What is Spring Rate?

Spring rate refers to the amount of force necessary to compress the spring. It is usually measured in pounds per inch or kilograms per centimeter.

An example is a linear spring rate of 300 pounds per inch. For every inch the spring is compressed, it exerts 300 pounds (lbs). A typically progressive non-linear spring rate is one that the force applied increases exponentially. For instance, the first inch exerts 300 pounds force, the second inch exerts an additional 350 pounds (for a total of 650 pounds), and the third inch exerts another 400 pounds (for a total of 1050 pounds). This contrasts with the linear spring exampled above, which if compressed to three inches, would render only a total amount of 900 pounds.

In automobiles, a system of strings, shock absorbers and linkages that connects a vehicle to its wheels is called suspension. This system serves a dual purpose which contributes to the car’s handling and braking for active safety, driving pleasure, and keeping occupants comfortable from road noise, vibrations and bumps.

Spring rate refers to the stiffness of the spring that determines how soft or stiff a vehicle will ride. Vehicles which carry heavy loads like trucks are typically built with heavier and bigger springs. This compensates for the additional weight which could collapse the suspension to the bottom of its travel or stroke. Bigger and heavier springs are commonly used in high-performance applications where the suspension experiences heavy loading in the corners. Spring rate is frequently a bargain between drive comfort and better handling.

The spring rate of a coil spring may be calculated by a simple algebraic equation manually or programmatically, or it may be measured in a spring testing machine. Spring rate (K) is equal to wire diameter (d) to the fourth power times spring modulus 12.000.000 all divided by eight times the number of active wraps (N) times diameter of the coil (D) cubed.

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