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Brake Rotors: slotted versus drilled

Posted by Steven R. Rochlin (R) on August 20, 2004 at 21:09:12

Ahh, off the General forum and onto a more proper venue:

After MUCH research and chatting with various engineers (including a main tech from Brembo, a guy from the Prodrive race team, and others)...

Here are the basics:

We are talking about relatively lightweight floating rotors with aluminum caps (think Brembo GT series, though this still applies to Tarox and the like). We are also (generally) discussing more race/inspired driving versus a 'grocery getter.' Lastly, your driving style (or lack thereof) and brake pads can make a HUGE difference as to how much heat and grip your brakes may generate. Lastly, naturally you would want to use proper race brake fluid (Motul 600 or the like) due to a higher boiling point (to avoid 'cooking' the brakes... also called brake fade).

Like in audio, a single components does not work alone, it is within A SYSTEM and as such, one needs to account for both front and rear systems on a car. Think Brembo GT series brake rotors, though this still applies to Tarox and the like.

DRILLED: Has LESS metal material and therefor has less metal to dissipate heat. Also, drilled can play 'connect the dots' (read: crack). Will avoid discussing rotor warping.

Keep in mind many companies just drill holes in a solid rotor and the holes ARE NOT part of the manufacturing process. This can cause metal irregularities and 'connect the dots.' Yes, the holes may help during rain to rid water float, yet the same can be said for slotted (and slotted is more effective here due to the wiping effect of the angled slots). And if you feel drilling saves weight on the rotors, it does, but it also LOWERS the amount of metal on the rotor that stops the car. As i recall, solid rotor is 100% material touching the pad, slotted is about 92% and drilled is 85%. More metal equals more pad grip and lower stopping distances.

SLOTTED: More material than drilled means better heat dissipation. During wet driving the slots have a better wiping away of water versus drilled. Slots also wipe the pads to keep the pad surface clean.

Am avoiding the whole brake pad out gassing issue as this MIGHT happen DURING bedding in, yet once the pads are bedded this is really a nearly moot point on modern high-performance pads.

If you are just Joe Driver with the sporty Grocery Getter, a stock setup is fine. If you enjoy more inspired driving in the streets, aftermarket slotted can help but MAKE SURE you match the front and rear as there is a balance (front/rear bias) engineered into your car's brake system and if you do not know what you are doing, altering this balance can spell disaster.

Lastly we have those who track their car or do AutoX. Will attempt to keep this short and sweet. Here is where one may choose to add bigger rotors and better clamping (more pistons) brake system. With rotors, size in not **everything** as you might also be adding unsprung rotational weight (bad). This is why top quality larger rotors usually have LIGHTER WEIGHT aluminum center hubs since it is a 'known good' alternative at saving weight over solid rotors. Am avoiding discussing calculating rotational mass and how it alters the vehicle performance.

As for brake balancing (front/rear biasing) for track, you can either play around with different brake pad compounds and/or have installed a brake bias adjuster. Why have adjustable bias (front/rear balance) of the braking system? Because different tracks and track conditions can be fine-tuned for optimum lap times. As an example, during wet track days you will want to increase the percentage of rear brake biasing a bit.

Brake fade, using the brake system to the point where overheating cause a less effective (or totally vanish) performance can be dealt with through proper cooling. As mentioned earlier, solid is best due to more metal while slotted is second best (with drilled being last). During track events one would measure the heat on the system and choose the right fluid and pads so that their heat rating is within set parameters. If the system is achieving too high a heat, brake cooling ducts can greatly help lower temps to a certain degree. If the brake system is below said parameters, one may choose different pads rated accordingly.

GET REAL:

Frankly, in the end slotted or drilled brake rotors is not needed for the average American driving their car on the street. Speed limit laws in most countries assures you never get anywhere near the edge of stock brake system performance for stopping power or brake fade, wet or dry conditions. It is only those who truly use their systems for AutoX, track days or the like that will want to carefully consider a properly engineer SYSTEM for their given vehicle, driving style, and track conditions.

BLING FACTOR ONLY: Get wherever (sane system) you want to look cool and brag to others, but PLEASE make sure you have the front/rear brake bias correct. Incorrect biasing can KILL you and/or others.

NOTE: there is A LOT of misinformation on the Internet concerning slotted or drilled rotors by inexperiences, uneducated, or skewed marketing people (just as inexperienced/uneducated/marketing people may provide reviews of audio gear). PLEASE talk to TRUE professional engineers who have vast knowledge and experience. BE HONEST WITH HOW YOUR BRAKE SYSTEM WILL BE USED!!! Also, one may choose great rotors and calipers, yet use basic pads/fluids for the street and change pads/fluids for track days.

Please avoid the BLING factor as your brake system is a balance and altering this can cause DEATH! THE LIFE YOU SAVE MAY BE YOUR OWN.

Enjoy the Music,

Steven R. Rochlin

Edits: 70/90/00

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