Blank vs Cross-drilled vs Slotted brake rotors

[jsceash]

I had the pleasure of being at an event with a manufacturers rep. Casting with the hole does 2 things. It reduces machining time, and tool wear, while increasing the edge strength that improves resistance to edge cracking.

The hole idea of cross drilling is to improve heat transfer out of the disc pad and rotor. Heat radiates until it hits an edge and builds up there. The internal fin force air out the hole improving surface cooling. With out the cross drilled holes all you do is cool the core of the rotor. With the cross drilled hole you cool the core and the friction surface. If you've ever watched the thermal imaging of a solid rotor versus a Cross drilled rotor it is impressive how fast the edges of the holes get hot and how fast they cool back down. While the solid one just linger hot and gradually increase overall temperature with repeated braking. I saw a side by side thermal test for 3 minutes. Braking for 5 second cooling for 15 seconds designed to simulate track conditions. the solid rotor was over 150 degrees hotter at the end of 3 minutes with a 22% loose of braking force.

My opinion would be, If the car is a daily drive then use solid rotors. If you track the car at all use drilled or drilled and slotted rotors.

[jsceash]

He also had some impressive test to fail video of, Solid rotors, forged then drilled, cast then drilled, and cast with the holes treated then drilled. Guess which one didn't have a catastrophic failure.

[JFP in PA]

Originally Posted by jsceash

I had the pleasure of being at an event with a manufacturers rep. Casting with the hole does 2 things. It reduces machining time, and tool wear, while increasing the edge strength that improves resistance to edge cracking.

The hole idea of cross drilling is to improve heat transfer out of the disc pad and rotor. Heat radiates until it hits an edge and builds up there. The internal fin force air out the hole improving surface cooling. With out the cross drilled holes all you do is cool the core of the rotor. With the cross drilled hole you cool the core and the friction surface. If you've ever watched the thermal imaging of a solid rotor versus a Cross drilled rotor it is impressive how fast the edges of the holes get hot and how fast they cool back down. While the solid one just linger hot and gradually increase overall temperature with repeated braking. I saw a side by side thermal test for 3 minutes. Braking for 5 second cooling for 15 seconds designed to simulate track conditions. the solid rotor was over 150 degrees hotter at the end of 3 minutes with a 22% loose of braking force.

My opinion would be, If the car is a daily drive then use solid rotors. If you track the car at all use drilled or drilled and slotted rotors.

While drilled (or cast hole) rotors do dissipate heat quicker, their true advantage is in gas control. Disc brake pads are held together by bonding resins which turn into gas vapor under the heat of hard braking, much the way water turns into steam under the same conditions. On a really fast moving race car, the gas generation (from resin or steam during wet sessions) can actually hold the pad off the rotor slightly during braking, reducing the overall braking effort. Holes, slots, or dimples give the gas a pathway to escape, dramatically improving pad contact and braking.

One of the most common comments you get from an owner experiencing drilled or slotted rotors for the first time is how much better the car seems to brake in the rain, when cooling is obviously not an issue.