Progressive Springs (Rising Rate Springs, Progressive Rate Springs, Progressive Wound Springs)
In progressive springs each coil is spaced differently and have a variable spring rate. When free, it is easy to compress progressive springs for first centimeters. As you apply more forces, coil on a progressive spring come closer. After a certain point, coil at the top 1/4 of progressive springs begin to touch each other and finally become inactive or dead, and that makes the spring stiffer. Apply more forces to a progressive spring then it becomes stiffer because as the number of active coils in a spring decreases, the spring rate increases. So, progressive springs may both be sensitive to very small bumps on the road, while giving the stiffness you need during hard braking and turning.
Step Linear Springs (2 Step Linear Springs)
In a two-step linear spring, about half the coils have shorter spacing. As the spring compresses, the coils move closer. At a certain point, the shorter spaced coils touch, effectively eliminating them from the spring. You then have a spring comprised of only the longer coils. This "second-step" spring will be much stiffer than the whole spring (the more coils, the easier it is to compress the spring). The result is that you have one set of handling characteristics before the shorter coils touch and then you have another, completely different level of response after they touch.
Linear springs
are more often used in drag racing, road racing, track and races that require a "high spring rate", in which a constant spring rate is more important than a smooth ride. They are still popular because they are:-
1. Easier to produce and can be made to lower a car beyond the point of progressive springs.
2. Easy to work with, because spring rate never changes, allowing quick chassis setup
3. Cheaper than progressive springs, allowing most race teams to use several different sets depending on track conditions
Each spring design has its own market.
Progressive springs are likely "all-in one" solutions. Progressive springs are often used on performance aftermarket kits like KW or Weitec or others, and they are good for daily performance street driving. They help you achieve the highest performance when driving hard, while providing a smooth, comfortable drive the rest of the time.
I don't have any photos of Eibach or H & R 's but they are both progressive
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KW and Weitech suspension kits - T4 and T5 accessories