Is It Necessary To Replace Both Brake Discs And Brake Pads Together?

In car maintenance, brake system maintenance is directly related to driving safety. As core components,brake discs and brake padsare always a focus of attention for car owners. Many people wonder: Do they need to replace the brake discs together with the brake pads? In fact, the two don't necessarily need to be replaced together; a comprehensive decision should be made based on factors such as actual wear and tear and usage.

1.The Relationship Between Brake Discs and Brake Pads: Mutually Supportive, Wear-Linked

Brake discs and brake pads are a "friction partner": When braking, the brake pads press against the discs through the caliper, using friction to slow the vehicle. This friction causes wear on both. Brake pads are "considered wear parts" and are made of softer materials (mostly metal, ceramic, or composite materials) and wear more quickly. Brake discs are made of harder materials (commonly cast iron, carbon ceramic, etc.) and wear more slowly, but they also experience wear with long-term use. Under normal circumstances, brake pads typically need to be replaced every 30,000-50,000 kilometers (depending on driving habits and road conditions; frequent hard braking can significantly shorten their lifespan). Brake discs, on the other hand, have a longer lifespan, generally reaching 80,000-120,000 kilometers. Therefore, in most cases, it's recommended to replace the brake discs only after replacing the pads two or three times, rather than replacing them simultaneously.

2.When are brake discs and pads replaced simultaneously?

While simultaneous replacement isn't mandatory, it's recommended to replace both brake discs and pads to ensure stable braking performance in the following situations:

(1) Excessive brake disc wear.

Brake discs are typically marked with a "minimum safe thickness" (e.g., 28mm; if worn below 25mm, replacement is required). If the thickness does not meet the standard, or if scratches, grooves, or cracks deeper than 0.5mm appear on the surface, even if the brake pads have just been replaced, the brake discs should be replaced simultaneously. Otherwise, the uneven disc surface will cause uneven force on the new brake pads, resulting in unusual brake squeal, vibration, or even localized overheating and thermal decay.

(2) "Matched wear" of brake pads and brake discs.

If brake pads have been worn excessively (e.g., until the metal backing is exposed) due to long-term non-replacement, they may directly rub against the brake disc, causing surface erosion, deformation, or "step-like" wear. In this case, the damaged brake disc will damage the friction surface of the new brake pad, resulting in reduced braking performance and must be replaced together.

(3) Excessive mileage or age of the vehicle

If a vehicle has traveled over 100,000 kilometers and the brake discs have never been replaced, it is recommended to have them inspected, even if the surface appears smooth. Long-used brake discs may experience metal fatigue and reduced resistance to thermal degradation, making them more susceptible to braking force fluctuations when used with new brake pads. Especially in vehicles over six years old, the brake disc material may have degraded due to oxidation, significantly reducing performance.

(4)Pursuing optimal braking performance and consistency

For owners of performance or modified vehicles, or those who frequently drive on mountain roads or highways, replacing brake pads with brake discs of the same brand and specification ensures a perfect match in friction coefficient, hardness, and other parameters. This reduces braking jerks during the break-in period (usually 300-500 kilometers) and helps achieve optimal performance quickly. Furthermore, some high-end models feature a "factory-fit" brake system, and replacing individual components may affect overall balance.

3.In what situations is it appropriate to replace only the brake pads?

If the following conditions are met, you don't need to replace the brake discs when replacing the brake pads:

• The brake discs are relatively recent (less than 50,000 kilometers), have a smooth surface, no obvious scratches or rust, and are within a safe thickness (measured with a vernier caliper, with a deviation of no more than 0.3mm);

• The brake pads are evenly worn, with no uneven wear, cracks, or exposed metal backing, and the brake discs are not damaged by them;

• There are no abnormalities during daily braking (such as unusual noises, vibrations, or deviation), and the braking distance is similar to that of a new vehicle;

• The vehicle is a family car driven on gentle roads (primarily urban roads), and there are no extreme braking requirements.

In this case, simply replace the brake pads with those that meet the manufacturer's specifications (make sure to check the model year and displacement). After installation, perform a "break-in" procedure—avoid sudden braking for the first 200 kilometers, and keep the speed below 80 km/h. This will allow the new pads to gradually adhere to the old discs, and normal braking performance will be restored.

4.Replacement Considerations: Safety Determines Details

(1) Avoid Mixing and Matching, Focus on Matching.

Brake pad and disc materials must be compatible. For example, ceramic brake pads have a lower hardness and are suitable for cast iron brake discs; metal brake pads have a higher coefficient of friction and require high-temperature-resistant alloy brake discs. Mismatched materials can result in "disc chewing" (abnormal disc wear) or "weak braking."

(2) Choose reputable brands and be wary of low-price traps.

Low-quality brake discs may have casting defects (such as pores and cracks) and easily deform at high temperatures. Low-quality brake pads may contain impurities with excessive hardness, accelerating disc wear. We recommend choosing reputable brands such as Bosch, Ferodo, TRW, and ATE, as their products undergo rigorous testing and offer more stable performance.

(3) Perform a "brake reset" and inspection after replacement.

Some models (especially those with electronic parking brakes) require a "brake wheel cylinder reset" using specialized equipment after replacing the brake pads. Failure to do so may prevent the caliper from returning properly and cause brake pad wear. After installation, check the brake lines for leaks. During a test drive, pay special attention to ensuring the brake pedal travel and force are normal, and to check for any unusual noises or slippage.

(4) Regularly maintain your brake discs to extend their lifespan.

If you notice rust on your brake discs after daily parking (especially in humid environments or after long periods of parking), don't worry. Gently applying the brakes during short driving distances can remove the rust through friction. When washing your car, avoid using a high-pressure water jet directly on hot brake discs (immediately after driving) to prevent cracking caused by sudden cooling.

Replace as needed, prioritize safety. Whether to replace brake discs and brake pads together depends on the actual condition of the discs and the vehicle's usage. For most family cars, routine maintenance only requires replacing brake pads as needed, with regular inspections (recommended during every minor maintenance) of the disc thickness and surface condition. However, if the disc is worn beyond the specified limit, severely damaged, or if there is a "compatibility failure" with the brake pads, simultaneous replacement is essential.

Whichever method you choose, ensure stable braking performance and avoid ignoring safety risks due to excessive cost savings. Having your brake system regularly inspected by a professional technician ensures confidence in every braking operation.If you want to know more information about brake parts and system,you can visit our website:https://www.evfriction.com.  Or contact us by +86-13363216781,and email us by jessicabrakes12@gmail.com.