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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.

This information was forund on the net.