[s-cars] Brake Rotor with Big Reds

[Elijahallen92 at aol.com]

Here is a picture of my Porsche drilled rotors. They have been like this  
since the I took them to the track last year. They are just over a year old.  
There is a crack around just about every hole on the inside rows and now they  
are even showing some cracking on the outer rows. This is enough for me to start 
 looking for solid slotted rotors. Anyone on the list that wants to see this  
picture email me and I'll send it.

Elijah
 
 
In a message dated 5/15/2005 6:46:50 PM Eastern Standard Time,  
keith.maddock at gmail.com writes:

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
negligible).
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!)

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

Also,  RE need for "Big Rear  Brakes"
http://tinyurl.com/26cta


Cheers,
Keith