Why do automotive brake rotors warp?

Braking systems are comprised of various components, including rotors. Rotors are large metal discs that can be seen behind the wheels of the car. Rotors can sometimes appear to warp, and many drivers may question why this occurs or if this is a significant problem.

Rotors cannot really warp. Automotive experts note that rotors are metal discs that are cast under extreme heat conditions. It would take a similar application of heat by the braking system for rotors to actually bend, which is impossible. Other factors make rotors appear to be warped, so describing such rotors as “warped” is an easy way to explain the problem to vehicle owners.

For brakes to work correctly, brake pads must be applied squarely and evenly against the rotor. But friction can cause some brake pad materials to form residue on certain areas of the rotor, eventually contributing to uneven rotor surface levels. Some spots become thicker, while others may thin out.

Drivers’ own habits, including their braking tendencies, can contribute to uneven rotors. Riding the brakes for prolonged periods of time can cause hot brake pads to “paint” the rotors. So constant braking should be avoided.

Drivers also can shift into a lower gear when driving downhill so that prolonged breaking is unnecessary. Also, avoiding frequent hard breaking may help. People who live in an area where they’re hard on the brakes either because of hilly terrain or traffic may find such environments can take a toll on the performance of their vehicles’ brake systems.

Brake system issues, such as front brakes having to work harder than rear brakes, or over-torquing when wheels are installed, also may cause rotors to warp. New pads and brake pads need to be fitted correctly and properly “bedded.” Bedding is the initial transfer of friction material from pad to the disc to form a smooth, uniform layer. Break-in instructions should be included with new brake installation.

Warped rotors can cause symptoms such as squeaky sounds and lead to jittery feelings in the car when brakes are applied. Such rotors also can cause the vehicle to vibrate when coming to a stop.

If warped rotors seem to be an issue, mechanics may be able to put thicker rotors into a lathe to smooth out the residue and restore an even surface — but the problem can come back. It is usually best to replace rotors if they are causing severe vibrations or issues when braking.

For the do-it-yourselfer the experienced staff members at automotive supply stores such as, Advanced Auto Parts, are a valuable resource for getting people access to the parts and tools they need to get the job done.

THE STAR NEWS