Why The Rotor Is So Important


Energy Conversion:

When a brake is applied, all of the kinetic (motion) energy of the vehicle is converted into thermal energy.

Energy (Heat) Factors:

E = 1/2 MV²


    E = Kinetic energy generated
    M = Vehicle weight
    V = Speed of the vehicle

Therefore, the brake power required to stop the vehicle is directly proportional to the vehicle weight. Thus if the weight of the vehicle is doubled, the energy of motion (converting to heat) is doubled. The effect of vehicle speed is even more serious. If the speed of the vehicle is doubled, the brake system would require four times the power to stop the vehicle, which means the brake mechanism must absorb and dissipate four times as much as heat.

The total energy resulting from the increase of vehicle weight and speed is multiplied, i.e. if both the weight and speed of a vehicle is doubled then your brake system would require to generate eight times more power or eight times more of heat to absorb and dissipate.

Brake Temperature:

The amount of heat generated by brake applications usually is more than the rate that a brake mechanism can absorb and dissipate. This will result in brake temperature increase. In normal brake applications, the time interval between brake applications (brake cycles) allow the heat to cool off. However if repeated abrupt or panic stops are made within very short time intervals, the brake temperature will continue to rise. This will result in brake fade or brake failure and damage to the brake system including brake pads, brake rotors or drums, calipers, and brake fluid.

Rotor - The Heat Sink:

Since all the converted heat needs to be absorbed and dissipated,the rotor comes into play as the “heat sink,” – similar to a water sink. As the rotor heats up, it absorbs heat just like a water sink holds water from a faucet. If the water pours into the sink at a rate faster than drain can handle, the water will overflow. Likewise, if the temperature of the rotor increases at a rate faster than the rotor can cool down, consequent damages are likely to occur. In one case, you end up with a wet floor, and in the other, a damaged brake system. In some extreme cases with too much heat, the tires could be set on fire.

Now we know how important a brake rotor is to a brake system. We need a bigger heat “sink” and efficient heat "draining" system to prevent heat from overflowing.

Rotor Factors:

Increasing the holding (thermal) capacity means enlarging “sink” size, but in brake rotor instance this may be impractical, as it would also increase the rotating mass, which slows down the acceleration and as deceleration. This is not a desirable solution. So the challenge is to produce a rotor with the same mass, yet can manage or hold the same amount of heat longer, without overflow. To achieve this goal there are two main issues to overcome:
   1. A better material that is more resistant to higher temperature with good thermal stability
   2. Improved designs that can dissipate the heat faster

Rotor Material:

Rotors are usually made of gray iron due to its superior heat handling and damping (vibration absorption) character. SAE specified J431 G3000 for the automotive brake rotor and drum which has a Brinell hardness of 187-241, and a minimum tensile strength of 30,000 psi with pearlitic microstructure. A casting that meets both physical property and chemical composition requirements can still fail prematurely in brake applications due to inferior microstructure. Microstructure is the most important criteria in dictating the rotor performance under extreme heat. Microstructure is the matrix of the cast iron which is visible only under microscope (100X). The subtle difference between the “water” and “heat” sink (rotor) is that the water sink capacity is straight on volume but the rotor heat handling capacity also related greatly to microstructure. Microstructure analysis involves examining the graphite distribution and matrix structure of the cast iron.

A standard rotor cast iron should have the following graphite formation: (per ASTM A-247 classification)

Type of graphite: Type of flake:

Type VII, in the flake graphite form

Type A

Distribution: Preferably randomly distributed

Flake size:

Size 3

Size 4

This matrix should be predominantly pearlite, with not more than 5% ferrite and less than 1% cementite.  With very few exceptions, OEM (Original Equipment Manufacturer) rotors that come with the car or replacement rotors from car dealers usually meet these standards. There are companies that make aftermarket replacement rotors. Replacement rotors are also referred to as stock rotors, because they have the same dimensions as OE rotors and do not have any drilling or slotting modification. Unfortunately, the quality from these aftermarket suppliers is rather inconsistent. Almost every manufacturer claims to meet or exceed OE specs, but in reality, very few actually live up to their claims. Their rotors are usually inferior to OE rotors. Even in the performance market, if you can find a rotor that is made to OE standards, consider yourself lucky.

As we know, these so-called manufacturers usually just fabricate (drill and/or slot) from aftermarket “stock” rotors to make their rotors have the “performance” look. The majority of consumers buy these “performance” rotors because of their look and the way they were marketed, without knowing that these "upgraded" products perform, in most cases, worse than their OE rotors.

RacingBrake is the company that supplies the true performance rotors for different level of braking demands - from street performance HP rotors to track racing competition two-piece rotors and extreme performance club race rotors. We have added different alloys to gray iron to improve its strength and wear resistance. For higher carbon contents, our rotors are highly resistant to thermal fatigue, a major cause of warping and cracking. We also heat treat our rotors for more stabilized performance in racing applications. Our rotor matrix is pre-dominated with fine laminate of pearlite which provides a consistent hardness of Brinell 200-210 on the braking surface. This enables the rotor to handle more aggressive brake pads without wearing out prematurely.

Rotor Design:

As we mentioned earlier, a better-designed rotor can help to dissipate heat faster (more efficient) and therefore runs cooler, reduces the chance of heat buildup. RacingBrake makes rotors based on application need, rather than simply duplicating OE rotors, like most aftermarket suppliers do. See our list of applications where we have taken the OE straight vane design and upgraded it to our curved vane design. (Click here for full list). Creating curved vane rotors requires separate mechanical tooling for the left and the right sides. Due to this, the manufacturing costs are higher, but this design greatly improves air circulation. Some competitors claim “pillar” or “kangaroo paw” vane designs which are essentially non-directional as straight vane designs, and their claims of improved of cooling effects have yet to be proven.

The convergent vane is RacingBrake’s patented design (Click for photo). The air inlet is wider - admitting more incoming cold air, but the discharge side is narrower - expelling the hot air out more rapidly. This results in a more efficient heat exchange, and therefore, cooler rotors.

Our patented center mount two-piece rotor design is another invention that breaks the tradition of two-piece rotor design. Other companies produce a surface mounted two piece rotor, trying very hard to increase the gap between the hat and disc surface for admitting outboard air. Our innovative center mount design has wide and heat balanced open air inlets on both the inboard and outboard sides. This creates optimal air circulation that guarantees our discs to be 50-80 degrees F cooler than conventional surface mounted rotors. Click here for feature comparison and benefit description.


The above just highlights some of the fundamental facts of why a rotor is so important to the brake system, and that better materials and rotor designs can greatly enhance overall brake performance and make driving or racing safer. Unfortunately, many people spend their money in turbo charging their car for faster acceleration (i.e. time from 0 to 60 mph), but often fail to pay the same attention in getting their brake systems compatibly upgraded.  We believe this is partially because there are not many choices out there, but also because the market is loaded with gimmicks and confusing or misleading information. RacingBrake intends to fill this void with true performance quality brake systems that any automotive enthusiast deserves.