|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. In case you are still not quite sure, please read
rotor is so important to a brake system.
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
- Assembly (applicable to two-piece rotors)
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
- 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.