Along with your tires, your brake pads are among the most important items on your car to get regular maintenance for. Most brake pads last between 30–50,000 miles, after which time their stopping power will be greatly reduced. Replacing them once this happens is vital to maintaining your car's ability to be driven safely, but why is replacement necessary at all? After all, there are not many other items on the average car which wear out on a regular schedule, so what makes brake pads so special? Keep reading to learn a bit about how your brake pads work and why replacing them is necessary.
Brakes Are Energy-Conversion Machines
Your brakes simply stop your car, right? This may be the end result, but the physics of what's actually happening are a bit more interesting. When your car is moving forward, it has kinetic energy, or the energy of motion. According to the conservation of energy law, that energy cannot be lost. Instead of simply stopping your car, your brakes are actually converting that energy of motion into heat. Since heat is a form of energy, the primary role of your brake pads is to convert energy.
Of course, this doesn't do much on its own to explain why your brake pads fail, but it's the first piece of the puzzle. The next step is to understand that your brake pads generate this heat through friction. The pads are compressed against your brake discs (also known as brake rotors). The friction that's generated is what slows your vehicle down, and this action turns the kinetic motion of the rotors into heat.
Pads Are Sacrificial
The friction between your pads and rotors and the heat generated by that friction is what causes the pads to ultimately wear down. Your brake pads are actually made up of several parts, including a backing plate that's usually made of steel, but it's the friction material that wears away. You can see this wear in action in the form of brake dust that tends to build up on wheels over time. This dust is the friction material from your brake pads that's been worn away by braking.
Modern brake pad friction materials are generally either organic, semi-metallic, or ceramic. Each has its own pros and cons, but they all serve the same purpose: to sacrifice themselves to the friction and heat that's necessary to successfully stop your car.
Pads Are To Be Replaced Regularly
Now that you understand why pads need to be replaced, it should be a bit easier to understand when to replace them. Although it's usually safe to follow manufacturer-recommended replacement schedules, driving habits can shorten and extend the life of your brake pads. If you hear squealing from your brakes, it usually means that the pads have worn down below 3mm and the metallic warning strip is making contact with the rotors. This means that a replacement is necessary. Likewise, a warning light on your dash means that the sacrificial pad wear sensor has been destroyed and your pads are now in need of replacement.
Once you see one of these signs, it's time to schedule a brake pad replacement as soon as possible.