This plastic lip (red arrows) helps cool the brakes by setting up a vortex in the wheelwel
But rotors can crack under very intense heat. I cracked even my rear rotors before I gave up on drilled rotors. Basically you don't need drilled rotors on the street, and they don't work very well at the track. Got the idea here?
The best explanation of why you don't need drilled brake rotors is found in the advertising for Brembo, which states, "Brembo Sport drilled brake rotors provide excellent stopping power in everyday traffic, as well as more spirited, high performance street and highway driving." It then goes on, "Brembo Sport slotted brake rotors provide excellent stopping power in everyday traffic, as well as high performance street and track driving." Notice that there was no mention of using drilled brake rotors for track use?
Two-Piece Brake Rotors
There are two main reasons for choosing a two-piece rotor over a standard one-piece. The first is weight savings. A two-piece brake rotor's center aluminum hat reduces the overall weight by an average of 3 pounds versus a one-piece, cast-iron rotor.
Remember how I said earlier that lightweight rotors are generally cheap junk? Well, with a two-piece rotor you can have light weight and strength at the same time. The actual rotor can be substantial enough to dissipate heat properly, while the aluminum hat section saves weight. This is the best of both worlds.
This is a front brake on a C3 Corvette vintage racer. Even though the rotor is much smalle
The other big advantage of the two-piece rotor is that it's easier to vent air through the rotor's center. The ideal brake duct is one that pushes air into the center of the brake rotor, thus allowing the heated air to exit through the vanes. Two-piece rotors are ideal for this ducting and cooling.
Two-piece rotors can be very expensive when you first install them. Just the rotor alone for my C4 is $183.54. The hat section is going to be an additional cost, but only once. This means that a one-piece brake rotor is cheaper, but not by a lot. I might add that I've never cracked a Wilwood brake rotor, but then again I've never cracked a NAPA premium rotor. I have, though, broken just about everything else.
A lot people also prefer two-piece rotors for cosmetic reasons. The black aluminum center hat bolted to the rotor ring gives the brakes an aggressive, race look. Just be prepared to pay the price.
No one talks about brake rotor prep, but it's a really big deal. You can't just take a brand new rotor out of the box and throw it at the car. Even worse is to take a used brake rotor and install new brake pads without any rotor preparation. This is just asking for trouble. You run a huge risk of brake squeal, and you're not getting the maximum effectiveness out of the new brake pads.
I sand brake rotors all the time. Any number of people will tell you it's unnecessary, but I've installed thousands of brakes on a wide variety of cars, and I can count the number of noise problems I've had on one hand.
This is a carbon fiber brake rotor on a Pratt and Miller GT1 Corvette. This is the state o
Most suppliers of bench lathes and on-car lathes say sanding after turning isn't necessary as long as proper feed rates and sharp lathe bits are used. The finish should be within specifications and cause no problems. Proponents of sanding claim that sanding improves the finish by making rotors smoother. Sanding knocks off the sharp peaks as well as torn and folded metal left on the surface by the lathe bits. Sanding may improve the surface finish 2 to 5 microinches. This will give you better pedal feel, quicker pad seating, and improved overall brake performance.
Rotors can be sanded in various ways. One is to apply a non-directional finish with 80- to 120-grit sandpaper on a flat sanding block. Hold a pair of sanding blocks against the brake rotor for about 60 seconds while the rotor is turning at normal speed on the lathe (assuming you have a machine for turning brake rotors in your home garage).
For the rest of us, the most common method is to use an abrasive pad on a drill. This technique is risky because it's difficult to do an even job, and metal buildup on the pad may actually make the surface rougher unless a fresh sanding pad is used for each side of the rotor. If you do sand, do it carefully, evenly, and remember that you're not trying to remove metal. A minute or less on each side should be enough. You'll see the scratches develop as you use the sanding disc. You really don't want to remove any material; just simply scratch the surface.
Sanding becomes even more critical when installing new brake pads on old rotors. The surface of the brake rotor is coated with the old pad material. When you install new brake pads, the new friction material won't contact the rotor but will make contact with the old pad material. You want your new pad material to contact the steel of the brake rotor. Sanding the rotor surface assures that this will happen.