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 FAQ: Spring rates for everyone 
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Post FAQ: Spring rates for everyone
What is Spring Rate?

Basically, Spring Rate is the amount of weight needed to compress a spring a certain . Springs are rated in LB/in (in metric system kg/mm), or specifically, how many pounds of weight are required to depress the spring by one inch. To convert LB/in to kg/mm international, you must divide divide figure by 56.

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 spring increases, the spring rate decreases.

3. Number of Active Coils (length/height of the spring): Determination of the number of active coils varies according to spring design. Count the total coils minus two for springs with both ends closed. Count the total coils minus one for springs with one end closed and one end open.

As the number of active coils decreases, 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.

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December 21 2004, 6:51 PM
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