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The material of brake pads is the core factor determining their braking performance, service life and suitable scenarios. The formula and composition differences of different materials will directly affect key indicators such as the coefficient of friction, high-temperature resistance, noise and dust. At present, the mainstream brake pad materials are divided into three categories, and their performance influences are as follows:   1.Metal-based brake pads (semi-metallic/low-metal formula)   Core components： steel fiber, ferroalloy powder, copper fiber (traditional formula) + phenolic resin + filler, with metal components accounting for 30%-60%. Performance impact： Advantages： Stable coefficient of friction (0.35-0.45), strong braking force, medium heat resistance (able to withstand 400-600℃), low price, suitable for mid-to-low-end fuel-powered family cars and commercial vehicles. Disadvantage: Metal materials have strong thermal conductivity and can easily transfer heat to the brake discs and calipers. Long-term high temperatures may cause the brake discs to deform. When braking, it makes a lot of noise and generates a large amount of black metal dust, which is prone to contaminating the wheel hub. The braking feel is rather hard at low temperatures. Compatible scenarios: Economy cars, vans, pickup trucks and other cost-sensitive vehicle models.   2. Ceramic-based brake pads   Core components: Ceramic fiber, mineral fiber, graphite + high-performance resin, no metal or low metal content. Performance impact： Advantages: The coefficient of friction is stable (0.38-0.48), and its high-temperature resistance is superior to that of metal brake pads (able to withstand 600-800℃), with a slight thermal fade phenomenon. The braking noise is extremely low, with almost no metal dust and will not contaminate the wheel hub. It has low thermal conductivity, which can protect brake discs and calipers and extend the service life of brake discs. The low-temperature braking response is fast and the feel is smooth. Disadvantages: The peak braking force is slightly lower than that of metal brake pads, and the braking confidence is slightly weaker when driving under heavy load or aggressively. The cost is 30% to 50% higher than that of metal brake pads. Compatible scenarios: Family sedans, SUVs, new energy vehicles (suitable for low noise and low dust requirements).   3. Carbon-ceramic/carbon fiber brake pads   Core components: carbon fiber, silicon carbide ceramic matrix + special resin, belonging to high-end composite materials. Performance impact： Advantages: Extremely strong heat resistance (able to withstand 800-1200℃), no obvious thermal fade after continuous sudden braking; It has an extremely high and stable coefficient of friction (0.45-0.55), and strong braking force. It weighs only one third of metal brake pads and can reduce the unsprung mass. The service life is up to 80,000 to 120,000 kilometers, which is 2 to 3 times that of traditional brake pads, and it hardly wears out the brake discs. Disadvantage: The cost is extremely high, being 5 to 10 times that of ceramic brake pads. In low-temperature environments (below -20℃), the coefficient of friction slightly decreases, and the initial braking feel is relatively soft. Occasionally, there is a slight abnormal noise when braking lightly at low speed. Adaptation scenarios: High-end performance cars, sports cars, high-performance versions of new energy vehicles (such as Tesla Model Y high-performance version), racing cars.

To determine whether a car's brake pads need to be replaced, a comprehensive judgment can be made through three methods: visual inspection, driving experience, and professional testing. The threshold for replacing brake pads varies slightly among different car models, but the core judgment criteria are the same, as follows:   1. Visual inspection: Check the thickness and wear marks   (1) Check the thickness: The standard thickness of the friction material of brake pads is approximately 10-15mm. When it wears down to 3-5mm, it is necessary to prepare for replacement. If the thickness is less than 2mm, it is in a high-risk state and must be replaced immediately; otherwise, the brake disc will be damaged. Inspection method: For family cars, you can directly observe the friction layer (the black part) of the brake pads through the gap of the wheel hub. By comparing it with the thickness of the backplate, you can make a preliminary judgment. If the wheel hub is blocked and cannot be observed, the tire needs to be removed for inspection.   (2) Check the wear mark: Almost all brake pads come with a wear warning plate/groove mark, which is the replacement critical point set by the manufacturer. When the friction material wears down to the same level as the warning plate, the brake pads will rub directly against the brake disc. At this point, they must be replaced.   2. Driving experience: Listen to the sound and feel the braking   (1) Listen to the warning noise: Some brake pads are equipped with metal warning plates. When they wear to the limit, a sharp metal friction sound (similar to "creaking" or "shrill scraping" sounds) will occur when braking or driving normally. This is the most obvious signal for replacement. Note: If there is a "dull sound" or "abnormal noise" when braking, but the thickness of the brake pads is sufficient, it may be due to foreign objects getting stuck or problems with the material of the brake pads. Cleaning or inspection is required.   (2) Feel the braking effect: If the braking distance significantly increases, the pedal becomes soft or drifts when stepping on the brake, or the vehicle body shakes during braking, and after ruling out faults in the brake fluid or brake discs, it is highly likely that the friction coefficient of the brake pads has decreased and they need to be replaced.   3. Professional inspection: Check the alarm lights and read the data   (1) Warning light: Some mid-to-high-end models are equipped with a brake pad wear warning system. When the brake pads wear to the limit, the "Brake System Failure Light" or the dedicated "Brake pad Warning Light" on the dashboard will light up. At this time, it is necessary to go to the store for inspection and replacement in a timely manner.   (2) Professional inspection: Go to a repair shop and measure the thickness of the brake pads with special tools. At the same time, check whether the brake discs have been worn out into deep grooves or deformed. If the brake discs are severely damaged, they need to be replaced simultaneously with the brake pads.   Supplement: Replacement precautions   It is recommended to replace brake pads in pairs on the same axis (left front + right front, or left rear + right rear) to avoid uneven braking force on both sides causing brake deviation. The wear rate of rear brake pads is usually slower than that of front brake pads (the front brake of a front-wheel drive vehicle bears about 70% of the braking force), but they still need to be inspected regularly and should not be ignored.

The working principle of automotive brake pads is essentially to convert the kinetic energy of the vehicle into thermal energy through friction, thereby achieving vehicle deceleration or stopping. The entire process is accomplished through the mechanical structure of the braking system and the principle of tribology in coordination. Specifically, it is divided into the following core steps:   1. Braking signal transmission and force amplification   When the driver steps on the brake pedal, the mechanical force of the pedal is transmitted to the brake master cylinder. The piston inside the master cylinder is compressed, pushing the brake fluid to flow in the sealed brake lines. For a hydraulic braking system, the brake fluid evenly transmits pressure to the brake calipers of each wheel. For pneumatic braking systems (mostly used in heavy vehicles such as trucks and buses), compressed air is used to push the caliper piston. This process will leverage the lever principle and the pressure characteristics of hydraulic/pneumatic systems to amplify the smaller pedal force applied by the driver several times to meet the powerful force required for braking.   2. The contact and adhesion between brake pads and brake discs   The piston inside the brake caliper extends outward under pressure, pushing the brake pads on both sides of the caliper (divided into inner brake pads and outer brake pads), causing them to quickly adhere to the surface of the brake disc that rotates synchronously with the wheel. The friction surface of the brake pad will completely press against the brake disc. At this point, the gap between the two is eliminated, and it enters the friction braking stage.   3. Frictional heat generation achieves kinetic energy consumption   When the friction material of the brake pad comes into contact with the brake disc, it will generate a strong frictional force. This frictional force will impede the rotation of the brake disc, and the brake disc is rigidly connected to the wheel, thereby hindering the rotation of the wheel. During this process, the kinetic energy of the car's movement is converted into heat energy through friction, and the heat is dissipated into the brake pads, brake discs and the surrounding air. When the kinetic energy of a vehicle is continuously consumed, its speed will gradually decrease until it comes to a complete stop.   4. Brake release and reset   When the driver releases the brake pedal, the pressure in the brake master cylinder is relieved and the pressure in the brake lines drops. The reset spring inside the brake caliper pulls the piston back to its original position, creating a new gap between the brake pads and the brake discs. The frictional effect disappears, and the wheels return to a free rotation state, thus completing the braking process.   Supplementary: Key factors affecting braking effect   The performance of friction materials: The coefficient of friction of brake pad friction materials directly determines the magnitude of braking force. High-temperature resistance can prevent the coefficient of friction from dropping sharply at high temperatures (i.e., "thermal fade"), ensuring the stability of continuous braking. The fit between brake pads and brake discs: The larger the fit area and the more uniform the pressure, the more stable the braking effect. Therefore, the processing accuracy of brake pads and the design of calipers are of vital importance. Heat dissipation efficiency: If the heat generated during braking cannot be dissipated in time, it will cause the temperature of the brake pads and brake discs to be too high. This not only reduces braking performance but may also accelerate the wear of the brake pads and even lead to braking failure.

By observing the appearance, testing the feel and checking the details, one can quickly distinguish the quality of brake pads and avoid purchasing inferior products. The specific methods are as follows:   1. Observe the appearance: Judge quality control from the details of workmanship   Inspection of the friction layer： High-quality brake pads: The surface of the friction layer is smooth and uniform, without obvious impurities, pores, cracks or chipping. The edges have regular chamfers (to reduce abnormal braking noise); The thickness of the new friction layer is approximately 10 to 15mm, with uniform thickness and no uneven thickness. Poor-quality brake pads: The surface of the friction layer is rough, with a distinct granular feel or impurities. There are many burrs on the edges and no chamfers. The thickness may be too thin (some merchants cut corners), and even signs of delamination and delamination may appear.   Inspection of steel back and coating： High-quality brake pads: The anti-rust coating on the steel back (metal base plate) surface is uniform and bright, free of rust, deformation and scratches. The matching sound-absorbing plates and shock-absorbing plates (made of rubber/sponge material) are firmly bonded and will not loosen when pressed. Poor-quality brake pads: The steel back has no anti-rust coating or the coating has peeled off, and the edges are prone to rust. The sound-absorbing sheet is stuck with low-quality glue and can be easily torn off. Even the sound-absorbing accessories are missing.   Identification integrity check： High-quality brake pads: The surface is clearly marked with the brand name, coefficient of friction grade (such as FF grade), OE number, production date, and execution standard (such as GB5763-2018), and the handwriting is clear and not easy to erase. Poor-quality brake pads: No marking at all or the marking is blurry, and the writing comes off easily when wiped. Even the logos of well-known brands are imitated, but the fonts and layouts are obviously different from the genuine ones.   2. Feel the texture: Judge the material and craftsmanship by touch   Press the friction layer by hand: The friction layer of high-quality brake pads is firm in texture, with no indentation or powder shedding when pressed. Poor-quality brake pads have a loose friction layer, are prone to chipping when pressed, and have a rough feel.   Weigh by hand: Under the same size, metal-based brake pads are heavier, ceramic-based brake pads are slightly lighter, and carbon-ceramic brake pads are the lightest. If the metal brake pads feel too light, it might be due to excessive use of cheap fillers and poor quality.   Adhesion test between the friction layer and the steel back: Bend the edge of the friction layer by hand. High-quality brake pads adhere firmly without loosening. Poor-quality brake pads may show signs of the friction layer separating from the steel back.   3. Check qualifications: Avoid counterfeit goods through certifications and channels   Verify authoritative certifications: It is necessary to check whether the product has ECE R90 certification, 3C certification (for the domestic market), and the test report that complies with the GB5763-2018 national standard. Products without certification are directly excluded.   Confirm the purchase channel: Give priority to choosing the brand's official flagship store, authorized dealers or regular auto parts stores; Avoid purchasing from unqualified street vendors or low-price online stores. Counterfeit brake pads often attract consumers with low prices, but their quality is not guaranteed at all.   Verify after-sales warranty: High-quality brand brake pads offer a warranty service ranging from 6 months to 1 year or 10,000 kilometers. The warranty terms will be marked on the packaging. Inferior products have no warranty commitment at all, and once problems occur, it is impossible to protect one's rights.