1. Coefficient of friction:

The parameter that indicates the friction performance of the brake pad is called the friction coefficient. The friction coefficient roughly means how "sticky" the brake pad is. The more sticky the brake pad, the greater the resistance and the more sensitive the brake, but the worse the comfort and heat resistance.

High-temperature brake pads mean that the friction coefficient can be maintained at a higher temperature, and it does not necessarily mean that the friction coefficient of high-temperature brake pads is large. The grade of the brake pad is indicated by two English letters. The first one is to measure the friction coefficient at 4 points between 0~600 (315.5 degrees Celsius). If all of them are between 0.5~0.45, then the low temperature grade of the brake pad is F. Then take 10 points to measure the friction coefficient between 600~1112 (600 degrees) degrees Fahrenheit. If the high temperature grade is also F between 0.35~0.45, then this sheet is FF grade sheet. The friction coefficient level of the ceramic brake pads that is often said is this FF level.

The common E means that the friction coefficient is 0.25~0.35, F said above, and G means between 0.45~0.55. 1112 degrees Fahrenheit is about 600 degrees Celsius. High temperature allows the original coefficient of friction to be maintained at a higher temperature, so high-temperature pads are not necessarily sensitive, but many high-temperature pads also help to reach higher temperatures by increasing the coefficient of friction. The ordinary semi-metal brake pads we often say are EF grades. 

Most of the brake pads of automobile cars can achieve FF. No matter how high the friction coefficient is, the metal content of the pads will be large, and the brakes will sound, and the comfort will decrease. A car with a large axle will use methods such as large-diameter brake discs, ventilated discs, and scribed discs to increase braking force and slow down heat decay. 

EE grade: 0.25-0.35 is suitable for European and American cars, with relatively large brake pads and low friction coefficient; FF grade: 0.35-0.45 international standard friction coefficient; GG grade: 0.45-0.55 is suitable for European models; HH grade: 0.55-0.65 for racing cars. 

The way of braking is to convert the kinetic energy of the vehicle into heat energy and dissipate it by friction. The faster the heat dissipation, the faster the deceleration. There is also a balance between heat increase and heat dissipation. If the heat increases too much and exceeds the limit that the braking part can bear, the parts change and the braking ability will be lost. This situation is mainly manifested in the heat attenuation of the braking system. It is caused by the ablation of the surface of the brake pad by exceeding the tolerance temperature of the brake pad.

2. Explanation of heat accumulation and Heat attenuation: 

Heat accumulation: due to heat generated by friction, when the heat cannot be dissipated 100%, cumulative accumulation will occur, and heat accumulation will cause the temperature to rise. 

Heat attenuation: When the heat accumulates to a certain extent and exceeds the limit that the friction material can withstand, the material will be burned, and the braking force will drop significantly to cause heat attenuation, that is, stepping on the brakes will not work. 

Therefore, the tolerance temperature of brake pads is a very important parameter. Usually, civil brake pads are limited between 200℉~600℉, and brake pads with different coefficients of performance are manufactured in this range.