steve g

Darius - I sent you an email.

Thom

Given that you mostly drive your Cup like you stole it readers might be in need of knowing what you actually mean by "normal"

Asarus

By normal, i mean that the cross drilled rotors are expected to crack when you use it hard enought (track use / competition pads). Some people even buy the rotors "pre cracked" for track use because it increases the friction coef a little bit. If this is for a street use, i wouldn't recommand such rotors because it will increase the pads wear (but also increase the brake capabilities when it rains)

NZ951

I have hawk + pads on Zimmerman cross drilled, I have had them about 8 months, the pads eat the rotors, but they look in perfect shape, zero cracks. ANd I brake and drive pretty hard at times. Not a lot of track use though.

Danno

Yeah, it's kinda hard to compare durability & cracking rates between different users and different cars. You'd need to compare for yourself with the car you're driving with the types of driving you do. However, the evidence and experience out there do show more and earlier cracking with holes:





One interesting tidbid I'd like to hear from a metallurgist or manufacturing-specialist, like say... Alan Coleman, is how the Porsche "casted" holes get into the rotor... Meanwhile, it might be good to review the 30-page Altima thread on brake-rotors: Altima Brake Thread (30-pages)

OriginalSterm

thanks Danno for posting that link. I've been searching for it to post up here and to some people I know who are dying to get cross drill rotors.


I do remember reading that it's the sharp edges in the holes that see the high stresses and start to crack. A counter sink would relieve some of that stress, as well as casting the holes properly in the rotor. I believe Porsche has done both from the factory in the past (someone correct me if I'm wrong).

Asarus

Sorry, this is in French but here are some Porsche information about brakes

Thom

Ah ... that legendary sense of humour of computer engineers ...

Asarus

What do you mean ?

My old Mintex M1155 before to put the Pagid Orange (RS4-4) on

Danno

"I do remember reading that it's the sharp edges in the holes that see the high stresses and start to crack."

yeah, it's probably a combination of both a mechanical stress-riser as well as the temperature-gradient in that area.