Coil springs

The load-carrying ability of a coil spring depends on the wire diameter, the overall spring diameter, its shape, and the spacing of the coils. Coil springs can look alike but give very different load ratings, which are often color coded for identification.

Coil springs are used on the front suspension of most modern light vehicles, and in many cases, they have replaced leaf springs in the rear suspension.

A coil spring is made from a single length of special wire, which is heated and wound on a former, to produce the required shape.

The load-carrying ability of the spring depends on the diameter of the wire, the overall diameter of the spring, its shape, and the spacing of the coils.

And this also decides which vehicle it is suitable for. A light commercial vehicle has springs that are robust and fairly stiff.

On a small passenger car, they are lighter, and more flexible.

The coils may be evenly spaced, or of uniform pitch, or unevenly spaced.

The wire can be the same thickness throughout, or it may taper towards the end of the spring.

The spring itself may be cylindrical, barrel-shaped, or conical.

Generally, a cylindrical spring, with uniform diameter wire, and uniform pitch, has a constant deflection rate. Its length reduces in direct proportion to the load applied.

When the pitch is varied, the deflection rate varies too. The spring is then said to have a progressive rate of deflection.

Similarly for varying wire diameter and the shape.

A spring with a progressive rate deflects readily under a light load, but increases its resistance as the load increases. This gives a softer ride.

As conical and barrel-shaped springs compress, they collapse into themselves. This gives a longer suspension travel for the length of the spring, than for a cylindrical spring. This gives a softer ride for light-load situations, and a harder ride for heavy load situations.

As a cylindrical coil compresses, it can become coil-bound, which limits its travel.

Coil springs can look alike but give very different load ratings, which are often color coded for identification.

They normally use rubber pads to prevent transmission of noise and vibration.