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[[File:Disk brake dsc03682.jpg|thumb|Close-up of a disc brake on a [[Renault]] car]]
A '''disc brake''' is a type of [[brake]] that uses the [[#Calipers|calipers]] to squeeze pairs of [[#Brake pads|pads]] against a disc or(sometimes called a [brake] rotor)<ref>{{cite web|last=Deaton |first=Jamie Page |title=How Brake Rotors Work |url= https://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-rotors.htm |publisher=HowStuffWorks |date=11 November 2008 |access-date=26 November 2017}}</ref> to create [[friction]].<ref>{{cite encyclopedia |title=Disc brake |url= https://www.merriam-webster.com/dictionary/disc%20brake |dictionary=Merriam-Webster Dictionary |date=16 November 2017 |access-date=26 November 2017}}</ref> There are two basic types of brake pad friction mechanisms: abrasive friction and [[adherent]]{{explain|date=December 2024}} friction. <ref>{{Cite web |year=2023 |title=Abrasive friction and adherent friction |url=https://www.centricparts.com/media/wysiwyg/technical-bulletins/TECH_BULLETIN_C22-01.pdf |website=Centricparts |page=1 }}</ref> This action slows the rotation of a shaft, such as a [[vehicle]] [[axle]], either to reduce its rotational speed or to hold it stationary. The energy of motion is converted into [[heat]], which must be dissipated to the environment.
[[Hydraulic brakes|Hydraulically]] [[Actuator|actuated]] disc brakes are the most commonly used mechanical device for slowing motor vehicles. The principles of a disc brake apply to almost any rotating shaft. The components include the disc, [[master cylinder]], and caliper, which contain at least one cylinder and two [[Brake pad|brake pads]] on both sides of the rotating disc.
The brake disc is the rotating part of a wheel's disc brake assembly, against which the brake pads are applied. The material is typically [[gray iron]],<ref name=Intro-Ihm/> a form of [[cast iron]]. The design of the discs varies. Some are solid, but others are hollowed out with fins or vanes joining the disc's two contact surfaces (usually included in the casting process). The weight and power of the vehicle determine the need for ventilated discs.<ref name="whatsnewAMC"/> The "ventilated" disc design helps to dissipate the generated heat and is commonly used on the more heavily loaded front discs.
Discs for motorcycles, bicycles, and many cars often have holes or slots cut through the disc. This is done for better [[heat dissipation]], to aid surface-water dispersal, to reduce noise, to reduce mass, or purely for marketingnon-functional cosmeticsaesthetics.{{Cn|date=August 2024}}
Slotted discs have shallow channels machined into the disc to aid in removing dust and gas. Slotting is preferred in most racing environments to remove gas and water and deglaze brake pads. Some discs are both drilled and slotted. Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, removing of material is beneficial to race vehicles since it keeps the pads soft and avoids [[Glass transition|vitrification]] of their surfaces. On the road, drilled or slotted discs still have a positive effect in wet conditions because the holes or slots prevent a film of water from building up between the disc and the pads.
Two-piece discs areconsist whenof thea centercentral mountingsection partcombined ofwith thea disc isseparately manufactured separately from the outer friction ring. The central section used for fitment is often called thea bell or hat because of its shape. It is commonly manufactured from an alloy such as a [[7075 aluminium alloy|7075 alloy]] and hard [[anodised]] for a lasting finish. The outer disc ring is usually manufacturedmade fromof [[Gray iron|grey iron]]. They can also be frommade of [[steel]] or [[Ceramic matrix composite|carbon ceramic]] for particular applications.{{Cn|date=August 2024}} These materials originated from motorsport use and are available in high-performance vehicles and aftermarket upgrades. Two-piece discs can be supplied as a fixed assembly with regular nuts, bolts, and washers or a more complicated floating system where drive bobbins allow the two parts of the brake disc to expand and contract at different rates, therefore, reducing the chance of a disc will warpwarping from overheating. Key advantages of a two-piece disc are a savingreduction inof critical [[Un sprung weight|un-sprung weight]] and the [[Dissipation factor|dissipation]] of heat from the disc surface through the alloy bell (hat). Both fixed and floating options have their drawbacks and advantages. Floating discs are prone to rattle and collection of debris and are best suited to motorsport, whereas fixed discs are best for road use.<ref>{{cite web|url= https://www.apracing.com/Info.aspx?InfoID=35&ProductID=1594 |title=AP Racing - Race Car - Brake Discs - Ventilated Discs |website=apracing.com |access-date=2018-11-21}}</ref>
==History==
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