Rotors: Round And Round They GoRotors come large and small, one piece and two piece, drilled, slotted (or both), and vented. What an array of choices. The American psyche is fixated on size and volume. Nothing looks quite so cool on musclecars as an open five-spoke wheel with large-diameter rotors filling the open space. Bigger is always better, right? Obviously, the answer is going to be yes and no, with subtle shades of gray in between. When upgrading rotor or wheel size, rotational inertia and static weight are two things to take into consideration. The larger the rotor, the more surface area for the pads to grab. And more surface area equals lower heat buildup and better heat dissipation.
Whether rotors are one piece or two piece, they can still be thought of as a two-component part. One is the friction disc, which performs all the actual work, and the second is the rotor hat, which joins the friction disc to the wheel hub and spindle. So why are there two-piece and one-piece rotors? Primarily, the reason is weight savings. The advantage of a two-piece rotor is weight savings out on the track. The hats on the two-piece rotors are usually made of an aluminum alloy, while the one-piece rotors are made of the same metal as the friction disc-gray iron. One-piece rotors will generally cost less than a two-piece and can yield the same results. Iron versus aluminum hats-you decide.
Another rotor feature that immediately catches the eye are drilled and slotted rotors. These rotors don't even have to be moving to look mean and aggressive, but what is their true function? When it comes to modern brake systems, they don't make the vehicle stop shorter or cool off the rotors much faster. Is there a use besides looking cool? Back when brake pads used asbestos, they would generate gases and dust during braking. These gases had no avenue of escape, so they would reside between the brake pad and the rotor, causing a spongy feel to the pedal, otherwise know as brake fade. Cross-drilling the rotors gave these gases an escape route.
Today's brake pad formulas create very little gas, making cross-drilling unnecessary. Cross-drilling does have some advantages as well as disadvantages. Cross-drilling a rotor can add a bit more bite to the rotor's surface, which will essentially shave the brake pad's surface, exposing new material. Of course, this can result in reduced pad life. Another slight advantage is possible cooling by bringing more air into the vanes. But cross-drilling can create thermal stress risers, which can speed up rotor cracking.
On the other hand, slotted rotors have slight advantages over cross-drilled rotors. Should a brake pad become glazed, slotted rotors will help shave away the glazed particles and re-expose the pad surface at a slower rate than cross-drilling. Slotting creates a leading edge on the rotor surface, which helps carry away the minute amount of gases that build up between the pad and rotor surface as well as carry away any dust particles that contaminate the rotor's surface. Slotting doesn't have as much of an adverse affect on the rotor as does cross-drilling, just as in cross-drilling there is an increase in pad wear and brake dust accumulating on the wheels. The advantage is more bite for the pads. The choice is yours-reduced pad wear or better-biting pads.
Super Chevy magazine would like to acknowledge help from a few different sources in writing this article: Danny Nix of CPP, Mike Jonas of SSBC, Carl Bush of Wilwood, Ralph Lisena of ECI, and Rich Nossell of Master Power. These companies helped us with tech info and shed some light on braking technology.