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.
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.
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
Outer friction rings may be replaced
when worn, while reusing the center hat.
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.