Originally Posted by HotWS6

I know a lot of people that have slotted/drilled rotors...are they that prone to cracking? Why would they make them?

Originally Posted by Wilwood

Why are some rotors drilled or slotted?
Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.

Originally Posted by Baer

What are the benefits to cross-drilling, slotting, and zinc-washing my rotors?
In years past, cross-drilling and/or slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as "green pad fade" or "outgassing". When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting! However, with today´s race pad technology, “outgassing” is no longer much of a concern. When shopping for races pads, or even ultra high performance road pads, look for the phrases, "dynamic surface treatment", "race ready", and/or, "pre-burnished". When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with “outgassing”. Ironically more pedestrian pads used on most streetcars will still exhibit “outgassing”, but only when used at temperatures normally only encountered on the racetrack. Although cross-drilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs. Cross-drilling offers the greatest gas relief pathway, but creates potential "stress risers" from which cracks can occur. Baer´s rotors are cast with cross-drilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings.