by Dave Zeckhausen
Which rotors should you choose for your vehicle?
|Slotted & Drilled||2-Piece Floating|
Smooth rotors offer the quietest operation, lowest dust and longest pad life. If you have a luxury car not driven aggressively, this may be your best choice. Often used by endurance racers who need their brakes to survive an extended race without a pad change and are willing to give up some performance to achieve that. Usually these are the lowest cost option.
Some premium rotors are available with directional internal cooling vanes (there's a left and a right part number), even though the factory rotors may use straight vanes. These offer enhanced cooling over the stock rotors. See "Which Way? How to properly install plain, slotted or drilled brake rotors" for more details.
Slotted rotors improve stop-to-stop consistency by preventing reduction in friction from pad outgassing and lubricating brake pad particles (also called "incandescents") which are otherwise trapped between pads and rotors. Pad long-term performance is also made more consistent, as slots shave away glaze formation caused by pad overheating, slowly exposing fresh pad material each time the brakes are applied. The tradeoff is slightly reduced pad life. Although modern pad compounds make this less important, slots offer improved bite and slightly higher friction level than smooth rotors.
Where allowed by rules, slotted rotors are by far the top choice for competition vehicles. These are the best choice for heavy trucks and SUVs, particularly when extra bite is desired for towing, especially when aggressive pads are not available.
Disadvantages include slightly reduced pad and rotor life, some low frequency rumble and pedal flutter when braking hard from high speeds. If the slots are improperly machined, all the way to the outside edges, then rotors may develop cracks sooner than plain or properly slotted rotors.
Drilled rotors offer slightly more bite and friction than slotted rotors. As with slotted, pad coefficient of friction remains more consistent over their lifetime. Wet bite is better than plain or slotted rotors, so these may be the best choice for areas with frequent, heavy rainfall, like Seattle or Singapore. Weight is reduced by about 0.2 pounds per rotor, depending on size and drill pattern.
Disadvantages include possible uneven rotor wear, typically concentric groove formation, although this is mostly an aesthetic concern. A major disadvantage is accelerated formation and spreading of cracks under racing conditions. For this reason, drilled rotors should be avoided for track cars, unless required by the rules. A common myth is that they have lower performance than smooth rotors, due to reduced surface area and are for looks only. This is completely false and, in fact, the opposite is true.
Slotted & Drilled rotors offer a compromise, midway between the benefits of slotted rotors and drilled rotors. These are fine for street applications, but should be avoided for track cars. Slotted & drilled rotors are starting to appear as OEM parts on some high-end cars, including BMW and Mercedes. This is being pushed by marketing and not by engineering. It is a common misconception that drilled and slotted rotors have higher performance than drilled rotors.
2-Piece Floating rotors consist of replaceable iron "friction rings" assembled with float hardware to aluminum hats or mounting bells. 2-Piece rotors can offer substantial weight savings of as much as 10 pounds per rotor, depending on the application. The design allows the friction ring to expand as it heats, without being trapped by the center section. Under racing conditions, this prevents rotor "coning" and subsequent tapered pad wear and spongy pedal, and reduces rotor cracking. Conductive heat transfer to the wheel bearings is reduced, potentially improving bearing longevity. For track cars, floating rotors are the best choice and should be used when available.
Outer friction rings may be replaced when worn, while reusing the center hat. Click HERE for details.
Disadvantages include significantly higher initial cost. For street cars driven in winter climates with high-salt/chemical use, corrosion between the iron friction rings, aluminum hats, and float hardware may lead to reduced product lifetime. This can be mitigated by occasionally flushing the brakes with water or swapping back and forth between "summer" and "winter" brakes.
The rotors described above are the same external dimensions as the factory rotors. Zeckhausen Racing carries a wide range of rotors from Centric Parts, StopTech, DBA and Girodisc. Brake upgrades with larger rotors and fixed, multi-piston calipers are also available.