To drill or not to drill...

#1

I am almost done with my spec e30, and have done a bunch of HPDEs with the car. My last brake setup was Hawk HP+ pads and Zimmerman cross drilled rotors. I ended up cracking the rotors…I am now replacing my brakes and am going with the Hawk pads again, as I didn’t have any fade problem, and they worked great…I have decided to try regular rotors this time, but my friend that races vintage cars keeps telling me to drill my own rotors on the drill press, using the same pattern as the previous rotors (but making sure to bevel sp? them correctly.). Should I? What brake setup do most of you guys run? Is it a mistake to run regular non drilled rotors?

#2

if you have a look at the Tire Rack site, they actually discourage the use of slotted or drilled rotors for racing - I suspect if they thought they could sell them, they would, but they don’t. Home drilling rotors would be a HUGE mistake in my mind.
cheers,
bruce

#3

I agree with Bruce. I would definitely not drill my own rotors. I have had Zimmerman drilled rotors on a M3 track car and they cracked terribly. The difference in performance gained by using drilled or slotted rotors is not worth the extra costs. Just get oem blank rotors and save your money for brake pads and tires.

Some of the SE30 guys use the "frozen" rotors and swear that they last longer but they cost about twice as much as standard blanks.

#4

Ditto what Bruce and Ken advised. If fact, the slotted rotors crack easily as well. I don’t know of anyone running anything but stock rotors, some frozen. The frozen rotors are great and we bought one set last year. They lasted twice as long, but they are not cheap.
Ed

#5

Use plain rotors, they work fine. Keep a spare set just in case you crack them, but they should hold up. Ducting and proper cool down are going to help longevity.

#6

Drilling your own rotors? That’s "vintage" indeed. You’d be braver than me, that’s for sure.

Unfortunately Bimmerforums is down for maintenace as I write this, but I’m pretty sure there’s tons of discussion about this topic. If I remember correctly, cross drilled rotors that you buy are cast with the holes in them, not cast and then actually drilled. There is a difference in the strength of the rotor.

As said above, on the E30’s, vented rotors with ducting is as good as you’re going to get. Even those will crack.

In case you do end up drilling your own holes, MAKE SURE you counter sink those holes or else you will eat a set of pads very, very fast.

#7

Drill your own rotors? He must not like you very much :ohmy: . That is the dumbest thing I have ever heard. Cross drilled rotors suck unless they are probably cast like porsche rotors. Go with stock. And upgrade those brake pads while you’re at it, HP+ are not going to cut it in a race environment. You can keep the plus on the rear if you want but put something like an HT-10 on the front.

#8

Cross-drilled rotors are purely for the bling factor. I’ve never seen them on any professional race car and only seen a few with slotted rotors.

Cross-drilling reduces the mass of the rotor, which is bad from a thermal standpoint. And the holes reduce swept are, also bad. And the holes are stress concentrators under thermal cycling. Think of the holes as an initial crack of large radius.

Plain rotors are what you want.

#9

Plain rotors, Brembo & Zimmerman blanks it’s what I use in my track cars.
I would get DBA slotted rotors since I’ve used and abused them off-roading, and they have a special vane design to improve cooling, that’s a fact from my own experience off-roading.
Tire rack offers the 4000 and 5000, basically the same, just the first is one piece, and the second two piece.
I’ve used frozen rotors, and wasn’t very impressed, had to replaced them in the same period as a regular rotor.

#10

Elephant4 wrote:

From the information I have gathered from Brembo, OEM BMW parts, and a few other sources, all discs are drilled. Simply put, the cost to include the “holes” in the casting would be extremely expensive to get quality levels at the same as drilling can allow. But it’s just hard to find what brands do their research and what do not since the end results look very similar.

Most of the confusion comes from the way that some of the technical product brochures or part descriptions aren’t using the best choice of words nor do they stick to the same terms.

But I definitely agree with you. Drilling your own rotors is a very bad idea. Better brake pads would make a much bigger difference.