Different Types of Brake Rotors

Brake rotors (aka brake discs) are an essential part of your vehicle’s brake system and are the friction surface that the brake pads squeeze to slow down the wheel’s rotation. Compared to a bicycle; a bicycle rim serves the same function as a brake rotor/disc. When the bicycle brake pads squeeze the rim, it slows you down. Similarly, on a vehicle the brake pads clamp onto on the rotor/disc when you hit the brake, and they need to be working properly if you want your vehicle to stop.

When your brake rotors overheat, your stopping distance will increase and brake pads can deteriorate. This can lead to severe problems in how your vehicle handles braking and stops and increase safety risk to yourself and others on the road. Here’s a breakdown of the different types of brake rotors so you can determine which is best for your vehicle. Schedule an appointment with us for brake rotor service and questions.

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Cast iron rotors

Cast iron rotors are the most common type of brake rotors available. They’re available as either one or two-piece parts and can work in most types of vehicles. (High performing vehicles will need a two-piece cast iron rotor.) Though they’re the most common, cast iron rotors are also the heaviest option. This can impact your vehicle’s handling since it affects how much your car weighs, especially by your front wheels.

High carbon rotors

These rotors are actually made from iron; they just have carbon mixed in. The metallic content of high carbon motors keeps the rotor from cracking and also reduces vibrations and noise. These rotors are also able to withstand and dissipate a lot of heat quickly. The catch is that high carbon rotors are more expensive than standard cast iron rotors.

Steel rotors

Racers traditionally love using steel rotors because they’re significantly lighter and thinner than cast iron rotors. They also handle heat better. The main downside is that they aren’t as durable as other types. Warped steel rotors can cause a loud noise and even a pulsating pedal every time you brake.

Layered steel rotors

A way to get around the warping that some steel rotors experience is by layering sheets of steel together and then laminating them. Layered steel rotors are preferred choice over standard steel rotors for racers. Primarily you’ll see these on professional racing vehicles, since most manufacturers aren’t putting them into passenger vehicles.

Aluminum rotors

Aluminum is another lightweight material, but aluminum rotors tend to melt at a lower temperature than some of the other rotor materials out there. You’ll find them on motorcycles rather than cars, trucks, and SUVs. Since motorcycles weigh less, braking is easier on the rotors and doesn’t create as much heat.

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Ceramic rotors

Most high-end luxury cars have ceramic rotors (think Ferrari or Porsche). Ceramic rotors have the highest heat capacity out of all the rotor types. They’re able to maintain a consistent force and pressure as the rotor temperature rises, giving drivers a smooth ride no matter the elements. These rotors are significantly lighter than iron and steel rotors. In short, ceramic rotors offer light weight high performance braking. They are expensive which is why you’ll usually only find them in high performance cars.

How to choose the right rotor for your vehicle

Does a rotor need to be machined?

No.

What causes a rotor to crack?

Brake Rotors do not crack from hitting a pothole or curb; they break due to the stress of heat and cycling from hot to cold. Also, mechanical stresses from stopping the vehicle can play a part. Every time the brakes are applied, the rotor heats and expands. After the calipers release, the rotor cools and contracts. This can create fatigue in a rotor that can cause cracking and structural failures. A replacement rotor that has been engineered and manufactured has built-in features to manage the heat cycles’ stress. It first starts with the design of the fins and hat structure. The most critical area of the rotor is where the rotor’s plates connect to the hat. Some rotors will have special heat dams to control the different expansion rates of the rotor and heat. Next, how the rotor is manufactured can prevent cracks. The casting process’s heat and energy and how the rotor is cooled before it is machined can cause or reduce stress in the rotor.

Are there any safety certifications or requirements for replacement rotors?

No. A replacement brake rotor or pad does not have to be tested to any specification by the government in the U.S. For new vehicles, the DOT tests the brakes as an assembled vehicle under specific conditions. The car must stop below a specified distance under different loads, scenarios, and pedal pressures. Brake rotor manufacturers must engineer their rotors to operate simultaneously or better as the OEM rotor. Deviating from the OE design to save money can result in a compromised brake system. The Society of Automotive Engineers (SAE) has developed a series of tests on a brake dynamometer to test replacement brake rotors for cracking resistance. The SAE test subjects a rotor to 150 heat cycles. A heat cycle is when a rotor is cold and brought to a high temperature. During a heat cycle, a rotor will expand and contract. This can create fatigue in a rotor that can cause cracking and structural failure. The tests’ objective is to thermally and mechanically stress the rotor so any metallurgy or structure deficiencies are exposed.

Can corrosion compromise the structure or the rotor?

Yes. Excessive corrosion in certain areas of the brake rotor can contribute to structural failures. Also, excessive wearing of the brake rotor working surface beyond the discard specification raises the probability of rotor failure.

Do special finishes on the rotor help its performance?

No. The dull silver finish on most premium brake rotors is known as a Goemet coating. Once the brake pads make contact with the rotor, the layer will be removed. These types of rotors are ready to install straight out of the box. The brake rotor needs to be free from grease contamination. The coating is designed not to contaminate the brake pad material and help in bedding the new pads. Geomet coatings are applied to all the surfaces of the rotor, including the fins and hat.

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