Only the front or only the rear brake discs have grooves which are caused by driving habits and uneven distribution of front and rear brake forces. If only one brake disc has a groove, the others are normal. This situation is generally caused by materials or external forces, and the reasons are as follows:

1. There is a foreign body caught between the brake disc and the brake pad, which happened to be caused by a foot brake;

2. It is caused by the unbalanced strength of the brake cylinder;

3. The manufacturing process of this brake pad is defective, resulting in uneven mixing of materials, causing the brake pad to be too hard or with large metal particles in the brake pad.