What is the coefficient of friction?

One of the important criteria when evaluating a brake pad is the 'coefficient of friction'. The coefficient of friction is the ratio of the force of friction between two surfaces and the force pressing them together. The smaller the coefficient of friction, the smaller the force that is required for the two surfaces to slip. The higher the coefficient of friction, the stronger the force that is necessary for the two surfaces to slip. The coefficient of friction is 1 when 100 kg of force (parallel to the ground) is required to move an object that weighs 100kg. If the same object can be moved with 50 kg of force. The coefficient of friction is 0.5. When calculating the coefficient of friction for the braking of a car, the braking torque that occurs when braking, and the fluid pressure that was required to apply the brake pad is used.

Coefficient of Friction

In general, OEM brake pads have a coefficient of friction of 0.3?0.4, and performance brake pads have a coefficient of friction of 0.4?0.5. The higher the coefficient of friction, the less fluid pressure (lighter push of the brake pedal) is required to create a high braking force. If the coefficient of friction is too high, there is too much friction and makes it very difficult to brake. The most important factor for the coefficient of friction is for the brake pads to reach its maximum friction level immediately after the brake pedal is stepped on. If the initial braking power is bad, it is commonly reffered to as brake pads that do not work well (Having bad initial bite). The second important factor is the stability of the coefficient of friction at various temperatures. It is common for the coefficient of friction to be lower at low and extremely high temperatures. This is a problem because there will not be enough braking power for street-use if the temperature is too low. Another problem is the decrease of the coefficient of friction at extremely high temperatures. Users who drive on race circuits need stable braking power even in those conditions. A quality racing brake pad will have stable performance from start to finish. The third important factor is the stability of the coefficient of friction at different vehicle speeds. Brake pads will be dangerous if a stable coefficient of friction was achieved during braking at 60km/h but unstable at 180km/h, selling the product would not be possible. At DIXCEL, we are constantly doing research and development to come up with a brake compound that has stable yet high coefficient of friction. To increase the coefficient of friction and stabilize the brake compound, materials like bronze, steel fibre, fibreglass, Kevlar, ceramic, titanium, carbon, etc are very popular. It is the ongoing challenge at every brake manufacturer to make the mixture of the materials to make the best brake pad.

What is fade resistance?

illust pad03Fade resistance is evaluated by (1) the temperature at which brake fade occurs, and (2) how little the coefficient of friction changes after brake fade occurs. Brake fade is the decrease in braking power. Brake fade occurs when high temperatures causes a part of the resin material to vaporize. This creates a film between the disc and pad, which significant decrease the coefficient of friction. In general, OEM pads have a fade point (the temperature at which brake fade occurs) of around 300??350?. Performance brake pads usually have a fade point around 400??700?. (The fade point varies by material and the type of use.) Performance brake pads are made to have a higher fade resistance rate to minimizes the decrease of the coefficient of friction, even after brake fade occurs. The fade resistance rate is based on ratio of the coefficient of friction before and after the brake fade, so 100% would mean no change in the coefficient of friction. In general, OEM brake pads have a fade resistance rate of 40?50% where as performance brake pads have 60?80%. At DIXCEL, our goal is to increase the temperature at which our brakes fade and minimize the decrease of the coefficient of friction after brake fade. The research and development is ongoing to come up with better mixture of resins and materials to sell the best brake pads.

About brake pad wear

illust pad04A common thinking is that 'performance pads have faster wear rate compared to OEM pads'. This is neither false or true, since the wear rate can vary. This is because pad wear rate is different depending on the temperature of the brake pads. The graph on the right shows the wear differences of the OEM brake pads to our performance pads; the M and Z type pads. The values are the measurement of pad wear after 0.4G braking from 80km/h, which was repeated 1000 times for each type of pad and each temperature. By looking at the graph, it is easy to see how the pad wear rate increases significantly as the pad temperature rises. OEM pads have a low wear rate when pad temperature is below 150?, but have a much higher wear rate when the pad temperatures are above 300?. When pad temperatures reach above 300?, brake fade occurs for the OEM pads, and become almost useless in terms of braking power. Performance pads are designed for use on race circuits and for street performance, so they are developed to have optimal pad wear rate at temperatures around 250??600?. At lower temperatures, the performance pads will have higher wear rate at lower temperatures when compared to the wear rate of OEM pads at low temperatures. If you are going to use your brake pads for ordinary street use, the statement 'performance pads have faster wear rate compared to OEM pads' will be true. Performance pads are for users who need pads for use on race circuit and for street performance, that last longer, safer, and superior performance compared to the OEM pads.

About the pad wear sensors

illust pad05The pad wear sensors, also known as pad wear indicators, let the users know when the pads need replacement. There are two different types of pad wear sensors, mechanical and electric. The mechanical type generates a screeching noise when the metal clip attached to the pad comes in contact with the disc, to indicate the need for pad replacement. The electric type turns on a warning lamp on the instrumental panel of the car when the electric wire built into the pad becomes disconnected, to indicate need for pad replacement. Most Japanese and American cars use the mechanical type. Some Japanese luxury cars and most European cars use the electric type. There are two types of electric pad sensors. BMW, Mercedes, etc, use detachable wear lead wires. The other type is the built-in type, which is used by VW, Audi, etc. The wear lead wire is connected to the brake pad during the manufacturing process, therefore not detachable. In addition to the Premium series which have the built-in sensors as original, we also carry built-in sensors on select models on other pad types. (Please check the application table for details)
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Brake pads for Atari

Street use only

It depends on combination of pads and conditions of road you drive on, it takes roughly 300km?1,000km of running-in on ordinary roads. During that period, please refrain from fast or abrupt driving or do not drive in a way as to force the temperature up. Running in of rotors will be completed simply via normal driving.

Circuit use

istortion or cracks in rotors happen easier if optimum driving on a circuit is conducted straight from the beginning this in turn causes judders. When using a new rotor for the first time on a circuit, start with 50% braking for about 5 minutes and then go back to the pit once and take at least 5 minutes interval. After that, repeat 70?80% braking for about 10 minutes. Pit in again and take an interval of about 10 minutes. After that, gradually increase from 80% to 100% braking and the running in of rotors on circuit is completed.