Challenger Brake Rotors: Heavy Metal Discs

The brake rotor is a metal disc that is bolted to the wheel hub and spins with the wheel. The caliper, with the brake pads located inside, slides over the rotor, and bolts to the spindle via a mounting bracket. The brake rotor is held in place by the wheel and the lug nuts.

As you apply pressure to the brake pedal inside the car, the fluid inside the hydraulic lines is pressurized. The pressure is forced through the lines and hoses to the brake caliper. The pressure at the caliper forces the piston in the caliper outward. The piston pushes the brake pads against both sides of the rotor.

When the brake pads are forced against the rotor, friction occurs. This friction transfers the rotational energy of the wheel into heat energy, occurring in the brake pads and rotors.

The brake rotor helps to dissipate the heat away from the brake pads, to prevent ignition and burning of the brake pads. Thus, the brake rotor has two main functions:

• To create friction against the pads, in order to slow and stop the vehicle
• To dissipate heat from braking

Most stock brake rotors are made of cast iron. The pad mating surfaces are machined to a shiny, smooth surface. This prevents unwanted wear and noise. 

There are two basic rotor designs used for automotive purposes: solid rotors and vented rotors. Solid rotors are constructed of one solid metal disc surrounding a center mounting plate, or “hat.”

The brake pads contact either side of the solid disc. These are typically used in rear brake applications, as less braking occurs in the rear, and less heat needs to be removed.

Vented rotors are designed with a solid disc on the inside and outside, where the brake pads contact. Between the two discs, there are solid ridges and hollow vents radiating from the center outward.

This allows air to flow between the two contact surfaces, for better cooling. This style is typically found on the front of a vehicle, where most of the braking is done.

Slotted Rotors: Slotted rotors are rotors that have grooves machined into the braking surfaces. These grooves, or “slots,” radiate from the center outwards, and run in the direction of rotation. The edges of the grooves are chamfered, so as not to catch the edges of the brake pads.

Cross-Drilled Rotors: Cross-Drilled rotors are rotors that have holes drilled through both of the braking surfaces in the same spots. The holes are drilled in a pattern radiating outward from the center, and in the direction of rotation. The edges of the holes are also chamfered, to prevent the brake pads from catching on the holes.

The advantage to having slotted rotors, cross-drilled rotors, or slotted and cross-drilled rotors, is that all of these designs allow for more air contact and flow. This means better cooling and heat dissipation. 

Slotted rotors help to pull brake dust away from the pads. This results in more of the brake pad is in contact with the rotor and more friction. That means better and faster stops. 

Cross-drilled rotors were developed many years ago when asbestos brake pads were common. When asbestos pads were applied to rotors, the heat produced gasses from the pads that became trapped between the pad and rotor. The gases prevented a portion of the brake pad from contacting the rotor. The holes allowed the gases to escape and improve braking.

Today, asbestos brake pads are no longer permitted as a material, so this function doesn’t apply. Cross-drilled rotors today are used for the cooling benefits, as well as appearance, on street cars.

All of these rotors have some disadvantages. Brake pad wear is the primary concern. Because it is similar to running the brake pads over a cheese grater, pads will wear faster than with solid rotors. These rotors also less structurally sound than solid rotors. By drilling and/or slotting the rotor, you are removing material. This compromises stability and the ability to withstand extreme heat. These rotors are much more prone to cracking and failure.

Larger diameter rotors definitely affect the brakes ability to cool. The larger the brake rotor, the more surface area.

The larger the surface area, the more area available for contact with the air. The more area available to contact with the air, the faster heat is available to dissipate away from the brakes. Below is a table listing the diameter of the factory-equipped brake rotors:​​

The first and most important step in preventing damage to your brake rotors, is to break in the brakes properly. After replacing brake parts, take the vehicle for a test drive. Get the car up to driving speed, and gently apply the brakes until you reduce the speed by 10 miles per hour.

Repeat this several times. Then, get the vehicle up to road speed, and gently come to a full stop. Repeat this a few more times, and you should be ready to go.

When driving, be aware of the amount of heat going into the brakes. Do not leave your foot on the brake pedal constantly, or for a long period of time. When descending a hill, use the transmission to help slow the car by shifting to a lower gear. Avoid sudden “slamming on” of the brakes whenever possible.

If you’ve done any modifications to your car to improve horsepower and speed, you should upgrade your brake rotors. This includes an air intake, exhaust, engine tune, etc. With making the vehicle faster, you also need to make it stop faster to counteract all that power.

If you use your vehicle for any type of performance driving, such as track days, racing, etc., it’s also time for an upgrade. The rotors will help to remove brake dust for better friction and allow for better cooling and heat dissipation under high-speed, repeated braking.