Vehicle braking system fade, or brake fade is the reduction in stopping power that can occur after repeated application of the brakes, especially in high load or high speed conditions. Brake fade can be a factor in any vehicle that utilizes a friction braking system including automobiles, trucks, motorcycles, airplanes, even bicycles. This article needs additional references or sources for verification. ... The Trikke is a Human Powered Vehicle (HPV) This article is about the means of transport. ... friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. ... Karl Benzs Velo model (1894) - entered into the first automobile race An automobile or motor car (usually shortened to just car) is a wheeled passenger vehicle that carries its own motor. ... The driver of this DAF tractor with an auto-transport semi-trailer truck prepares to offload Škoda Octavia cars in Cardiff, Wales For other articles with similar names, see Lorry (disambiguation) and truck (disambiguation). ... MotorCycle is the title of a 1993 album by rock band Daniel Amos, released on BAI Records. ... Fixed-wing aircraft is a term used to refer to what are more commonly known as aeroplanes in Commonwealth English (excluding Canada) or airplanes in North American English. ... “Velo” redirects here. ...

Brake fade is caused by a buildup of heat in the braking surfaces and the subsequent changes and reactions in the brake system components and can be experienced with both drum brakes and disk brakes. Loss of stopping power, or fade, can be caused by friction fade, mechanical fade, or fluid fade. Brake fade can be significantly reduced by appropriate equipment and materials design and selection.

Brake fade occurs most often during high performance driving or when going down a long, steep hill. Owing to their configuration this is more prevalent in drum brakes. Disk brakes are much more resistant to brake fade and have come to be a standard feature in front brakes for most vehicles. It has been suggested that this article or section be merged into Vehicle brake. ... On automobiles, disc brakes are located within the wheel The disc brake is a device for slowing or stopping the rotation of a wheel. ...

Causes of brake fade

The reduction of friction termed brake fade is caused when the temperature reaches the "kneepoint" on the temperature-friction curve. [All brake lining is cured under mechanical pressure following a heating & cooling curve, heating the friction material up to 450°F to "cure" (cross-link) the phenolic resin thermoset polymers: There is no melting of the binding resins, because phenolic resins are thermoset, not thermoplastic] In this form of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels "spongy". This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance. Brake fluid is a type of hydraulic fluid used in brake applications in automobiles and light trucks. ... Close-up of a disc brake on a car Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. ...

Fade in drum brakes

Truck air brakes can fade due to expansion if improperly adjusted

High sensitivity of Drum brakes to small changes in friction coefficient can severely affect their performance. Fade at high temperatures, caused by dissipating kinetic energy while slowing a vehicle can cause loss of braking while an increase can cause lock-up. Because fade may not occur simultaneously on all wheels, differential braking can cause a vehicle to swerve. As fade increases, typically while descending long steep grades, brakes on all wheels may fail and cause a runaway. High sensitivity to changes in friction coefficient is inherent to expanding-shoe drum brakes, the type formerly used on most cars and still used on many trucks, especially for rear axles and trailers. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... It has been suggested that this article or section be merged into Vehicle brake. ... The kinetic energy of an object is the extra energy which it possesses due to its motion. ...

The inherent design problem of drum brakes, from which their sensitivity to small changes in friction coefficient arises, is self energizing servo by which brake shoes, when pressed against the drum, push themselves into contact by their own friction, giving responses from lock-up to complete failure. For example, on damp mornings, drum brakes can lock on first application, skidding to a stop even after the brake pedal has been released. This occurs because servo or positive feedback magnifies small changes in friction coefficient. In contrast, with disk brakes, that have no servo effect, these small changes in friction coefficient are hardly noticeable. Look up servo in Wiktionary, the free dictionary. ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ...

Brake failure was also caused by brake drum thermal expansion in which brake shoe clearance had become excessive from wear. This was remedied in the 1950s by self adjusting brakes.^[1] Maladjustment with wear is still a factor in trucks that use drum air brakes. ^[2] Another explanation for brake failure was that heated brake shoes evaporated to generate gas that separate them from the drum. When experiencing brake fade one could readily imagine such effects even though they are physically impossible, considering the volume of gas required for such an effect, the gas bearing needing replenishment as fast as the disk moves, it having no gas on its surface when entering the interface. After cooling, faded brakes perform as well as before with no visible change to brake shoes. In contrast, disk brakes, using much the same materials, operate well even with glowing hot disks (color vs. temperature)' ^{[citation needed]} It has been suggested that this article or section be merged into Vehicle brake. ... Fluid bearings are bearings which solely support the bearings loads on a thin layer of liquid or gas. ...

Long dual-tire skid marks on highways, made by trucks with drum brakes, are visible examples of non-linearity between brake response and pedal pressure. Large trucks still use drum brakes because they are economical and fit easily where an equivalent disk brake would not. More recently disk brakes for trucks have been promoted listing features such as no fade, made possible in the absence of brake servo.^[3] Their disk surfaces also have no gas venting features. Although railroads use disk brakes, they do not use drum brakes because steel wheels skid too easily and cause flat spots, an effect that can be heard occasionally as a thumping sound on passing trains.

Controlling fade through driving technique

Brake fade and rotor warping can be reduced through proper braking technique; When running down a long downgrade that would require braking simply select a lower gear (for automatic transmissions this may necessitate a brief application of the throttle after selecting the gear). Also, periodic, rather than continuous application of the brakes will allow them to cool between applications. Continuous light application of the brakes can be particularly destructive in both wear and adding heat to the brake system. Finally, new brakes should be used as gently as possible for the first 100 miles or so to "break them in" and eliminate green fade.

Brake modification to reduce fade

High performance brake components provide enhanced stopping power by improving friction while reducing brake fade. Improved friction is provided by lining materials that have a higher coefficient of friction than stock brake pads while brake fade is reduced through the use of more expensive binding resins with a higher melting point along with slotted, drilled, or dimpled rotors that reduce the gaseous boundary layer in addition to providing enhanced heat dissipation. Heat buildup in brakes can be further addressed by body modifications that direct cold air to the brakes.

Both disc and drum brakes can be improved by any technique that removes heat from the braking surfaces.

Drum brake fade can be reduced and overall performance enhanced somewhat by an old "hot rodder" technique of drum drilling. A carefully chosen pattern of holes is drilled through the drum working section; drum rotation centrifugally pumps a small amount air through the shoe to drum gap, removing heat; fade caused by water-wet brakes is reduced since the water is centrifugally driven out; and some brake-material dust exits the holes. Brake drum drilling requires careful detailed knowledge of brake drum physics and is an advanced technique probably best left to professionals. There are performance-brake shops that will make the necessary modifications safely. The Bugatti Veyron for example has turbine cooled brakes that reduce fade to almost nothing considering the speeds it is braking from.

References and sources

1. ^ Spartan Engineering 1959; Disk Brakes; accessed 2007-02-26
2. ^ http://www.roadranger.com/ecm/groups/public/@pub/@roadranger/documents/content/rr_axag-0300.pdf; Dana® Spicer ® Trailer Axles & Brakes; Application Guide AXAG-0300 March 2006; See "Brake Fade" in glossary; accessed 2007-02-26
3. ^ http://www.roadranger.com/Roadranger/productssolutions/brakes/airdiscbrakes/index.htm

• http://www.tirerack.com/brakes/tech/techpage.jsp?techid=78&currentpage=87 Tire Rack article accessed 2006-10-23

• Friction Material Standards Institute