A coilover is an automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 suspension

Suspension (vehicle)

Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

 device. "Coilover" is short for "coil spring over strut". It consists of a shock absorber

Shock absorber

A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...

 with a coil spring

Coil spring

A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces...

 encircling it. The shock absorber and spring are assembled as a unit prior to installation, and are replaced as a unit when the shock absorber has leaked. This provides for optimal damping without torsional loads. Some coilovers allow adjustment of ride height

Ride height

Ride height is the amount of space between the base of an automobile tire and the underside of the chassis; or, more properly, to the shortest distance between a flat, level surface, and any part of a vehicle other than those parts designed to contact the ground...

 and stiffness, using a simple threaded spring perch similar to a nut

Nut (hardware)

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts...

. More advanced adjustable coilover systems will use a threaded shock body, coupled with an adjustable lower mount for ride height

Ride height

Ride height is the amount of space between the base of an automobile tire and the underside of the chassis; or, more properly, to the shortest distance between a flat, level surface, and any part of a vehicle other than those parts designed to contact the ground...

 adjustment, while an adjustment knob is used to adjust damping

Damping

In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...

, commonly referred to as "stiffness." Spring rate also plays a role in stiffness.

The coilover is a basic component of the MacPherson strut

MacPherson strut

The MacPherson strut is a type of car suspension system which uses the axis of a telescopic damper as the upper steering pivot. It is widely used in modern vehicles and named after Earle S. MacPherson, who developed the design.-History:...

 suspension system, which is distinguished from other arrangements by employing a particular design of anti-roll bar

Sway bar

A sway bar or anti-roll bar or stabilizer bar is a part of an automobile suspension that helps reduce the roll of a vehicle that is induced by cornering or road irregularities. It connects opposite wheels together through short lever arms linked by a torsion spring...

as a longitudinal constraint. This was the first widespread use of the coilover in automobile suspensions, but there are other designs. The word coilover should not be considered a synonym for the MacPherson strut arrangement.

Coilovers should not be confused with struts or independently mounted shock absorbers.

Coilover suspension systems have become a popular staple in the automotive aftermarket. Once limited to racing teams with the research and development budget to create performance parts, these suspension systems are now widely available from most online and retail aftermarket auto part merchants. There are 2 different types of coilovers, full coilovers and slip on coilovers. The full coilovers are matched up with a shock from the factory, while slip on coilovers are mostly just adjustible springs.

Coilover Alternatives

A Coilover is not to be confused with the Shock absorber and Spring setup (Strut), Coilover's are totally independent and do not require extra parts i.e. Bumpstops, Ball Joints, Spring cushions etc.
Many people state that they are the same but this is a busted Myth, hence the reason that High performance cars use independent coilover's to increase road grip, handling and comfort.
On a lower budget, people will install a 'Lowering kit' consisting of a spring that is of different measurement in length (mm) and fit Aftermarket Shock Absorbers to increase comfort and handling on tighter corners where body roll may hinder performance. Coilovers come adjustable or a fixed length and normally bolt straight to a car instead of using tools (Spring compressors) to fit a shock absorber and a spring to.
While they are generally more expensive (up to 90% more), they still offer the greatest amount of comfort and handling compared to the earlier, strut-mounted type.

External links

• http://www.pirate4x4.com/tech/billavista/coilovers/Part_1/, for an in-depth explanation of coilovers and their function.