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Chassis Basic Information
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Springs are the foundation of the suspension and support the weight of the vehicle. The installed height of the springs determines the ride height of the chassis and suspension, which in turn affects camber, caster and toe alignment.


Springs come in several basic varieties: coil, leaf, torsion, air and helper.

Coil springs are made of steel wire wound in the shape of a coil. Coil spacing as well as the size of the wire and the overall diameter of the spring determine its stiffness (spring rate). Coil springs may be standard, heavy-duty or variable rate. Standard springs have a "linear" spring rate which means the amount of resistance the spring offers is directly proportional to how far the spring is compressed. A spring rated at 200 lbs. per inch will deflect one inch for every 200 lbs. of load.

Heavy-duty springs have a higher (stiffer) spring rate than the original. They are for applications that require additional load carrying capability, such as station wagons, trucks, vans, RVs or vehicles used for towing. Because they increase ride harshness, many customers may prefer a variable rate spring.

Variable rate springs become progressively stiffer the more they are compressed. This allows the spring to give a normal ride under light loads, but to act like a heavy-duty spring when extra weight is added. As a variable rate spring is compressed, the closer spaced coils (which have a lower spring rate) come together shifting the load to the remaining coils which are further apart and have a stiffer rate. When the load is removed, the closer spaced coils spread out to provide a normal ride. Variable rate springs are often installed as a suspension upgrade when extra load carrying capacity is needed.

Coil springs can sag with age, and should be replaced if ride height is less than factory specifications. Breakage or insufficient load carrying capacity are other reasons for replacement.

Coil springs should usually be replaced in matched pairs to maintain even side-to-side ride height. A spring compressor is required to remove front springs and those on MacPherson struts. But rear springs can often be removed by disconnecting the rear shocks and lowering the rear axle.

CAUTION: A spring stores considerable energy. If using a spring compressor, make sure it is properly positioned and has a secure grip on the spring coils. Handle a compressed spring with extreme caution, and do not attempt to remove the spring compressor until spring tension has been fully released by backing off the compressor.

Single or multi-leaf are used primarily for rear-wheel drive rear suspensions, but also 4X4 truck suspensions front and rear as well as some FWD live rear axle suspensions. The springs are attached to the axle with U-bolts and often have a centering pin. Reasons for replacing leaf springs include sag and breakage. Like coil springs, leaf springs should be replaced in matched pairs.

Some vehicles (Chevrolet Corvette, Lumina and Astro van) have composite fiberglass transverse leaf springs. This type of spring is much lighter than a conventional steel spring, and also resists sag much better than steel.

This type of spring consists of a steel bar (mounted horizontally) that is twisted to support the weight of the vehicle. One end of the torsion is mounted in the frame or chassis while the other is attached to a control arm or trailing arm. Torsion bars are used in place of coil or leaf springs on some vehicles (GMC pickups, older Chrysler cars, Volkswagens, etc.), and allow ride height to be adjusted to compensate for sag. Reasons for replacement include breakage and sag.

These are air-filled rubber or elastomer bags that are pressurized to provide support to the suspension. Air springs are used in place of conventional coil springs as original equipment on some vehicles (certain Lincoln and Ford models), and are part of an electronic ride control system that automatically maintains ride height. The primary reason for replacement is air leakage. Aftermarket air springs can be installed inside coil springs or between the axle and frame to provide additional lift support for handling overloads or towing.

These are springs designed to increase a vehicle's load carrying capacity. They include bolt-on leaf springs for use with existing leaf springs, bolt-on coil springs that are installed between the axle and frame, and cone or barrel shaped rubber springs (used in trucks primarily) that fit between the axle and frame for added support.

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