Yep, that'd be because they are not drilled. Porsche only uses cast holes. Drilled rotors are bad.....very bad!


True, Porsche does cast their stock rotors so the holes don't weaken the molecular integrity of the metal. The new Carrera GT and Enzo use ceramic rotors that are drilled, not cast but that's a whole different world. After-market Zimmermans (which I use for racing) are all drilled with chamfered edges to relieve structural stress. As long as the holes don't cut into the veins of the center venting there won't be any cracking. I have seen cheapo (APC) drilled rotors on Hondas that have cracked, but I think that matches the cracked bondo on their bumpers nicely.