We rely on a car's suspension to keep us from jolting up, down, left and right as we drive along the road. In the most basic form, the suspension is made of springs and dampers: either shock absorbers or struts. When your tires hit a bump, the springs compress and absorb the energy. Naturally, the springs' loaded energy makes them expand again after the bump. The springs want to continue the bouncing up and down in this fashion, but the shock absorbers constrict this movement. This is why, in an older car where the shocks need to be replaced, you will feel the waves of a bump long after passing over it. Without the proper combination of springs and dampers, your car would react violently and sacrifice control over even the slightest bump.
Types of Springs
The three most commonly-used springs in automobiles are coil springs, leaf springs and torsion bars. Coil springs are just as their name indicates, a twisted metal coil. The coil is either mounted separately from the damper or integrated (as with coilovers). Leaf springs are layered metal planks (leaves) that support the axle in the centre and attach to either the body or shackles. This type of spring can be found primarily in trucks, vans and SUVs, but most modern cars are now equipped with coil springs. Torsion bars, which have nearly disappeared from use in modern times, were once widely used in the auto industry. The bars are mounted from the chassis to an axle or arm that moves with the bumps in the road. As the force of movement in these areas creates torque on the bars, the metal will resist twisting and bring the system back to its original place. Unless you are driving a Porsche 911 or an original VW Beetle, you probably aren't in the market for a new torsion bar.
Shocks vs Struts
The most commonly misused terms associated with suspension are shocks and struts because people tend to use them interchangeably. Don't get it confused. Although they look similar and serve a similar purpose, the two parts are very different. Shocks, or shock absorbers, only act as dampers. The hub carrier is held in place with multiple arms, and the location of the shock does not change the location of the hub carrier. Struts, however, take the roles of dampers and upper control arms. They are mounted to the hub carrier and turn with the wheels.
Coilovers combine coils and dampers into one part. They are quite literally coils seated over dampers. Depending on your needs, you may find coilovers that are adjustable in multiple areas. The spring plate can be moved to make the springs looser or stiffer, the damper valve can be adjusted to change the response of the damper and the ride height can be adjusted on some coilovers. More cars use coilovers now than ever before, but many still use separate damper and spring set ups in the rear.
The Whole Package
For a suspension system to work properly, each piece must cooperate precisely with the others. If you're only replacing your dampers to get a smoother ride, purchase the exact fit for your make and model. If you are installing new suspension to change ride height or for better performance, be sure to purchase matching parts and do the swap at once. A common mistake is to mix and match shock and spring brands, resulting in springs that are too stiff for the shocks and vice versa. This happens more often when installing a new suspension system to lower the vehicle, and it is why coilovers are preferred when lowering a car. When making the change from stock suspension to a different set up, check out the conversion kits, lift kits or lowering kits available for your car. These will come with all the appropriate fittings to ensure your new suspension fits properly, and you can drive safely.
The whole point of upgrading your suspension is to minimise the vibrations and movement from the road. Even with new shocks and springs or struts, there may be areas that transfer noise and vibration to the body of the car. The factory-installed rubber bushings are cost efficient, but they can crack and wear, causing areas of rotation between suspension components. Replace these bushings with new polyurethane or polygraphite bushings to keep everything in place and reduce the effects of the driving surface on your comfortable ride.
The Right Suspension For The Ride
Before you commit to any one suspension set up in particular, it is important to look at how you'll be using it. Daily driving on paved roads, for example, puts far less wear on your suspension than off roading, autocross, racing or rallying. Consider the importance of braking, turning at high speeds, overcoming bumps and driving on inclines. Because every movement of your vehicle depends on its suspension to maintain control, you must purchase parts that are capable of doing the job well. Always find a direct fit for your car and purchase from a reputable seller. If you have any doubts, contact the seller first for advice before you waste time and money on a failed project.