[s-cars] Brake Rotor with Big Reds

Keith Maddock keith.maddock at gmail.com
Sun May 15 18:46:37 EDT 2005

James Murray (QA/EMC) <james.murray at ericsson.com> wrote:
> Interesting, I recently read the following on KVRperformance web site: 

A good reminder that just because it's on the web, doesn't mean its true :-D
Comments below directed at website, not at Jamu !!!

> Cross Drilled Rotors: 
> Cross Drilled Discs offer an enhanced initial bite (more responsive,
> especially in wet weather) 

Agreed, compared to OEM or "plain" rotors. 
However, slotted rotors have the same advantage here.

> and greater heat dissipation (reduction in heat induced fade - "brake
> fade")as compared to O.E.M. 

This is a very dubious but common claim.  Many individuals experienced
with braking systems or racing cars can even claim the opposite.

Brake temperature is a function of three things:  Heat In (stopping
energy), Heat out (cooling) and thermal mass of the brake rotor.

If you remove 10% of the mass of the rotor, then the brakes will get
10% hotter.  So already the you must have improved cooling by 10% by
drilling the holes.  Then to actually see a reduction in temperature,
you must have improved cooling by OVER 10% by drilling holes.

> They may also last longer than O.E.M. rotors (depending on your braking
> style), 

"may" being the key word here.  I give this a 1% chance.

> with 40% Better Cooling, 

BS!  I don't think there is much data available to back up such a claim.

> 20% better stopping

No brake rotor can really offer " better stopping" ALL THE TIME unless
the original brakes aren't strong enough to drive the wheels into slip
to activate ABS!  They CAN reduce lost stopping ability by delaying
the onset of brake fade...

> improved wet braking, 

As above, the slotted rotors have the same advantage here...

> reduces rotor warpage, 

I don't know anythign to dispute this, but i find it dubious.  Any
time you remove material from an original object you reduce its
strength.  So by reducing the strength, that would naturally make it
more prone to rotor warpage. This claim is hinged on the dubious claim
that drilled rotors have better cooling, see above.

> less brake fade and longer life. 

See above....

> Gas Slotted Rotors: 
> Slotted discs offer cleaning of the friction material (brake pads), but do
> little in terms of additional heat dissipation. 

Agreed here - the key benefit being able to get the water out of the
way in wet braking situations, as well as "pad gas" - though with most
modern compounds, such outgassing is a thing of the past....

> Slotted brake discs do not cool better than cross drilled discs

Dubious, see above !

> or even standard discs. 

This is one of the few statements I actually agree with...

> The face grooves will slice the brake pad material allowing the pad to bite
> harder into the disc, therefore causing an increase in disc temperatures. 

This is a huge stretch:
If the pad "bites harder", then  you might stop faster.  IN any case,
the total energy put into the brake disc is the same, therefore the
disc temperature will be the same. (since we already agreed that
cooling isn't improved, and the difference in thermal mass is
In a very short time perspective, the disk temperature MAY be
marginally faster since if you stopped faster, the discs had less
cooling time during the stop.    But really, most drivers will
modulate the brake pressure to get the stopping they want, if the pads
really are "biting harder and stopping the car faster" then the driver
will let off a little bit anyway....

> Important Note: Proper slotting of a brake disc does not run off the outer
> diameter of the brake surface. 
> This method can promote cracking as all brake discs expand with their
> release of thermal energy. 

Agreed here - and then again they expose the biggest disadvantage of
slotted rotors - every single hole drilled promotes cracking !

The one time I tried to fit drilled brake rotors to my 968CS resulted
in them cracking within 17 laps at the Nordschleife (a mere 240 track
miles).  This compares quite poorly to several sets of OEM "plain"
rotors which lasted 150+ laps (2100+ track miles).

THAT SAID:  If you have nice big brakes and you're not getting them
hot alot (racetrack), then you'll probably not have a problem with
drilled rotors as you wont be going through the thermal cycling that
causes them crack.  And they do LOOK cool at least :-D

On a related subject, I've found the following article to be quite
insightfull and accurate (personal experience correlates well to what
he writes!)


Also, RE need for "Big Rear Brakes"


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