These rotors both accomplish the same basic things. Contrary to popular belief, slots and drill holes DO NOT help cool the rotor. They simply allow the brakes to operate properly at a much higher temperature. When pads get hot, the resins and binders that hold the friction material together with do 2 things, either melt or "gas". If they melt, this will act as a lubricant and the brakes won't work, if they gas, the gas will tend to float the pad off the surface of the rotor, so all your pedal pressure goes into compressing this gas rather than forcing the pads against the rotor. Slotted and Crossdrilled rotors allow an escape route for these things. Crossdrilled rotors are mainly beneficial for high end racing where there is a lot of concern for the reduction of unsprung weight. Aside from that and the cosmetic aspect (face it...they look good) there is no reason to go with crossdrilled rotors. Slotted rotor maintain about 95% of the friction surface that the original rotor had while crossdrilling removes much more material leaving only about 70-80% of the original friction surface. A crossdrilled rotor also does not have holes passing evenly over the entire pad as do most slotted rotors, leading to uneven pad and rotor wear because the pad is contacting the rotor for a full 360 degrees at certain points and much less than that at others. Crossdrilled rotors generally wear out pads faster than slotted rotors as well. Another problem with crossdrilled rotors is that they sometimes develop stress cracks around the holes. When the drilling takes place, stress risers are formed because the "web" of the casting is disturbed. Slotted rotors do not have this problem....especially if the slots do not extend past the outer edge of the friction surface. Slotted rotors are better for the street.....Crossdrilled for the track if you are changing rotors after every race and they are not repeatedly heat cycled, which will most likely promote cracking.
