Behind The Curve: Why Are Brake Pads Shaped Like That?

Looking at disc brakes, have you ever wondered about brake pad size, shape and form? Most brake pads are shaped as a sector of a circle since brake rotors are circular, but what about slots, grooves or angles that are cut into them? Considering the function of the brakes, a solid surface might seem logical, maximizing contact with the brake rotor, but there’s a surprising amount of engineering that goes into their design and manufacture.

Brake Pad History

In the 18th century, horse-drawn wagons had hand-operated brake levers, braking depended entirely on the strength of the driver. In the 19th century, steam locomotives used various means of braking, hand-operated screws, rotating rods or chains to apply the brakes. Braking friction was provided by wood blocks, which didn’t wear the steel facings of wagon or coach wheels, but the invention of rubber tires rendered wooden brake blocks obsolete.

In 1866, Bertha Benz invented brake linings out of necessity on her first drive in the Benz Patent Motorwagen. Made of shoe leather, these new brake pads were heat-resistant and lasted longer.

In the 20th century, drum brakes and disc brakes would provide braking force to the hub or axle of the vehicle. As the brake pad is designed to convert the kinetic energy of a moving vehicle to heat energy, brake lining materials need to withstand extreme heat. As vehicles got faster, copper, asbestos, cellulose, Kevlar, glass, soft metals, clay and other materials would be used, but what about brake pad shape?

Brake Pad Engineering

Because the braking system in a vehicle is a dynamic system, various forces act on each brake pad, depending on whether the brake caliper is fixed or floating, caliper piston arrangement, whether the brake pad is inboard or outboard, and the overall solidity of the braking components.

• Brake pad surface area depends a lot on how much brake force is needed: Front brakes are usually larger than rear brakes, and sports cars and light trucks usually have bigger brakes than economy cars or smaller vehicles.
• Regarding those angles and grooves, though, engineering brake pads is a little more subtle. Braking generates heat, which can vaporize water or materials in the brake pad. Grooves allow these vapors to escape. Braking also generates vibrations, some of which occur in our hearing range.
• Grooves and chamfers may be cut into brakes pads in specific ways to change the angle of attack of the pad into the rotor and to modify the mass of the brake pad blocks to force those vibrations out of our hearing range.
• Depending on the vehicle, certain angles or grooves may be cut specifically for the inboard pad or outboard pad, so installers need to pay attention to install them correctly. Otherwise, they might be noisy, but braking efficiency shouldn’t be compromised.

Brake pads are indeed more complicated than making them the right shape, but trust that there’s a good reason for those extra manufacturing steps. The next time you’re installing brakes on your car, look for instructions on correct orientation to help your car brake and keep sound at bay.