Which of the following measurements should be performed when checking disc rotors?

To properly assess the condition of disc rotors, it is essential to measure both radial runout and thickness variation. Radial runout refers to the variation in the rotor's distance from a fixed point, which can impact the braking performance and contribute to vibration during braking. On the other hand, thickness variation assesses the uniformity of the rotor's thickness around its circumference. If the rotor's thickness is inconsistent, it can lead to uneven wear, reduced braking efficiency, and increased chance of rotor warping.

By measuring these two parameters, technicians can effectively determine if the rotor is suitable for continued use or if resurfacing or replacement is necessary. These measurements provide crucial information to ensure safe and efficient vehicle operation, particularly concerning braking systems.