Brake Rotors

Brake rotors, or just rotors, are the discs that rotate with the wheel and provide a surface for the brake pads to apply friction to. They can be made using a wide variety of materials and manufacturing methods depending on the system they are used in, mostly dependent on the brake pad material.

Materials

The selection of material is highly dependent on the engineer's design goals for rotor operating temperature, pad-rotor coefficient of friction, material strength and other properties.Rotors can be constructed using the following materials:

• Steels of low to high carbon%
  
• Chromoly (4130 Steel) or other alloys
• Cast Iron
• Aluminum Alloys
• Carbon ceramic

Typically pad-rotor coefficients of friction and ideal pairings will be specified by the brake pad manufacturer, but this can also be physically tested and verified in-house by teams who have the resources to do so.

Post-Processing

Lightening

A common practice is the drilling of holes or slots into or all the way through the rotor. This practice has several effects on brake performance:

• Decreasing the area of contact between the pad and rotor, thus impeding the flow of heat into the rotor but also venting heat off the pad
• Adds a shaving effect to keep the pad surface clean
• Increases rotor temperatures through reduction of mass
• Decreases rotational inertia of system, wheel becomes easier to roll

A common misconception among designers is that doing this increases cooling effects on the brake rotor by increasing it's surface area. While drilling holes in the rotor does increase surface area, unless there is some form of air actively being guided through those holes either by brake/wheel ducts or winglets, there is no significant airflow through the holes of the rotor. Reducing the mass reduces the overall thermal capacity of the rotor, which leads to an increase in temperature during use. However, there are ways of increasing airflow through such slots and holes. For example, a wheel center that is designed to act as a propeller, sucking air into the wheel assembly and sending it through the rotor can change the direction of airflow from across the rotor's surface to through it's holes and slots, making the process more effective. This can also be done by adding the holes and slots at an angle, creating a slight suction effect as the disc rotates.

Venting

Vented rotors are rotors with fins in between either contact surface that allow air to pass inside the rotor itself. The way air travels through the rotor is dependent on the configuration of the fins inside.