How to design Coilover shock absorber’s spring?

In a coilover shock absorber, a spring act as an energy storing device. The spring affects the performance of the vehicle. Hence need to be designed carefully according to the required vehicle performance. A compression spring is one such type which is simple in geometry and commonly used in a coilover shock absorber. A spring constant defines the stiffness of a spring and needs to be chosen or calculated based on defined suspension geometry and ride frequency.

Now let’s get into the calculations,

Where,

K – spring stiffness

G – modulus of rigidity

d – wire diameter

D = Outer spring diameter – d

n – number of free coils

Using the above formula and with the known value of spring constant (K), modulus of rigidity (G), and inner spring diameter, one can easily iterate the wire diameter and number of free coils (n) . Based on this parameter, a spring can be manufactured. There should be consideration of required compression in the spring while choosing the number of free coils. Because a higher number of coils may result in less compression length.  

ASTM 228 also known as music wire is one of the toughest and most widely used materials for making springs. It has a high tensile strength along with excellent fatigue life. ASTM 228’s modulus of rigidity (G) is 11.6 x 103 ksi and can be used for calculations.

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