What rotor is good for me?
Based on our 20-year experience in the brake business, we would like to present a very specific guideline to consumers for what to look for and what kinds of questions to ask when it comes to purchasing brake rotors.
Most people are aware that the brake system is the most important element to a car, and out of this system the brake rotor is the most essential piece.
We will purposely be isolating other components such as calipers, pads, brake hydraulic fluids etc. from this discussion so that the brake rotor can be independently evaluated.
There are four major criteria that dictate the performance of a brake rotor:
- Material
- Design
- Machining
- Assembly (applicable to two-piece rotors)
Material: Different casting materials or alloys can be specifically formulated for different types of driving applications i.e. street, track, or racing. It is important to be aware of the availability from your supplier before purchasing a rotor. Heat treatment to the rotor casting adds the benefit of relieving stress and improving the thermal stability of the rotor. So when inquiring about a high performance rotor, you should find out:
- Is the material right for my application?
- Has any alloy been added to the iron?
- Has the casting been heat-treated?
- What is the matrix and microstructure of the casting?
- Is there any traceability such as Manufacturer, P/N, lot number, and production date code on the rotor?
- Is the hat made from billet or forged aluminum (two-piece rotor)? Forged aluminum provides better strength and rigidity.
Design: A better-designed rotor can handle more heat with the same weight. Why? Efficient air circulation keeps the disc cooler. There are different ways to achieve this result including a commonly known design such as curved (directional) vanes. There are also some patented designs such as Stoptech's™ "Aerorotor," DBA's "Kangaroo Paw," Brake Pros' "Pillar Vane," and RacingBrake's™ "Convergent vane Center-mount." Another area to look at on one-piece rotors is how a design can add the strength to prevent the disc from warping, especially for rotors with small hats and large disc diameters (such as Subaru WRX)
Machining: Precision machining is a critical process to assure the rotors are within the tolerance for flatness, thickness variation, parallelism, and run-out. The disc surface should have non-directional cross-cut grinding finish for easy bed-in. Each manufacturer might have its own standard, but published or claimed data may not necessary represent the actual products. We recommend that consumers rely on a reputable and well-established manufacturer. Try to avoid sources such as eBay or unidentified offshore sourcing in the web forums’ group buys. Find out from the group buy administrator about the rotor source before committing to purchase.
Assembly (two-piece rotors): The connection between the rotor and hat, as well as the hardware used to connect the two, can vastly affect the performance of a brake rotor. However, this is seldom addressed in the industry.
- Is the rotor true floating and how (e.g. the rotor mounting holes must be oblong)?
- What kind of hardware (size and grade) is used - The simpler and fewer parts, the better. The rotor must hold constant torque during extended period of racing/driving regardless of heat and driving conditions.
- Will the hardware cause any rattling noises?
- Avoid assemblies that simply have round holes on the hat and rotor and are fastened with regular nuts and bolts. These types of assemblies have no floating feature and deceive the consumer because they look like two-piece rotors and emphasize their lighter weight due to the aluminum hat.
- Unless you are buying a two-piece rotor from a reliable source, you may just be paying a higher price for the look and weight saving. Performance, in many cases, may be worse than a low cost one-piece stock rotor.