Brake pads incorporate friction material that absorbs heat generated during a braking application. As you brake to a stop, these pads lose their material; they will eventually require replacing.
The brake pads attach to your car's calipers. The pads are squeezed against both sides of the rotor during an application of the hydraulic brakes, essentially grinding the pads down. Auto shops often use percentages in referring to how much friction material remains on your car's brake pads. If you have 80 per cent brakes, it means your pads still have ample material left for brake use.
Your car may have the ability to alert you electronically of when you need to replace your brake pads. Otherwise, your brake pads might have spring-steel tabs that come into contact with the rotors---creating a squealing sound while braking---at the point when the pads have become worn down and require replacing.
Brake Pad Change
If your car doesn't have brake pads that include devices to let you know when they have worn down, the website RepairPal recommends that you replace them once you have 25 per cent of the material left. Your local mechanic or car dealer can replace your brake pads.