Repairs that you DON’T need: Drilled & Slotted Brake Rotors

As the destination for Airdrie’s highest quality, longest lasting brake replacements, we’re sometimes asked about installing drilled and slotted brake rotors. As the name suggests, these are brake discs with holes or slots machined into the rotor faces. You’ve likely noticed them on high performance vehicles like Ferraris, Lamborghinis and other exotic cars. And hey, if they’re good for a Ferrari, then they should provide a meaningful upgrade for any vehicle, right? Not quite. Drilled and slotted brake rotors are a bit misunderstood, so we’ve written this article to explain why they’re not a good idea for most daily-driven vehicles.

What are the benefits of a drilled and slotted brake rotor?

How your brakes work is actually pretty simple. Hydraulic force from your brake pedal is transmitted through lines to your brake calipers, which squeeze your brake pads into the rotors. The caliper and pads are stationary, while the rotors turn with the wheels. It is the drag from the pads on the rotors that slows the vehicle.

Drilled and slotted rotors are designed to deal with an issue that occurs during repeated hard braking, such as under racing conditions. When the brake pads are pushed to extreme temperatures, a phenomenon called out-gassing happens; that’s when the pads start to release gases from the binding resins inside the friction material. This creates a boundary layer of air between the pad and rotor surface, reducing friction and therefore reducing the “grab” from the brakes. Adding holes or slots to the rotor gives this out-gassing somewhere to escape, preventing brake fade under extreme hard braking conditions.

Are drilled and slotted rotors beneficial on a daily-driven, regular vehicle?

Ninety-nine percent of the time, they are not. During normal driving, even through the mountains, your brakes should never experience the extreme temperatures where out-gassing occurs. If they do, there are other problems that should be addressed; issues like faulty trailer brakes on towing vehicles, or a car that is grossly overloaded.

A common line of thought here is, “Okay, so they might not help, but drilled and slotted rotors won’t hurt, right?” Unfortunately, hurt they might. Let us explain some of the downsides of drilled and slotted rotors below.

What are some disadvantages of drilled and slotted brake rotors?

Noise Concerns

The interaction between your brakes pads and a drilled/slotted rotor often generates more noise than a solid (or blank) rotor — one reason they aren’t installed from the factory on many vehicles where driver comfort is a priority, even when that vehicle is considered high-performance. This noise is especially noticeable under medium to firm braking. A “whooooooooom” noise when applying the brakes at highway speeds is very noticeable on some vehicles where drilled or slotted rotors have been fitted in a system designed for blank rotors.

Increased Brake Pad Wear

Like a cheese grater (to grossly exaggerate it) the holes and slots in these rotors wear down your brake pads more quickly than a blank rotor does.

Drilled & Slotted Rotors Rust Faster

With all the road salt used in Alberta today, we’re dealing with a new issue in our province: brakes that rust out before they wear out. We’re seeing this most often with electric vehicles, since EVs use their mechanical brakes much less and are already prone to brake rusting issues.

Because brake rotors are made from ferrous metal, they rust when exposed to moisture. This is normal, and most surface rust that develops while your vehicle rests is “wiped” or scuffed off by the pads during your next drive. Sometimes, however, enough rust forms outside the brake pad contact area that it starts to encroach into the rotor face; to the point where the pads can no longer wipe it off. Drilled and slotted rotors provide more “non wiped” areas where rust can (and does) form.

Poor Quality Parts

Have you ever heard of putting lipstick on a pig? This expression refers to making something bad or flawed look better with superficial changes – and that’s exactly what’s going on with many aftermarket drilled and slotted rotors. Sadly, the internet is full of low quality rotors masquerading as an “upgrade” because they are drilled and slotted.

Here’s the deal. It doesn’t matter what a brake rotor looks like; it matters what it is made of. Cheaper brake rotors:

• Have a low carbon content.
• Use cheap materials, with more impurities in the iron.
• Are manufactured with lower-cost casting, less precise cooling control and minimal post-processing.
• Use simple, cheap vane structures between the faces for cooling.
• Are uncoated or use lower quality coatings.

Better brake rotors:

• Have a higher carbon content, to absorb and spread heat more evenly.
• Use better quality cast iron with a more uniform grain structure, often alloyed with elements like molybdenum or chromium.
• Are manufactured with more precise machining, controlled cooling (which reduces internal stresses) and superior balancing/processing.
• Use advanced vane structures (curved, pillar, directional) that match your factory rotors.
• Use higher quality coatings that resist rust and last longer.

High quality rotors perform better, last longer, are less prone to thickness variation (causing vibration) and rust less. You will be far better off with a good quality blank rotor than a lower quality drilled/slotted part. Even if everything else was exactly the same, a blank rotor will perform better in most cases because drilling reduces the mass, strength and surface area.

What about vehicles that repeatedly “warp” brake rotors?

Have you ever experienced a shaking steering wheel or a pulsing pedal while braking? When it’s not caused by rust, this is usually the result of “warped” brake rotors. The correct term for this is thickness variation; distortion of the rotors due to heat. This distortion happens when the brakes are overheated due to aggressive driving or vehicle mechanical issues. With their superior metallurgy, premium rotors will resist this distortion better while cheaper rotors are more likely to “warp”.

You might believe that drilled and slotted rotors would offer a solution here, but in many cases, the opposite is true. As mentioned above, drilled and slotted rotors have lower mass and surface area; there’s just less metal available to absorb the heat. When this lower mass is paired with a cheap vane design, lower carbon content or other cost-cutting efforts found in many inexpensive drilled and slotted rotors, it’s a recipe for repeat rotor failure.

Airdrie’s highest quality, longest lasting brake replacement:

Looking for a quality brake replacement, for a fair price, and backed with the longest workmanship warranty in Alberta? You’ve come to the right place. Our caring, non-commission Technicians take pride in pairing premium ceramic pads with high carbon, coated brake rotors and doing all of the little things right. We will meticulously clean your wheel hubs, use the most expensive brake lubricant available and even sandblast & refinish your brake calipers on our way to delivering a repair that we can both be proud of. You will receive our 3 year/100,000 kilometer guarantee against defects or issues.

To obtain an estimate, please contact us to schedule a brake inspection.