Ron

I read, not on Rennlist, where someone said that cross drilled rotors reduce braking efficiency. That's not accurate is it?

Monique

If you start out with identical disks and drill one set, then you have reduced the material needed to absorb the heat. However, cross drilled brakes cool much quicker than their un drilled counterparts.

Bottom line? The dude is talking through his hat!

garychios

Its a known fact the slotted is much more efficient that x-drilled. Ask any brake company and the test results show shorter distances, less cracking and when it comes to braking, the weight is not an issue.

Bruce SEA 993

The holes or slots let the gasses escape that are genereated during the stop.

GrantG

I think this is less of an issue with modern pads (less outgassing). I think slots and holes help with wet conditions and helps keep pads clean. Cracking is certainly more prevalent with drilled rotors than grooved...

chris walrod

As Bruce said.

Yes, there is some reduction in thermal capacity, but the benefits outway. Slotted rotors are preferred. Its not desired to put holes in any stressed component as its then weakened.

Wish there were slotted rotors available without having to purchase a complete brake 'kit'..

Mark in Baltimore

I have been longing for solid or slotted rotors so I can avoid or, at least, slow down the rotor cracking which originates from the vent holes.

Greg Fishman

On big point is that the Porsche rotors are not drilled. The holes are cast in them, big difference.

garychios

Greg, never heard this. I thought Brembo did the rotors for Porsche. I know brembo drills the upgrades.

GrantG

That may be true, but they still crack. The cast ones probably last longer before cracking though...

Rob 97 993c2

im confused, if the above is true, why did porsche put holes in the big red rotors? Are smooth rotors better?

GrantG

Rotors with holes only crack under extreme track use. Rotors with holes are better than flat rotors for street use, since they offer better contol of gasses and work better in wet conditions. For dry track conditions, flat rotors are better than ones with holes (less cracking), but grooved rotors seem to be the best for all purposes...

Harvey Yancey

And unfortunately there does not seem to be any slotted rotors for our cars anywhere out there ...

Dan993

Nearly all OEM 'drilled rotors' have the holes cast in. These parts are designed (vane design, metallurgy, diameter, thickness, etc.) with holes in mind. The casting process includes the 'holes' which are revealed in the final machining process.

It is very true that Brembo and others (many, many others) take factory rotors and drill them for 'sport rotor' applications. In all these cases, the rotors are not designed for this additional machine work. To top it off, they almost always are used in agressive driving (track, auto-cross, canyon driving, So Cal freeways) and end up cracking. The rotors' ability to go repeatedly through the heat cycle without failure is compromised. It matters very little whether the rotor is manufactured by Brembo, Balo, Zimmerman, ATE (acutally made in Italy by Pilenga) or various Asian manufacturers. Mettalurgy of these aftermarket rotors is all about the same, so results are the same.

But they look cool.

Slotting allows the venting of pad outgassing and some cooling, resulting in less fade. And no cracking.

Steve Weiner-Rennsport Systems

Dan993 is right on,..... Great post.

I'd add that "drilled" rotors, while more crack prone, do offer better "bite" than slotted ones and may be preferred in some applications. This subject is definitely not, a one-size-fits-all sort of thing,.......

Everyone's preferences and needs are different and there are many kinds of solutions that should not be abstractly ruled out.

Slotted rotors do crack as well, just not as often and the bottom line here is truly managing & controlling the heat. Slotted rotors are available, just not at the cost that most people are willing to pay for them. Professional grade brake components are decidedly not inexpensive,...