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Old 06-03-2014, 05:35 PM   #1
KaBoom1701
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Exclamation THE ARGUMENT AGAINST CROSS-DRILLED VENTED ROTORS

THE ARGUMENT AGAINST CROSS-DRILLED VENTED ROTORS

(by
Marcus Blair Fitzhugh, © 2007, reformatted for clarity)

They're for looks. OK, maybe removing material is good for reducing un-sprung weight, but that's
about it.
It doesn't do anything for heat dissipation. The front discs on my car are vented. They're vented
on every car that I know of. When a vented disc is spinning, it pulls air from the center of the disc,
through the channels (which are called vanes), and out the rim of the rotor. The vanes in a
Mercedes-Benz rotor are also curved. That's because the engineers who design rotors know that
curved vanes move cooling air more efficiently than straight vanes, which are less expensive to
manufacture. This cooling air moves in a radial direction. We can view the spinning rotor as an
efficiently designed air pump.
The cross drilled holes in the disc must aid in this cooling design, right?
Not quite. Let's think about what happens. Air flow follows the path of least resistance. Does
the air that's flowing from the center of the rotor to the path of least resistance go to the wide
open vanes, or make a 90° turn, to holes that are drilled axially in the rotor?
So, since the holes aren't there to pull air in, and they don't aid in pushing the air out, you
may be wondering why they were invented.
Cross drilled rotors were originally designed to cure a problem called
out-gassing. Outgassing

was a problem where pads would overheat, and the binding material (glue) would
melt down and vaporize. This vapor became trapped between the pad and the rotor, making
the pad to float on a layer of vapor. The purpose of cross-drilled rotors
was to allow the gas to

escape.
The key word there is “was”. Better high performance pad design has eliminated this problem.
If you simply can't bring yourself to believe that cross-drilled rotors are all hype, consider this.
Why aren't cross-drilled rotors used in
NASCAR, Formula 1, Automobile Club de l'Ouest (ACO),

or
ALMS? If drilling holes in rotors was the hot ticket, at least one team in one of those

associations would use them.
Some people will claim, "
Motorcycles use them!" This is true, however, if you look carefully at a

motorcycle disc you will notice they aren't vented, motorcycles use solid discs. They can use solid
discs because they carry one eighth the weight of a car. If you drive a 400 pound car, solid,
cross-drilled discs may be an option.
Still have doubts?
Here are some quotes from brake engineers, brake manufacturers, and automotive
publications in regard to cross-drilled, slotted, and plain rotors.
AP Racing
:

"
Grooves improve 'cleaning' of the pad surfaces and result in a more consistent brake

performance.
Grooved discs have a longer life than cross-drilled discs.
"

Baer
:

"
What are the benefits to Cross-drilling, Slotting, and Zinc-Washing my rotors?

“In years past, cross-drilling and/or Slotting the rotor for racing purposes was beneficial by
providing a way to expel the gasses created when the bonding agents employed to
manufacture the pads. However, with today’s race pad technology, out-gassing is no longer
much of a concern.
Slotted surfaces are what Baer recommends for track only use.

Slotted only rotors are offered as an option for any of Baer's offerings.
"

Darrick Dong; Director of Motorsports at Performance Friction
:

"
Anyone that tells you that drilling makes the disc run cooler is smoking crack."

Waren Gilliand
:

(Mr. Gilliland is a well-known brake engineer in the racing industry and has more than 32 years experience in
custom designing brake systems ...he became the main source for improving the brake systems on a variety of
different race vehicles from midgets to NASCAR Winston Cup cars.)
"
If you cross drill one of these vented rotors, you are creating a stress riser that will

encourage the rotor to crack right through the hole. Many of the rotors available in the
aftermarket are nothing more than inexpensive offshore manufactured stock replacement
rotors, cross drilled to appeal to the performance market.
They are not performance rotors

and will have a corresponding high failure rate
"

Grassroots Motorsports
:

"
Cross-drilling your rotors might look neat, but what is it really doing for you? Well, unless

your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled
because early brake pad materials gave off gasses when heated to racing temperatures, a
process known as gassing out. It was an effective solution, but today's friction materials do
not exhibit the some gassing out phenomenon as the early pads.
Contrary to popular belief, they don't lower temperatures, (in fact, by removing weight

from the rotor, they can actually cause temperatures to increase a little.)
“These holes create stress risers that allow the rotor to crack sooner, and make a mess of
brake pads--sort of like a cheese grater rubbing against them at every stop. Want more
evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the
hot ticket, these teams would be doing it. “
“Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows
for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the
brake pads over time, helping to reduce the glazing often found during high-speed use which
can lower the coefficient of friction.
“While there may still be a small concern over creating stress risers in the face of the rotor, if
the slots are shallow and cut properly, the trade-off appears to be worth the risk, (have you
looked at a NASCAR rotor lately?)

Power Slot
:

"
At one time the conventional wisdom in racing circles was to cross-drill brake rotors to aid

cooling and eliminate the gas emitted by brake pads. However, today's elite teams in open
wheel, Indy and Trans Am racing are moving away from
crack prone, cross-drilled brake

rotors
in favor of rotors modified with a fatigue resistant slotting process.
"

Stop Tech
:

"
StopTech provides rotors slotted, drilled or plain. For most performance applications slotted

is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as
well as increasing the "bite" characteristics of the pad.
“A drilled rotor provides the same type of benefit, but
is more susceptible to cracking

under severe usage
. Many customers prefer the look of a drilled rotor and for street and

occasional light duty track use they will work fine.
For more severe applications, we recommend slotted rotors."

(Note that even though Stop Tech sells both drilled and slotted rotors they do not recommend
drilled rotors for severe applications.)
Wilwood
:

Q: “
Why are some rotors drilled or slotted?

A: “
Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching

for ways to minimize un-sprung weight.
Drilling diminishes a rotor's durability and

cooling capacity
"

© 2007 Marcus Blair Fitzhugh
Signal to Noise
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Old 06-04-2014, 09:02 AM   #2
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My SRT8 300 came with Brembos and slotted from factory...along with a raceday package. My SS will get slotted upon 1st needed replacement.
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Old 06-04-2014, 09:31 AM   #3
Dexman1349
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What about slotted rotors?
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Old 06-04-2014, 11:27 AM   #4
Dropspeed
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AMEN......but sheeple will continue to spend money on parts that are not needed.
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Old 06-04-2014, 11:09 PM   #5
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^^ Too True and telling them any different is like telling them the Easter Bunny died at the hands of Chim Chim.

T.
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The drag strip is like sniffing glue, it's cheap, it's a decent buzz, it doesn't last long and they are all the same.
Road racing is like China White Heroin, the buzz is stronger, the high lasts for hours, it's extremely addictive and they are all different.
I can't wait for my next
Track fix.
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