You figure if you are going to drive in sand and silt and crap, you are going to get crap on the disc rotor surface that is going to score it whether you are using standard rotors, slotted, dimpled etc etc. Even with no dimples/slots, when the pads bite on a rotor that has hard particulates on it, you are probably going to get a some scoring
You do it with slotted rotors, then the crap/mud/grit will get trapped in the slots/dimples and really screw up your rotors etc, right?
Maybe These slots and dimples are coated with brake dust just from regular street use and that dust (and the effective anti-rust zinc coatings on most brakes) probably doesn't win any prizes for aiding mud/sand/rock particle-adhesion. That plus high heat born of braking friction which will cause the rotor metal to expand -- again disrupting adhesion or capture of foreign materials -- and the air speed from road-driving probably makes slots and dimples less than hospitable environment for mud/sand/rock particles seeking long-term residency on your after-market rotors.
But if you are using these slotted/dimpled rotors on a non-street-able rig that never gets on the road and is always on the rocks or in mud pits and averaging 1mph (or you'd like to wish that you are
), maybe its a different story. Maybe then you want to get yourself some stock-type rotors.
As for drilled brakes... The way around cracking -- while keeping the potential cooling effect of drilling -- is, apparently, to use over-sized rotors. You'll see big drilled rotors on modern porsche, mercedes cars-- cars designed for 155mph highway cruising in countries that also get snow/ice/rain. If you wanted to do the big, drilled, aftermarket Brembos on a street/trail Jeep, you could probably do it up with no problems. If you hit mud/grit off-road, a little street/highway driving/braking would probably go a long way towards insuring they were cleaned out completely.
