Consider you have 2 springs having different spring rates: One with 345 g/mm and the other with 480 g/mm. So what does it mean?
It means the 1st spring will compress 1 mm if you put a load of 345 grams, while the 2nd one will not. The 2nd one will need a 480 g. load to compress 1 mm. According to this, we can say that the 2nd spring is harder than the 1st one, or we can state that:
Springs that have a low Spring Rate are soft, while springs that have a high Spring Rate are stiffer.
If there are 2 different values listed, it means that the spring starts at one rate, and ends at another rate under full compression.
For example: a 10lb to 25lb progressive spring will need 10lb to compress it the first inch, then 13lb the next inch, and so on, until the end of the travel; it will take 25lb to compress it the last inch. The benefit of this is that the spring can be soft enough at the start of the travel to offer a soft ride yet be stiff enough at the end of the travel to performance well during hard braking and turning.
What Affects the Spring Rate?
There are 3 things that affect the spring rate:
1. Diameter of the wire: Diameter of the wire itself affects the spring rate because when diameter of the wire increases it gets stronger, meaning a wire which is harder to compress. So, if we know that a wire becomes harder when its diameter increases, we can say that:
When wire diameter increases, spring rate increases.
2. Diameter of the spring: That is in fact 'the mean diameter of the spring', achieved by subtracting the diameter of the wire from diameter of the spring:
The overall outside diameter of the spring (mm) - diameter of the wire (mm)
When diameter of the suspension spring increases, the spring rate decreases.
3. Number of Active Coils (length / height of the coil spring): Determination of the active coil number varies according to spring design. Total coil number -2 for springs with both ends closed. Count the total coils -1 for springs with one end closed and one end open.
As the number of active coil decrease, the spring rate increases.
Normal Springs has a fixed spring rate.
Step Linear Springs are springs which have 2 different spring rates.
Progressive Springs have a variable spring rate.
Step Linear Springs (2 Step Linear Springs)
These are springs that have a 2 different spring rate.
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. (HyperPro website)
3. 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.
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 Eibach 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.
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:
-Easier to produce and can be made to lower a car beyond the point of progressive springs.
-Easy to work with, because spring rate never changes, allowing quick chassis setup
-Cheaper than progressive springs, allowing most race teams to use several different sets depending on track conditions
"b springs are progressive c springs are linear.
Linear springs...no matter how hard you compress them, they will always have the same resistance
Progressive springs...the harder you compress them, the more resistive they become...thats why the progressive springs have a 425-530 lb/in rating...first inch they are 425 in/lb and then get more resistive after that
The reason the progressive springs are good for stock struts is because they do part of the dampining. Linear springs do not do any of the dampening.