Suspension includes the springs, shocks, and arms that move up and down to allow your car to absorb bumps and imperfections on the road. A stock suspension system is designed with a focus more on comfort than aboslute handling ability. A stock car rarely is designed to perofrm as well as possible. They donn't respond well to driver input, and when pushed to the limit, stock suspension tends to overload one tire. Many things can be upgraded on the suspension system, infact almost all components can usually be replaced for stiffer, lighter, stronger, more adjustable units. Most suspension parts are interrelated, so many will have the same benifts, the parts are listed in order of how they should be upgraded.

Springs:

I guess you could say this is where it all begins. With no spring, you have no real ability to extend or contract your wheel. Most stock cars have very soft springs, this is to offer a smooth ride and long wheel travel. On a sports car, and even more so on a race car, you can raise spring stiffness, which inturn lesses your suspension travel. This is good for high performance driving because, when using soft springs, weight transfer is drastic and unpredictable. Lateral acceleration is lower than it should be due to overloading the outside tires, and quick changes of direction can cause loss of control due to excessive weight transfer. Stiffer springs will make your car bounce more on a rough road, infact stock suspension may handle better than a race inspired coil-over system on some rough roads, but that is because they were designed for decently smooth roads, and smooth roads is where they perform their best. Stiffer springs also lower your cars stance, since there is less suspension travel, you can get away with less fender gap without rubbing the fenders on full compression. This helps lower the centre of gravity and again improve handling. Stiffer springs will also help in braking as there wont be as much weight transfered to the front of the car, however acceleration on a rear wheel drive car may be decreased since weight transfered over the rear wheels will be less. Progressive springs are available that combine soft street characteristics with stiff short travel high performance characteristics. These springs are good for the street, however you dont have the same nimbleness as you do with a static rate sports or race spring, and is not that good for circuit use, where high speed stability is required. Cheap spring kits lower your car a set amount with a set spring rate. High end systems allow you to alter the cars ride height independantly at each wheel, as well as adjust fully extended spring tension. These systems are usually coilovers with shocks built in, such systems are used on the project GS (Tein) and 240sx (JIC).

Shocks:

Shocks should be upgraded at the same time as springs, for ease of installation, and performance. Springs alone can be a dangerous modification, since stock shocks are much too weak. Shock absorbers are just that, absorbers of upward and downward shock onto the chassis from the wheel. If you had no shocks, the car would bounce forever, because little imperfections in the road would keep the springs bouncing forever. Shocks are designed to smooth out the job of the spring, and for this reason the shock needs to be well matched with the spring. The shock absorber absorbs two types of motion, bound, and rebound. bound or compression, is when the wheel is moving towards the chassis, and rebound is when the wheel moves away from the chassis. the shock works to keep the travel smooth in both directions. Stock shocks are too soft, when used with stiff sports or racing springs, the car bounces too much. Stiffer springs are put in place to keep the car more stable and to perform better, not bounce, and grip the road. High end damper systems allow for stiffness adjustment of the shock.

Sway Bars:

Sway bars are bars that run from one end of the car to the other, linked to the chassis. The term "fully independant suspension" starts to loose its meaning here. The sway bars connect to the chassis and other wheel to lessen suspension travel and reduce "body roll" or "sway." This helps for stability in cornering and reduces weight transfer, simaler to springs. Stock sway bars are usually too small, with the rear being esspecially too small. A small (i.e. soft) rear bar will cause more understeer, which is prefered for OEM cars, since understeer is more predictable than oversteer. Aftermarket bars usually cause a more neutral handling feel and totally remove body roll from the car. Remember that the stiffer your sways, the more you are linking your suspension, with a short stroke suspension design and stiff sways you may experiance the inside rear tire lifting off the ground in cornering, which will burn out your differential pretty quick, or in the case of an open diff, slow you right down.

Bushings:

Stock bushings are made of rubber, cheap and soft. Good at wearing out fast and absorbing vibrations. On a sports or race car, you dont want to absorb vibrations, because absorbing vibrations causings mush and slack in the suspension. Esspecially on old cars where the bushings have totally worn out and possible even ripped, upgrading the bushings will give your car that like new feeling again, and will stiffen things right up. Actual performance numbers wont increase much, however, feeling is important too.

Arms / Rods:

The last step in suspension tuning is the hard arms and rods, with no bushings at all, direct feel. This is hardcore stuff. Causes a harsh ride (like a go-kart), and lets you feel EVERYTHING on the road. Also gives you adjustability of stuff like camber, caster, and toe. These peices are usually also lighter than stock, and your car will be extreamly nimble after the installation of these components.