Some Suspension Basics

[ProtegeSTS]

COIL SPRING
Since almost every car uses coil springs these days, you don't need to know about anything else. A coil spring is exactly that, a coil of wire that takes a certain amount of energy to compress and expand. The energy it takes to compress the spring is what determines the srping rate, which is usually described in lbs/in or in kg/mm. A spring that is decribed as having a rate of 300 lbs/in takes 300 pounds of force to compress it 1 inch. <p>LINEAR VS. PROGRESSIVE RATE COIL SPRINGS
A linear spring has a straight compression rating, meaning that for our earlier example it would take 300 lbs of force to compress the spring every inch throughout it's total travel. Say the car weighs 300 lbs at one corner, well the spring at that corner would be compressed one inch once installed. For each additional 300 lbs of pressure put on the spring, it would compress an aditional inch until it reaches minimum height. If the spring is termed progressive rate however, this rate changes as the spring is compressed. Many springs are progressive rate because it allows the suspension to be softer initially (making ride quality better) but stiffening up as the amount the spring is compressed increases. This allows you to make the spring fairly soft at smaller compression while making it stiff enough at bigger compression amounts to accurately control wheel & suspension movement when you are hauling *** . Progessive springs usually allow the car to ride & handle better if they are properly designed, but the added complexity to designing and making them work properly also increases the possibility of screwing things up. For these reasons linear springs are often still used for our cars, but if you can find good progressive rate springs from a reputable manufacturer they will enhance both ride quality and handling. <p>SHOCK ABSORBER
This is what controls spring movement. What is almost always used on our cars are mono-tube hydrolic shocks, so you don't need to know about anything else. A shock absorber's job is to absorb shock (duh!), which means that it dissipates spring energy. Hydrolic shocks do this by moving a small piston with orifices in it through a viscous oil, providing the energy damping needed to control spring movement. The size of the orifices determines the resistance to movement the shock will have, and adjustable shocks have adjustable sized orifices to offer a range of resistance to motion. Since a car's coil spring can be likened to a big slinky, you can imagine that the same way a slinky bounces off one step and jumps to another, where it compresses again and then jumps away once more. A spring will do this just the same, causing the suspension to compress & rebound over and over again after hitting a single bump. The primary job of the shock absorber is to prevent this cycle, and if it's properly matched to the spring's rate it will only allow this to happen once. This is what keeps the tire in good contact with the ground, so you can imagine the importance of getting the shock stiffness right for your springs. The secondary job of the shock is to add some resistance to motion in the suspension, much like the spring does. There's no need to get deep into that yet, just know the shock has an effect on both ride quality and performance. <p>ADJUSTABLE SHOCK ABSORBER
Adjustable shocks allow you to change their stiffness. Now that you know how important it is to match the shock settings to the spring in order to keep the tire in good contact with the ground, you can also understand how it's control over the spring movement will affect ride quality. Since the shock absorber has some level of control over how quickly the suspension can be compressed (because it adds additional resistance to the whole system), you can imagine that making the shock stiffer will have the same overall effect on ride quality as stiffening the spring. There are two main types of adjustable shocks: those that adjust stiffness of the rebound stroke only and those that adjust stiffness on both compression and rebound strokes. It's not important to go over the different types of desgins here, but know that most shocks either only adjust rebound stiffness (called single-adjustable shocks) or they adjust both compression & rebound at the same time (called double-adjustable shocks). This means that there is no way to adjust the bias between compression & rebound stiffness on double-adjustables, which is of principle design concern to shock manufacturers because it's so easy to get the bias wrong. There are indepently double-adjustable shocks which allow you to change this bias, but I wouldn't recommend them for the average enthusiast. You will probably just end up making the suspension damping worse than it was stock. Recommendations here are usually to get the double adjustable shocks that control both compression & rebound (but not independently), and that's probably the best idea for the average enthusiast. <p>SWAY BAR
Torsion bar mounted rigidly to the chassis and both side of the suspension (per axle) which alters roll resistance primarily without effecting static spring rates or or suspension stiffness.<p>[ January 17, 2003: Message edited by: ProtegeSTS ]</p>