Ceramic Brake Pads Vs. Semi-Metallicby Dennis Hartman
The braking system is one of the most important parts of an automobile. Brakes are integral to vehicle safety as well as performance. Like most vehicle systems, brakes also require occasional service, including the replacement of brake pads, which wear down with use. While most new cars come with semi-metallic brake pads, other types of pads are available from aftermarket auto manufacturers that may work better for certain drivers.
For decades few decisions were made when choosing replacement brake pads. Semi-metallic and asbestos-based pads were used interchangeably and performed in a similar way. As health concerns led to a decline in the use of asbestos pads, newer materials, including ceramic, were used instead. The appearance of ceramic brake pads as a common aftermarket option began in the 1990s. Today several different types of ceramic pads are available, along with a range of semi-metallic and other options.
Semi-metallic brake pads are composed of various metal bits, along with a bonding material to hold the pieces together and give the brake pad its structure. The metals used can include anything from steel wool to bits of metal wire and iron dust. Graphite and copper are also commonly used. In general, semi-metallic pads contain between 30 and 65 percent metal. So-called low-metallic pads are similar but use less metal in their construction. Ceramic brake pads are made mostly of ceramic fibers and may also contain a small amount of metal.
Ceramic and semi-metallic brake pads are used in the same way once inserted into a car's braking system. Brake pads are used on disc brakes, which use the pads to squeeze a spinning disc rotor. The pads are attached to a caliper that closes as the brake pedal is depressed inside the car. The pads produce friction and intense heat by rubbing against the spinning disc, thus slowing or stopping the car. Over time the pads wear down and become brake dust which coats the inside of the wheel or is discharged onto the road. Once they wear down enough, the pads must be replaced.
Ceramic and semi-metallic brake pads have certain advantages over other types of pads. Semi-metallic pads are inexpensive and provide excellent transfer of heat away from the rotor. This helps prevent against warping of the rotor, which can occur when the rotor is overheated. In addition, semi-metallic brake pads are hard and wear down slowly. Ceramic brake pads are softer and so put less wear on the rotor's surface. They are also quiet and are good at producing smooth friction for consistent stopping.
Both types of brake pads also have certain disadvantages. Ceramic pads are more expensive and, because they are so soft, wear down more quickly. They also subject the rotor to more heat. Semi-metallic pads may wear down the rotor itself more quickly, requiring it to eventually be replaced. They can also be noisy, since they contain metal shards that will come into contact with the rotor once they are exposed on the surface of the brake pad. This will produce noise until either the metal shard in the pad, or the rotor itself, wears down sufficiently.
- photo_camera Image by Flickr.com, courtesy of Nam Nguyen