Most vehicles on the road today are sold with solid, blank rotors installed from the factory. At most, the rotors are vented to allow for better heat dissipation. In high performance vehicles like the E63 AMG, BMW M4, and others, the stock front brakes are either cross drilled, slotted, or both. Often, people will upgrade their stock solid brake rotors to these variants to gain some of the promised brake performance boosts and cool factor that comes with speciality rotors. So, what's the difference between cross drilled and slotted rotors in the first place?
Drilled Rotors
Drilled rotors are based on the solid rotor style and have a pattern of strategically placed holes drilled into the contact surface to achieve improved cooling, gas and dust expulsion, and overall performance. When your brake pads contact the rotor surface, heat is generated and a pocket of hot air is formed between the surfaces as a result. The drilled holes allow this pocket of heated air, dust, and gas to escape through the vents within the rotor and out, resulting in cooler brakes.
The downsides of drilled rotors are few, but they are worth mentioning. In lower quality drilled rotors, typically sold on eBay in "performance brake kits", there have been reports of premature brake failure due to cracking. This is because drilling through the rotors reduces structural integrity versus a stock brake disc that is solid all the way around. Heavy braking, frequent heat cycles, and aggressive driving can all contribute to this point of failure. If you plan on doing any sort of performance driving with drilled rotors, it's important to get quality rotors that can withstand the abuse.
Slotted Rotors
Instead of holes, slotted rotors have vanes machined into their surfaces. The premise behind this feature is similar to drilled rotors as it's intended to help vent brake dust and heated air away from the surface of the rotor to allow for improved cooling. This design also helps significantly improve pad to rotor surface contact over a blank or drilled rotor. Slotted rotors also aid in the expulsion of built up brake dust, significantly more so than a drilled rotor. Additionally, slotted rotors are stronger and less prone to cracking compared to drilled rotors as the structural integrity of the slotted rotors is not compromised during the machining process.
People have pointed out that slotted rotors tend to eat pads faster than solid or drilled rotors. The vanes have sharp edges that bite the pads, which can cause premature wear. This issue can be compounded if you use cheap pads instead of quality pads from Akebono, StopTech, Brembo, etc.
Which One is Right for You?
It's important to consider your driving style and what you'll be using the car for when you decide on upgrading your brakes. For most vehicles, the plain OEM rotors are usually more than enough but for those who see value in upgrading to cross drilled or slotted rotors, weighing the pro's and con's between the two designs in key. If you think you'll be doing a lot of hard braking, perhaps getting slotted rotors is the better option to prevent the cracking that plague drilled rotors. If you prefer the look of drilled rotors and believe they can handle your driving style, go with them and make sure to buy from a quality brand like Brembo or StopTech.
What's your personal opinion on Drilled versus Slotted rotors? Comment down below what kind of rotors you run on your car and tell us about your experiences!
