There are plenty of myths concerning brake rotors, some of them even making enough sense to hold an arguable position. However, for a self-respecting driver or car owner, few things matter more than figuring out what works, and replacing or fixing what does not. For your own sake, it is best to debunk the following falsehoods at the earliest.
Heat Dictates the Minimum Thickness Specifications of a Rotor
Technically termed discard, this factor is influenced primarily by the caliper piston's travel in the event that the pads have experienced wear up to the back plates. If your brake pads are especially worn, the piston may begin leaking, and could even come undone from the bore, resulting in complete system failure. However, heat and warping are totally unrelated to the thickness specifications.
Wet Brake Rotors Raise Stopping Distances
This is only partially true, in that it applies exclusively to drum brakes. However, since most cars use the disc brake system these days, you probably do not want to believe this point outright when someone makes it to you. In disc brakes, the spinning rotor throws off any water thanks to its high centrifugal force, which means wetness here is not a concern big enough to affect stopping distance.
Brake Rotors Can Warp
No, they cannot. What people call “warping” requires two things to happen first, which are technically termed as brake torque variation and disc thickness variation. The former involves a torque variation being created across the surface of the rotor, caused often by its make. On the other hand, disc thickness variation is just a noticeable difference in thickness between any two parts of the rotor disc.
All Rotors are Created Equal
Even if a rotor is a perfect fit for a vehicle, there is always the possibility that it can prove inappropriate. Many low-quality rotors carry structural and metallurgical issues, which while good on your wallet, would reduce safety by quite a few notches. When the time comes that you have to stop the car at high speeds, the difference between this and something of better quality would become easier to understand.
New Rotors Need Machining
New rotors are supposed to come completely finished to specifications, right out of the box. If you need a clean-up cut, then your supplier has probably scammed you into buying a sub-standard product. Not only is machining a new rotor needless, but it is also bad for it and could shorten its life.