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A coilover is an
automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarde ...
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
device. The name coilover is an abbreviation of "coil-over shock absorber".


Description

Coilovers are found on many vehicles, from
RC cars ''RC Cars'', also known as ''Smash Cars'' for the PlayStation 2 and PlayStation 3 versions, is a vehicular combat game developed by Creat Games for Microsoft Windows and PlayStation 2 in 2002-2003. Reception The game received "mixed or average ...
to normal passenger cars, race cars and 4x4 vehicles. They are sometimes used as a factory suspension option on new cars. Coilovers are used in
double wishbone suspension A double wishbone suspension is an independent suspension design for automobiles using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckl ...
systems, and are often a component of MacPherson struts. Two of the main types of coilovers are full coilovers and slip-on coilovers. Full coilovers are matched up with a shock absorber from the factory, while with slip-on coilovers, the dampers and springs are bought separately and then assembled. There are a large number of companies who make aftermarket coilovers for vehicles, many of which allow the customer to adjust various settings such as
ride height Ride height or ground clearance is the amount of space between the base of an automobile tire and the lowest point of the automobile (typically the axle); or, more properly, to the shortest distance between a flat, level surface, and the lowest p ...
and
damping Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples in ...
.
Camber Camber may refer to a variety of curvatures and angles: * Camber angle, the angle made by the wheels of a vehicle * Camber beam, an upward curvature of a joist to compensate for load deflection due in buildings * Camber thrust in bike technology * ...
and caster angles can also be adjusted if the car's suspension allows, and if the coilovers are supplied with adjustable top mounts. This high degree of adjustment is what gives coilovers an advantage over typical MacPherson struts. Coilovers can be used to lower the vehicle's
centre of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force ma ...
, and to increase the
roll Roll or Rolls may refer to: Movement about the longitudinal axis * Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis ** Roll (aviation) ...
stiffness of the vehicle to reduce
weight transfer Weight transfer and load transfer are two expressions used somewhat confusingly to describe two distinct effects: *the change in load borne by different wheels of even perfectly rigid vehicles during acceleration *the change in center of mas ...
when the vehicle changes direction.


Components

A coilover consists of a
damper A damper is a device that deadens, restrains, or depresses. It may refer to: Music * Damper pedal, a device that mutes musical tones, particularly in stringed instruments * A mute for various brass instruments Structure * Damper (flow), a mechan ...
, with a
coil spring A selection of conical coil springs The most common type of spring is the coil spring, which is made out of a long piece of metal that is wound around itself. Coil springs were in use in Roman times, evidence of this can be found in bronze Fib ...
encircling it. The damper and spring are assembled as a unit prior to installation, and are replaced as a unit when either of the sub-components fails. Some coilovers are adjustable. Most, if not all, adjustable coilovers have variable ride height and preload, adjusted using a simple threaded spring perch similar to a
nut Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds * Nut (hardware), fastener used with a bolt Nut or Nuts may also refer to: Arts, entertainment, and media Co ...
. Alternatively, the damper's threaded body is matched to a threaded bottom mount which allows
ride height Ride height or ground clearance is the amount of space between the base of an automobile tire and the lowest point of the automobile (typically the axle); or, more properly, to the shortest distance between a flat, level surface, and the lowest p ...
adjustment without affecting bump travel. Most coilovers also have adjustable dampers, which are usually adjusted with an adjustment knob on top of the damper. Stiffness can be changed by switching the spring for one with a different spring rate or by adjusting the stiffness of the damper. Coilovers are made up of several components, including the damper, coil spring, bushing, bump stops, upper and lower mounts, various nuts and washers, threaded sleeves, and collars.


Springs

The purpose of coilover springs is to prevent the chassis from bottoming out, support each individual wheel on the vehicle, and mitigate or reduce body roll when taking turns and cornering, particularly at higher speeds. The springs also help to reduce squatting when accelerating and diving when decelerating. They are often used to adjust the vehicle's ride height, which directly affects handling and comfort.


Spring preload

Preload is the pressure exerted on a spring over the distance it is compressed. A higher preload means a stiffer spring and a lower preload results in a softer spring with more travel. This is true if the coilover uses progressive springs. On coilovers with linear springs preload has no effect on spring rate. More preload can increase grip when cornering, but too much preload can make a spring too stiff. In coilovers with adjustable spring seats, linear rate springs and no helper or tender springs, ride height must be adjusted through preload. This can present a problem for vehicles whose ride height needs to be lowered but whose springs are already stiff enough.


Dampers

A mono-tube coilover is a single piston and rod assembly in a damping case in which both compression and rebound occur. A larger mono-tube shock will be able to displace more hydraulic fluid, providing a more sensitive response to small suspension movements than twin-tube shocks. A twin-tube coilover is more complex than a mono-tube assembly. Twin-tubes have an inner cylinder which moves up and down, and an outer cylinder which serves as a hydraulic reserve. This design allows for an increase in suspension stroke, which provides better ride quality and handling.


Adjustable coilovers

Adjustable coilovers allow adjustment of the vehicle's suspension in four main areas: * Roll stiffness: By fitting springs with a higher spring rate, roll stiffness can be increased. Likewise, a lower spring rate results in increased roll. * Ride height: By using threaded spring seats or threaded bottom brackets, the ride height of the vehicle can be raised or lowered. The bottom mount is a threaded sleeve with two adjuster nuts that are used to preload the coils and increase or decrease ride height. * Compression and rebound: The stiffness of the
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...
and rebound of the suspension can be adjusted if the coilovers use adjustable dampers. Adjustable dampers fall into three main categories: those that adjust compression only, those that adjust rebound only, those that adjust rebound and compression in parallel, and those that are adjustable for rebound and compression independently. This later category can be split further into dampers that have low-speed adjustment and those that have independent high- and low-speed adjustment. An example of high speed in the context of suspension movement would be a car hitting a bump; an example of slow speed movement would be a car changing direction. * Camber and caster: Some coilover suspension kits may also be supplied with adjustable top mounts. Depending on the design of the car's suspension these top mounts can allow the adjustment of camber and/or caster. Some coilovers use the car's original top mounts and are therefore not adjustable.


Compression & rebound

Compression occurs when the piston inside the damper is moved inwards, increasing the pressure of the fluid in the chamber. Adjusting compression changes the motion of the vehicle's unsprung weight, modifying how quickly weight will shift downwards towards the wheel. Rebound is the result of the piston moving back after having been compressed, resulting in compression of the fluid once more. Adjustments made to rebound control the motion of the vehicle's sprung weight, changing how rapidly weight will be shifted away from the wheel.


Coilover Alternatives

Nitrogen-charged struts can be used as a more stable alternative to coilovers since they do not unload or push off, increasing stability.


See also

*
Automotive suspension design Automotive suspension design is an aspect of automotive engineering, concerned with designing the suspension for cars and trucks. Suspension design for other vehicles is similar, though the process may not be as well established. The process en ...
*
Chapman strut The Chapman strut is a design of independent rear suspension used for light cars, particularly sports and racing cars. It takes its name from, and is best known for its use by, Colin Chapman of Lotus. The characteristic feature of the Chapma ...
*
Strut bar A strut bar, strut brace, or strut tower brace (STB) is an automotive suspension accessory on a monocoque or unibody chassis to provide extra stiffness between the strut towers. With a MacPherson strut suspension system where the spring and sho ...
*
Anti-roll bar An anti-roll bar (roll bar, anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) whee ...


References

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External links

*
in-depth explanation of coilovers and their function.
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Part 2
*
article related to setting up coilovers
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how to tune rebuildable coilovers
' Shock absorbers Automotive suspension technologies Telescopic shock absorbers