View source for Coilover

{{Short description|Automobile suspension device}}
{{Use dmy dates|date=January 2023}}
[[File:Coilovers.jpg|thumb|right|240px|A set of coilovers.]]
[[File:Lot007.jpg|thumb|right|240px|Coilover used in the [[double wishbone]] suspension on a [[Lotus Seven|Lotus 7]].]]
[[File:Demi train avant microcar virgo bts cpi 2003.jpg|thumb|Coilover visible in the front suspension of a [[Microcar Virgo]]]]
A '''coilover''' is an [[automobile]] [[suspension (vehicle)|suspension]] device. The name coilover is an [[abbreviation]] of "coil over shock absorber".<ref name=burger>{{cite book |author=Steve Hendrickson Gerry Burger |title=Hot Rodder's Bible : The Ultimate Guide to Building Your Dream Machine |url=https://books.google.com/books?id=5gSgvG7JNp0C&pg=PA179 |publisher=MotorBooks International |isbn=978-1-61060-963-0 |pages=179–}}</ref>

== Description ==
Coilovers are found on many vehicles, from [[Radio-controlled car|RC cars]] to normal passenger cars, race cars and [[Four-wheel drive|4x4]] vehicles. They are sometimes used as a factory suspension option on new cars. Coilovers are used in [[double wishbone suspension]] systems,<ref name="happiansmith">{{cite book |author=Julian Happian-Smith |title=An Introduction to Modern Vehicle Design |url=https://books.google.com/books?id=36kg2DJiy7cC&pg=PA285 |year=2001 |publisher=Elsevier |isbn=978-0-7506-5044-1 |pages=285–}}</ref> and are often a component of [[MacPherson strut]]s.<ref name="gilles">{{cite book |author=Tim Gilles |title=Automotive Chassis: Brakes, Suspension, and Steering |url=https://books.google.com/books?id=mNIhYSCBfmUC&pg=PA329 |year=2005 |publisher=Cengage Learning |isbn=1-4018-5630-6 |pages=329–}}</ref>

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.<ref>{{Cite web |url=http://www.aptuned.com/blog/coilovers-vs-springs-what-are-coilovers-and-whats-better.html |title=Coilovers vs Springs – What are coilovers and what's better? |website=www.aptuned.com |language=en-US |access-date=10 June 2018}}</ref>

There are a large number of companies who make [[Aftermarket (merchandise)|aftermarket]] coilovers for vehicles, many of which allow the customer to adjust various settings such as [[ride height]] and [[Damping ratio|damping]]. [[Camber angle|Camber]] and [[caster angle]]s can also be adjusted if the car's suspension allows, and if the coilovers are supplied with adjustable top mounts.<ref>{{Cite web |url=https://low-offset.com/guides/coilovers-vs-lowering-springs-which-is-better/ |title=Coilovers vs Lowering Springs: Which is Better? |last=Team |first=Low Offset |date=5 June 2018 |website=Low Offset |language=en-US |access-date=11 January 2019}}</ref> This high degree of adjustment is what gives coilovers an advantage over typical MacPherson struts.

Coilovers can be used to lower the vehicle's [[Center of mass|centre of gravity]], and to increase the [[Body roll|roll]] stiffness of the vehicle to reduce [[weight transfer]] when the vehicle changes direction.<ref>{{Cite web |url=http://www.schoolphysics.co.uk/age11-14/Mechanics/Statics/text/Stability_/index.html |title=schoolphysics ::Welcome:: |website=www.schoolphysics.co.uk |access-date=11 January 2019}}</ref>

== Components ==
A coilover consists of a [[shock absorber|damper]], with a [[coil spring]] 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 (engineering)|preload]], adjusted using a simple threaded spring perch similar to a [[nut (hardware)|nut]]. Alternatively, the damper's threaded body is matched to a threaded bottom mount which allows [[ride height]] 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]]<ref name="tanner">{{cite book |url=https://books.google.com/books?id=wvnQbYLEj6wC&pg=PA113 |title=How to Build a High-Performance Mazda Miata MX-5 |author=Keith Tanner |date=2 December 2010 |publisher=Motorbooks |isbn=978-1-61060-970-8 |pages=113–}}</ref> or by adjusting the stiffness of the damper.

Coilovers are made up of several components, including the damper, coil spring, [[Bushing (isolator)|bushing]], bump stops, upper and lower mounts, various nuts and washers, threaded sleeves, and collars.<ref>{{Cite news |url=http://www.superstreetonline.com/how-to/chassis-suspension/sstp-1303-how-a-coilover-works/ |title=How A Coilover Works – Super Street Magazine |date=9 April 2013 |work=SuperStreetOnline |access-date=25 April 2018 |language=en-US}}</ref>

=== 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.<ref name=":0" />

==== Spring preload ====
[[Preload (engineering)|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.<ref name=":0" />

=== 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.<ref name=":0" />

=== 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,<ref>{{cite web |last1=Tune |first1=Drive |title=Which is Best? Height Adjustment |url=https://www.youtube.com/watch?v=QYOPXmH4yQs |archive-url=https://ghostarchive.org/varchive/youtube/20211222/QYOPXmH4yQs |archive-date=22 December 2021 |url-status=live |website=YouTube|date=22 May 2019 }}{{cbignore}}</ref> 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.<ref name=":0">{{Cite web |url=http://www.superstreetonline.com/how-to/chassis-suspension/sstp-1303-how-a-coilover-works/ |title=How A Coilover Works – Super Street Magazine |date=9 April 2013 |website=SuperStreetOnline |language=en |access-date=14 February 2019}}</ref>
* Compression and rebound: The stiffness of the [[Compression (physics)|compression]] 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.<ref name=":0" />

== See also ==
* [[Automotive suspension design]]
* [[Chapman strut]]
* [[Strut bar]]
* [[Anti-roll bar]]

== References ==
{{Reflist}}
11. [https://www.modifiedrides.net/news/carguides/how-to-install-coilovers-on-your-car.html How to install coilovers on your vehicle] ModifiedRides. 24th May 2021. Retrieved 19th March 2024.

== External links ==

* ''[http://www.pirate4x4.com/tech/billavista/coilovers/Part_1/ in-depth explanation of coilovers and their function.]'' ([http://www.pirate4x4.com/tech/billavista/coilovers/Part_2/ Part 2])
* ''{{usurped|1=[https://web.archive.org/web/20100428005523/http://www.corbymotorsport.com/tuning_guide.php article related to setting up coilovers]}}''
* ''[http://accutuneoffroad.com/articles/shock-tuning-101/ how to tune rebuildable coilovers]''

[[Category:Shock absorbers]]
[[Category:Automotive suspension technologies]]
[[Category:Telescopic shock absorbers]]