and the nail in the coffin:

Springs
Springs are very important in determining the responsiveness of your car. All weight above the springs is called "sprung weight." While this has an effect on drag, the main concern is "unsprung weight." Unsprung weight is basically what the engine is trying to move, and what the shocks are trying to dampen. A generally accepted ratio is adding 1 lb. of unsprung weight is like adding 10 lbs. of sprung weight. Consider that before you buy your bling bling dub-deuces.

Besides supporting the weight of the cabin, springs also affect how the weight in the car is distributed. For those of you with upgraded springs, you might have noticed the car doesn’t rock back as far when launching. Springs push against whatever force is applied to it, so when your car leans in a direction, the springs counteract that. The stiffer the spring, the more it prevents weight transfer. This is why racecars use stiff spring rates. On uneven terrain, though, the spring might not react quickly enough to keep the wheel in contact with the ground.

There are two types of spring designs: progressive and linear. Progressive springs are designed for comfort without giving up too much in the way of handling. They are coiled in a way that provides a low spring rate when uncompressed, and stiffens the farther the spring is compressed. This means you don’t have a stiff ride, but can still have some fun. They are inferior springs for real racing. Linear springs have a set spring rate that does not change. This can be soft for a luxurious ride, or ultra stiff for precise handling, or anywhere in-between. Linear springs provide a much more predictable feel.

Shocks
Ever see a car with cut springs that just bounces as it is going down the road? These people have blown out their shocks. Shocks act as a damping force to keep the springs from constantly compressing and decompressing (that is why they are sometimes referred to as dampers). The more force applied to the shock, the stiffer it becomes. If you ever install shocks, try compressing the shock on the ground, slowly. It smoothly compresses without much trouble. Now suddenly throw your weight on it. Nothing will happen until you relax some of the pressure. This is how a shock stabilizes the weight of the car.

A few factors go into choosing a shock. First of all, the travel of the cylinder. Shocks like to function towards the middle of their compression distance. That is why some shocks aren't warrantied, or don't perform well past a certain drop. When the shock is forced to perform at full extension or compression, it won’t be able to dampen properly and will blow. The other factor is the valve rate. Shocks have lots of little valves in the body that use a gas or liquid to create compression. As stated earlier, the faster the compression the more pressure the gas or liquid creates. However, if the valves aren't sized correctly, they will blow. This is why you avoid lower end shocks if going with a stiffer race-type spring.


True coilovers and sleeves
There are two different suspension setups that are referred to as coilovers. The first is a true coilover system. These are designed for the hardcore enthusiast and racer. They comprise of an adjustable height spring with a custom valved shock. The shock will always be designed to work perfectly with the spring, so blowing them isn't a concern. They are almost fully adjustable, so they have the versatility to work with any type of racing. The downside is the high price tag. These systems start at $750 and can range up to $2000 and more.

The other choice is technically a coilover sleeve. This unit is only a spring mounted to hardware that allows a height adjustment. Most are low quality and come with cheap springs. They can be found for low prices and the adjustability is a plus for many people. Some of the better brands are Ground Control and Skunk 2. The Ground Controls can be purchased with a custom spring rate, which makes them a favorite with autocrossers.