Cooked Brakes: Excessive heat and why it’s detrimental.
Heat management is a massive contributor to rotor wear and outright braking performance. Each time the brakes are applied, the friction between the pad rubbing against the rotor generates incredible amounts of heat. Aggressive driving, hauling a trailer or heavy loads, and steep incline/decline driving can all cause brake temperatures to soar.
Naturally, heat is a huge killer of brakes, physically and from a performance standpoint. At mild operating temperatures (under 200oC), street brake pads provide the its effective friction levels. However, at higher temperatures, the pads themselves can transfer a thin layer of material onto the surface of the rotor. As the rotor then begins to heat up, this abrasive friction transforms purely to adherent friction. This type of friction is how most racing pads are designed work and also explains why they generally don’t stop well under cold conditions. Keep in mind that brakes are a general consumable for a race car, and they are maintained at a high, yet non-excessive temperature via supplemental cooling with ducting.
On your street car, once the rotors continue to get excessively hot, material from the pad liquefy and ‘glaze’ the surface of the rotor, compromising stopping effectiveness. Worse yet, as the pads rub on the now-glazed surface, they will get even hotter until the heat localises to just one area of the rotor. At temperatures around 620oC this effectively changes the cell structure of the metal into hard brittle patches (known as cementite). These spots fail to wear down like the regular iron surrounding the patches, so they become raised and starts causing annoying brake pulsation or shudder.
The braking performance of the car will be negatively affected once brake fade via high temperature sets in. While this loss of stopping power can be caused by the aforementioned friction fade, mechanical fade or fluid fade can also be faulted. Brake fade can be significantly reduced by appropriate equipment and materials design, quality brake selection, as well as good cooling.
Vented, drilled and slotted rotors like those which DBA manufacture are the key to controlling the dissipation of all that thermal energy. As the rotor is effectively a giant heat sink, the number, spacing and shape of the cooling fins in vented rotors is essential in venting built up heat, with some designs are more efficient than others. Drilled rotors also assists in keep the temp’ below the point where heat spots begin to form, while also helping to prevent pad glazing.
High temperatures are not ideal but sustained high temperatures are highly detrimental to your braking system. Rotors and pads with temporarily raised brake temperatures will return to normal functioning when allowed to cool naturally. Permanent rotor damage can occur with continuous high temperature abuse – to the point where warped rotors are cannot machined flat anymore, due to deep heat patches. It is also important after a ‘hot stop’ not to clamp down on the brakes. This can deposit friction from the pad onto the hot rotor in just one spot, elevating the friction effect solely in that area and beginning the cycle of heat spots and uneven wear.