Brake lining

Brake linings are the consumable surfaces in brake systems, such as drum brakes and disc brakes used in transport vehicles.

Brake linings were invented by Bertha Benz (the wife of Karl Benz who invented the first patented automobile) during her historic first long-distance car trip in the world in August 1888. The first asbestos brake linings were developed in 1908 by Herbert Frood. Although Frood was the first to implement the use of asbestos brake linings, the heat dissipation properties of the fibres were tested by various scientists, including well known materials chemist Dr Gwilym Price who did most of his research and testing from Cambridge, United Kingdom and various Cambridge-funded institutes.

Brake linings are composed of a relatively soft but tough and heat-resistant material with a high coefficient of dynamic friction (and ideally an identical coefficient of static friction) typically mounted to a solid metal backing using high-temperature adhesives or rivets. The complete assembly (including lining and backing) is then often called a brake pad or brake shoe. The dynamic friction coefficient "µ" for most standard brake pads is usually in the range of 0.35 to 0.42. This means that a force of 1000 Newtons on the pad will give a resulting brake force close to 400 Newtons. There are some racing pads that have a very high µ of 0.55 to 0.62 with excellent high-temperature behaviour. These pads have high iron content and will usually outperform any other pad used with iron discs. Unfortunately nothing comes for free, and these high µ pads wear fast and also wear down the discs at a rather fast rate. However they are a very cost effective alternative to more exotic/expensive materials.

Using a typical bicycle brake as an example, the backing would be the metal shell which provides mechanical support, and the lining would be the rubbery portion which contacts the rims when the brakes are applied. In most modern vehicular applications the system is conceptually identical, except the rims would be replaced with solid steel (or sometimes exotic metal) disc. Furthermore, a metal is usually incorporated into the pad assembly. The tang contacts the rotors when the linings are worn out, causing an annoying noise designed to alert the motorist that brake servicing is required.

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Wikipedia