Chances are, your rotors are “warped” and due for replacement if you are experiencing any of following symptoms during breaking:
• Pulsation of the brake pedal
• Vibration of the steering wheel
• Throbbing noise from the rotors and pads
The severity of these symptoms may vary, being best noticed during breaking on a highway at higher speeds.
The common term to describe the damage to rotors causing these issues is “warping”. Note, that the damaged rotor may not be physically warped. Instead, it is more likely to be cracked, broken, or unevenly worn, causing the fluctuations of braking force and cyclic side loading of brake calipers. In turn, this causes your car to shake and vibrate during braking.
In many cases the damage to the rotor is unnoticeable by a simple visual inspection. In a severe case you may see significant rust pits and gauges with uneven surface discoloration. However, this will be a good enough reason in itself to change an old rotor. So how would you otherwise inspect a rotor for warping? The inspection is not straight forward, and involves precise measuring of Lateral Runout - the difference between the high and low spots on the rotor friction surface. For example, AllRotors Premium Precision-Ground rotors have the runout and thickness variation of max. 10 microns (0.01mm), while competitor rotors are over 20 microns. Higher runout values can be noticeable and could generate complaints. The measurement of these small variations contentiously over an entire surface of the rotor requires special equipment and skills, and the proper diagnostics may cost more than your average set of rotors and pads. As such, most mechanics do not test the rotors beyond the visual inspection, and simply replace front and then rear rotors and pads to tackle the problem. The rotors are replaced in pairs (both front rotors and/or both rear rotors), and it is not recommended to replace only one rotor.