What is the final word on drilled and slotted rotors?

[Nicks67GTO]

Is it just a bling thing or is there real function? Iv'e read that drilled and slotted rotors can reduce operating temps by 180*. Iv'e also read that drilled and slotted rotors can crack under normal street use and are prone to it under hard track use, most of the issues arise from the drilled areas. Whats the reality here for most street cars that auto X occasionally?

I'm trying to match come C6 Z51 front rotors with some LS1 rear rotors before I pull the trigger on my Kore3 kit. I'm finding Powerstop drilled, slotted and zinc washed rotors that should match but I don't want them if they're going to go to warp/crack in a hurry.

[SLO_Z28]

It has more to do with the rotor manufacturer than anything else. 17 years later my drilled and slotted hub/rotor OE replacment units are .070 over machine too specs with no cracking. For your setup a set of stoptech rotors from tire rack would work extremely well.

The slotting stops gas build up and improves pedal feel, and the drilling reduces weight. It doesnt help much with cooling but it is benefitial performance wise.

[nine lives johnny]

Slotted work, they remove the intensely heated particles that are created in the braking process.
If you look to any professional team that does testing and they will all run a form of slotted rotor.

Drilled does not work. it's all for looks. like the hood scoop on a 2002 mustang. it does remove allot of material from the rotor itself and will decrease performance.
If you look to any professional team that does testing they will not have drilled rotors

I know more about brakes than any one man should know. i'm a brake guy. if you got more questions let me know.

[parsonsj]

Drilled does not work. it's all for looks. like the hood scoop on a 2002 mustang. it does remove allot of material from the rotor itself and will decrease performance.
If you look to any professional team that does testing they will not have drilled rotorsWord.

On a personal note, my Z06 came to me with slotted and drilled Brembo monster brakes 14.5" front rotors, 14" rears. After multiple track days and 3 set of pads, all 4 rotors have cracks from each drilled hole. Some of the cracks are starting to meet each other, so it's new rotor time. The new rotors won't be drilled!

[79-TA]

Whether or not a rotor will fail due to cracking has more to do with the metallurgy of the rotor. James described it well. Cross-drilling takes a bit to explain.

Cross-drilled rotors were originally a solution to the problem of severe off-gassing of brake pads. You'll see some brake manufacturers still advertising them this way. Some of the first friction materials used for disc brakes contained volatile materials that would create significant volumes of gases that would effectively lubricate the pad on the rotor's friction surface. Modern pad materials have almost completely eliminated this problem. Cross-drilling now serves to either create aesthetic appeal or to reduce thermal mass. The second purpose is a bit confusing as increasing thermal mass is usually the goal of upgrading to larger brakes. You could think of it as dialing in the amount of thermal mass if you knew you had too much.

Cross-drilling creates liabilities in terms of rotor strength. The sharp edges act as thermal and physical stress risers. Even if the holes are cast in, a plain, slotted, or dimpled rotor would still be stronger and more resistant to cracking. The drilling is an extra cost and step in manufacturing, creating additional chances for mishandling and human error. A drilled hole in a rotor must not intersect the vanes. The vanes are all that hold the back friction surface of the rotor to the rest of the part, so weakening this connection is not acceptable. Also, drilled holes must not be too close to the edge of the friction surface. One positive spin to put on the cracking liability is that the holes will most likely crack first, helping you inspect the rotor more quickly . . .

The next step from drilled holes are dimples. Filled in with brake dust, they create the appearance of holes, but do not create the same cracking liability. They have the same cleaning or anti-glazing effect that drilled holes would on the friction material.

Safer and more conservative still would be slots. The longer length creates a leading edge that covers the pad more uniformly. Slotted patterns can be minimalist to extreme, but almost always have less combined leading edge length than a drilled pattern. There are a couple of design flaws that can affect slots. Slots must not continue to the edge of the rotor or be too close to the edge. They should also be oriented as to not create weak spots. This might mean offsetting the slots on one side from the other or running the slots opposite to the direction of the internal vanes.

The leading edge of a hole, dimple, or slot, serves to "clean" the pad by shaving off part of the friction. This can eliminate friction that has become too hot and changed friction characteristics while adding "bite." ("Bite" is a completely relative and subjective term use to describe how quickly a pad builds friction once brake pressure has been applied.) Leading edges of disc features can help maintain more consistent pad performance with this cleaning action. More leading edges will equate to more shaving and accelerated pad wear. The useful effect of "cleaning" the pad is accomplished by the simplest of slotting patterns, so anything very fancy is usually overkill. Some more elaborate patterns will try to use concentrated leading edges on the inner diameter of the friction surface. This increases pad wear at the cooler, slower moving portion of the disc in an attempt to prevent radial pad taper.

Now for cooling. Do cross-drilled rotors improve cooling? No. One might think the increased surface area available for convection cooling (air flow) would help. However, the primary method of heat transfer in a braking system, even at low temperatures, is radiation. That's right, light emissions cool the rotor even more than air flow. The rotor would cool better with the flat surface radiating light away from the brake system rather than a void.

Drilled holes can also have interesting effects on the air flow through the vanes of vented rotors, but that leads into a discussion that's more about vane design.

[Damn True]

As complete an explanation as I've read.

[Nicks67GTO]

All of this is good info. Though I do find it strange that GM would drill the stock C6 Z51 rotors knowing all of this? I wonder why they did that? All of that said, it sounds like slotting is great and very useful, drilling is bad and nothing but bling and a slight weight savings. Thanks guys! Ill post my next question in a new thread.

[Damn True]

Because the overwhelming majority of those Vettes will never see the track and most knuckleheads think they look super racy. The ones that do see the track will have the rotors replaced with quality items in short order.

[minendrews68]

Yep, aesthetics only I'm thinking. Besides too many people have seen them and without knowing, think they're cool so they must be good.


Because the overwhelming majority of those Vettes will never see the track and most knuckleheads think they look super racy. The ones that do see the track will have the rotors replaced with quality items in short order.