Jeep Wrangler uses a rigid axle on both the front and rear, while the Ford F-150 pickup and Nissan Titan pickup use a rigid axle only on the rear of the vehicle.

2008 Honda RidgelineIndependent Suspension
Independent suspension is much more prevalent today. As the name implies, each wheel moves independently over the road surface, isolating the remaining wheels from the impact. Independent suspension is more complex, but offers a much improved ride compared to rigid axles. The drawbacks include complexity, increased cost, reduced wheel travel, and reduced load capacity. The two most common types of independent suspension are MacPherson struts and double-wishbone suspension. Independent suspension is found on most sedans and sports cars today including the Ford Fusion, Lexus LS, and the Subaru Impreza WRX. In a unique move, the Honda Ridgeline pickup truck also uses an independent suspension.

Whether rigid axle or independent, suspension engineers have a variety of tools at their disposal when it comes down to the details. These different components-including the shock absorbers, sway bars (also called anti-roll bars), and springs-are combined to tune the ride specifically for each model. Many new vehicles take this one step further by integrating sophisticated electronics into their suspension designs.

Springs
Springs are mechanical devices (made of metal or plastic) that are designed to provide a vehicle with a smooth ride by compressing or bending under pressure-and immediately recovering their shape afterwards. The most common automotive applications include leaf springs (often used on a rigid axle), torsion bars and coil springs (both used for independent suspension). Some newer vehicles utilize "air suspension" with air-filled bladders replacing the springs. Air can be added or subtracted-raising or lowering the vehicle-either automatically or by a switch mounted in the passenger compartment.

2010 Audi R8Shock Absorbers
Shock absorbers work in conjunction with the springs by damping, or reducing, harshness as they absorb the energy from road impacts and sudden vehicle movements (a "strut" is a type of shock absorber that integrates the shock with suspension components). The most common shock design utilizes a metal tube filled with air or oil-or a combination of the two. More recently, automakers have developed sophisticated shock absorbers filled with a special liquid that instantly reacts to an electrical current-using magnetic properties and called magnetorheological shocks-controlled by a computer that is able to alter suspension settings within milliseconds based on driving and road conditions. For example, vehicles such as the Audi R8, Chevrolet Corvette and the Ferrari 599 utilize this technology.

2009 Lexus LXSway Bars
Sway bars ("stabilizer bars" and "anti-roll bars") are designed to limit body roll by connecting the left and right side of the vehicle together mechanically with a simple torsion spring-essentially nothing more than a steel bar. The thickness of the bar determines how much the body is allowed to roll, and how the vehicle handles in corners. Some vehicles don't have sway bars, while other high-end vehicles are fitted with electrically controlled sway bars that can vary their actions automatically. These include the Lexus LX 570 and BMW 550i, among others.

In the future, suspension designers will work with advanced materials that are able to do the same work as today's components, but are much lighter. A lighter weight to the suspension components equates to a smoother ride, improved handling, faster acceleration, quicker braking, and increased fuel economy. In addition, low-cost electronic controls will be introduced that will allow suspensions to automatically adapt themselves to the driving conditions, meaning nearly all vehicles in the future may be able to offer a soft ride on bumpy roads yet deliver sporty and controlled driving dynamics when required or desired.


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