Rick's Free Auto Repair Advice

Should I buy slotted drilled rotors?

What are the advantages of slotted drilled rotors?

Did you ever wonder if slotted drilled rotors would provide better braking on your family car or truck? Here’s some info right from the experts.

Brake rotor temperatures

When you apply the brakes, the pad’s friction material and rotor convert the vehicle’s motion into heat—a lot of heat. You can calculate exactly how much heat if you know the vehicle weight, swept area of the rotor (the part the pad clamps against), the rotor’s mass, and vehicle speed. If you don’t want to do the math, trust me, it’s hot. In fact, a Formula 1 race car can generate 1,000°F. Most car fanatics figure that since racing cars use slotted drilled rotors and those rotors can handle 1,000°, they must be great for their family cars and trucks. Ah, not so fast. Let’s take a look at the complete picture.

Brake pad fade

When you stomp on the brakes and they heat up, they can reach a critical point called “fade.” At the fade point, the brake pad resins (the material that hold the friction portion together) begin to vaporize, causing a gas layer between the slotted brake rotorpad and the rotor’s swept area. Think of this like brake pad hydroplaning. I know where you’re going with this; you assume that drilled and slotted rotors relieve the gassing pressure and reduce the hydroplaning effect of fade, right? Well, you’d be a bit off base because modern brake pads are far less prone to this phenomenon than older brake pad formulas.

Braking heat

That doesn’t mean new brake pads don’t generate heat, they do. slotted drilled brake rotorBut the question is, does stopping with ordinary brake pads and rotors generate enough heat to cause fade? Keep in mind that brake heat dissipates two ways; the majority of the heat is removed due to the pumping/cooling action of the rotor vanes, and the rest through the caliper and brake fluid. When brakes heat up to near the fade point, enough heat has already entered the brake fluid, causing it to boil.

Do slotted drilled rotors aid in cooling?

That’s the $64K question and the answer is no. The biggest advantage of slotted drilled rotors is that the holes and slots literally scrape off the face of the brake pads, “refreshing” them with each rotation. They provide a minimal cooling advantage, if at all. Depending on how the slots are designed, that refreshing feature may actually cause the pads to wear out faster.

If you want better braking, get better cooling

Rotor vane design is the single most important feature to look for in a brake rotor because the pumping action is far more effective than the slots and holes. Remember, the vanes are a centrifugal fan that suck air into the rotor near the hub and throw it out the vanes on the rotor’s circumference. Car makers spend a lot of money and engineering time designing these “fans” and that’s what makes OEM rotors more expensive. Factory rotors generally have more mass than economy aftermarket rotors as well. More mass, bigger fans, more vanes all add up to better cooling.

The downside to slotted drilled rotors

High quality drilled rotors generally don’t crack. But economy drilled rotors do. If you’re going to add them, make sure you buy premium rotors. And be prepared to change your brakes more often since they tend to wear out pads faster.

Posted on by Rick Muscoplat

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