Should Brake Discs with Grooves Be Replaced?
4 Answers
Brake discs developing grooves is a normal phenomenon, and replacement is not necessary if it does not affect braking performance. Relevant details are as follows: 1. Most brake discs will develop scratches or grooves during use, mainly due to the material composition of the brake pads. Brake pads are made of a combination of various materials, including hard metal powders. If there are relatively large metal particles in the powder, friction between these particles and the brake disc will cause scratches or even grooves. This occurs because metal particles are quite hard and share the same material as the brake disc, leading to damage when they rub against each other, hence the grooves on the brake disc. 2. Brake discs should be replaced when the wear depth exceeds 2 millimeters. Generally, brake discs should be replaced after changing brake pads 2-3 times. If vibration occurs during braking, this may also indicate an issue with the brake disc, possibly due to uneven wear or deformation. In such cases, the brake disc should be removed and resurfaced using a lathe. If the problem persists, a new brake disc should be installed.
Having worked in car repairs for over a decade, I've seen countless brake disc groove issues. To check groove depth, stand a 1-yuan coin on its edge for comparison—if the groove is significantly deeper than the coin's thickness, replacement is needed. But context matters: if the steering wheel vibrates like a phone alert during braking or there's screeching metal noise, it's likely caused by excessive groove depth. Never assume resurfacing will suffice—overly thin discs dissipate heat poorly, risking brake pad damage from overheating. I recommend direct thickness measurement—most OEM discs are ~28mm thick; replacement is mandatory if worn below 25mm. Pro tip: always replace pads when changing discs, otherwise new discs will quickly regroove.
From a safety perspective, this issue should be considered: Grooves on brake discs indicate an uneven surface. When brake pads contact the disc surface, irregular friction occurs due to these grooves. The impact might not be noticeable during daily driving, but emergency braking performance can drop by 30%. Last week, we encountered a case where grooves caused extended braking distance. A depth of 0.8mm is the safety threshold—exceeding this requires immediate replacement. During inspection, don't just look at the surface; rotating the wheel reveals that the grooves actually form wavy depressions. Notably, frequent driving on gravel roads accelerates deep groove formation. In such cases, it's recommended to inspect the disc surface every 30,000 kilometers.
Brake disc grooves are essentially caused by metal fatigue fractures. During braking, the instantaneous friction temperature can reach 700°C, and repeated thermal expansion and contraction of the metal leads to cracks. Shallow grooves are considered normal wear, similar to tire wear indicators. When using measuring tools for inspection, I focus on three key metrics: groove depth, disc thickness, and flatness. Pay special attention to the groove location - those with jagged edges are more dangerous than smooth-centered ones. When concentric circular grooves resembling record grooves appear on the disc surface, they often accompany brake judder. It's recommended to inspect the disc surface every two brake pad replacements. If budget is limited, prioritize replacing front brake discs as they bear 70% of the braking force. Remember to perform a proper break-in after replacement, avoiding hard braking for the first 300 kilometers.
