How deep should the grooves on brake discs be before replacement?
2 Answers
Brake discs should be replaced when the groove depth on both sides exceeds 1 millimeter. If the grooves on the brake discs are not deep, the brake pads can be removed and smoothed with coarse sandpaper. After reinstalling the sanded brake pads, the grooves on the brake discs can be eliminated during use. Alternatively, softer brake pads can be chosen; although they wear out faster, they are less likely to cause grooves on the brake discs. Simply put, a brake disc is a rotating disc that turns as the vehicle moves. The brake caliper clamps the brake disc to generate braking force, slowing down or stopping the vehicle when the brakes are applied. Brake discs offer effective braking performance and are easier to maintain compared to drum brakes.
I think brake discs need to be replaced when the grooves are too deep. With over a decade of driving experience, my rule of thumb is that when the groove depth exceeds 1.5 mm, it becomes a serious issue. Last month, my car started making unusual noises, and upon inspection, the grooves were as deep as 1.8 mm—the edges of the disc looked gnawed, which were marks left by worn brake pads. I immediately replaced the discs because braking at high speeds could easily lead to skidding otherwise. Now, I regularly measure with calipers—new discs are typically 22 mm thick, with a minimum safe thickness around 19 mm. Grooves reduce this thickness, and once they exceed 1.5 mm, you're nearing the limit. Remember, don’t wait until the discs warp or crack—that’s even more dangerous. Pay attention to vibrations or unusual noises while driving—they’re warning signs.
