When should brake rotors be turned or replaced?

Brake rotors should be turned or replaced when they have excessive runout. Runout refers to the amount by which the rotor deviates from a perfectly flat surface when it is rotated. Excessive runout can lead to uneven brake pad wear and vibrations during braking, which negatively impacts the vehicle's braking performance and safety. If the runout exceeds manufacturer specifications, it can cause the brakes to pulsate or grab, leading to a less effective braking action.

While other factors such as a shiny appearance, minimum thickness, and squeaking noises can indicate issues with brake rotors or pads, they do not directly determine the necessity for turning or replacing the rotors like excessive runout does. A shiny surface may occur due to glazing from overheating but doesn't inherently indicate a need for servicing. Similarly, rotors that are within the minimum thickness specification are still usable, and a squeaking noise can result from worn brake pads, debris, or other issues not directly tied to rotor condition. Thus, checking for excessive runout is crucial for ensuring brake system integrity and performance.