And more importantly, what should I look for in a replacement rotor? Brand? Material? Other?
BRAKE ROTOR DESIGN
Rotors also differ in the design of their cooling ribs. Vehicle manufacturers currently use over 70 different cooling rib configurations in their rotors. Some ribs are straight, some are curved and some are even segmented. Some ribs are evenly spaced while others are not. Most ribs radiate outward from the center but others zigzag like a maze. Different cooling rib configurations are used to "optimize" brake cooling on specific vehicle applications, and to reduce harmonics that contribute to brake squeal.
Replacement rotors may or may not use the same rib configuration as the original equipment rotors. A rotor supplier may consolidate rib designs to reduce the number of SKUs needed to cover the market, but this may mean compromises in cooling and noise performance on some applications.
Most economy rotors use a "standard" cooling fin configuration, while most "premium" rotors use the same rib configuration as the OEM rotor.
BRAKE ROTOR MATERIALS
Another factor that affects rotor performance is the metallurgy of the rotor itself. The metallurgical properties of the iron determine the rotor's strength, noise, wear and braking characteristics. The casting process must be carefully controlled to produce a high quality rotor. The rate at which the iron cools in the mold is critical and must be closely monitored to achieve the correct tensile strength, hardness and microstructure.
If the casting process is not carefully controlled, the iron may not form the proper microstructure resulting in a noisy rotor or one that lacks proper hardness. A rotor that is too hard may crack while one that is too soft may wear prematurely. Again, economy rotors may not be made to the same level of quality as premium rotors.
COMPOSITE BRAKE ROTORS
Some rotors have a "composite" design instead of being a one-piece casting. A stamped steel center hat is combined with a cast iron ring to reduce the weight of the rotor. Composite rotors are less rigid than solid rotors and must be supported with adapters or large bell caps when they are resurfaced to prevent chattering and flexing.
If a composite rotor has to be replaced, it should usually be replaced with the same type of rotor as the original. Cast rotors are available as a lower cost alternative for many vehicles that were originally equipped with composite rotors, and some technicians believe cast rotors cause fewer problems. But the hat section of a cast rotor is thicker than the original composite rotor and changes wheel offset slightly. This may have an adverse effect on steering geometry (scrub radius) and wheel alignment.
Sunday, March 1st, 2009 AT 4:03 PM