Most modern cars have disc brakes on the front wheels, and some have disc brakes on all four wheels. The function of the brake disc is to slow down or stop the car. When the brake pedal is pressed the brake pads “squeeze” the brake disc which generates friction.
Brake discs should be replaced when they are worn below the minimum thickness, worn unevenly, warped or heavily scored. Should be replaced in pairs with new brake pads fitted at the same time.