Yup. I know at one point during a national event my brakes were smoking when I came across the finish line - at an autocross!

 

:chuckles:



Anyway, the heat dissipation properties of cross-drilling really aren't of much use to the general track enthusiast who's pad choice generally calls for an increase (or at least a wider range) of opperating temperature. The pads we use actually usually work best with the ammount of heat generated by blank rotors. In most practical situations, I can't see the decreased friction surface being worth the (often unnecesary) lower opperating temperature. :dunno:

 

ahh, well if the rotors stay hot and dont cool down, they will warp. Even with less fricton surface, the disc's angular velocity is usually high enough in order generate the heat required in race applications. In return the disc's will cool down when not in use if they are cross drilled. Under situations where there is a lot of stop and go, with blank rotors, the rotors will heat up more and more if not enough of a cooling period is allowed between use. This will lead to failure, on the part of the rotor "warpage or cracks" but the pads can handle it, depending what the pads are made of.

Nader

 

Sorry no. Rotors can stay hot as long as they want they will not warp from heat soak. They will warp if you do not cool them evenly. Sort of like what happens with you heat a glass cup and cool down one side quicker than the other - it will warp or shatter.

Most guys that are new to brake dynamics don't know this and after a track session or hard driving will just park their car with the e-brake on or with the brake pedal engaged causing uneven heat dissipation. The pads act as a blanket while the rest of the exposed rotor cools down quicker.

Cross drilled are more prone to cracking then any other rotor. Just show up to a driving school with aftermarket cross drilled rotors and see what happens at tech. The only cars allowed with cross drilled rotors are factory issued ones like Porsche or Ferrari (and even with those cars I've heard stories of factory cross drilled rotors cracking too). What happens with a cross drilled rotor is that the heat expands the rotors pass the point of the holes drilled into the rotor. The holes cannot expand as much and crack due to the heat expansion.

Even after a full weekend of an HPDE with NASA (2 days 4 twenty minute sessions) my brembo blanks did not warp with AEM pads, but I did get brake fluid boiling.

 

i agree with you, that rotors will warp if they dont cool evenly, however they will also warp if they attain exsesivly high temperatures. Temperatures that cross drilled rotors wont reach because they are cross drilled and that blank rotors will. Just like when they make steel, they heat the iron to mold it, iron changes forms easily when heated at extremly high temperatures, same for brakes and as i was saying earlier I have many friends and clients that have warped BREMBOS because they use a higher alloy steel which stay hotter longer. And if you brake hard when the brakes are hot and the metal is softer, you will warp the rotors. garanteed.

Nader

 

yes iron will melt if you heat it high enough but you'll never reach those temperatures even in a full on race car.

sorry I'm calling BS

 

i never said they would melt. Anyway, there are many people on this board that know what they are talking about and then there are others that dont, they just repeat what others say, because they dont know what they are talking about.
I for one, know what i am talking about. Go and tell any mechanic or automotive engineer that rotors only get warped when you put the hand brake on when your brakes are hot, Watch them die of laughter. last time i checked, i didnt have a parking brake system that locked up my front brakes, yet they got warped one time, I WONDER WHY!!?!?! hmmmmmmm. I think i have to go back to school and retake my mechanics of materials courses.

Nader

 

oh ya if brakes never reached such high temperatures then they would never ever warp! Under those hot conditions the metal expands my friend, and if they get too hot the metal becomes softer and if you brake hard, the normal stress that is applied by the pads on the rotor will cause the rotor to deform.

thats my last comment on this topic.
enjoy

Nader

 

You sir have alot of nerve coming on here telling people they don't know what they are talking about while you blatantly state that you know what you are talking about. You have an engineering degree, congrats. Bring your :blah: to the track, see which 'theory' is correct.

I hope so.

 

Engineering degree ....wow. So that makes you more knowlegable in cars and performance parts?

You definately have never seen track time or experienced it. Go join NASA or SCCA and run a beginner's lesson and see what EXPERIENCED drivers and instructors say. Go learn the limits of your car. Until then, I dont think you have any reference or proof of your knowledge in parts and performance.


Later Nader.