[Supras] stock brake rotors

[Jeff Mohler]

Oh yes, but surface area for cooling WRT drilling, hardly any at all,
because the holes are not receiving that high volume air at a high
pressure the same way that the surface area IN the rotor core does.

Ppl think surface area as a radiator, and that doesnt help anything.


Drilling also reduces important mass that you need to control temps with.


Thickness does aid braking power, because all things being equal, a
thicker rotor runs cooler and allows a LONGER usable pad application.



On Fri, Apr 11, 2008 at 12:04 PM, Walker, Brian (Rich. Dist)
<Brian.Walker2 at vdot.virginia.gov> wrote:
> But I was a thermo major :)
>  Heat transfer is derived from surface area and temp. differential. Since
>  you've got huge differences in temp during braking (rotor vs. pad face),
>  there's a lot of heat transferred to the rotor through the outside
>  surface. Since's there's a much smaller temp difference for cooling
>  (rotor temp vs. air) you need more surface area to cool (accomplished by
>  lots of air across the vented center)
>  You're still talking surface area, just not the area that's seen on the
>  outside of the rotor. A reason BBK's have thick rotors, more surface
>  area for cooling, thickness of the rotor does nothing for braking power.
>
>  Just wanted to point out that surface area does matter, a lot.
>  Brian
>
>
>
>  -----Original Message-----
>  From: Jeff Mohler [mailto:speedtoys.racing at gmail.com]
>
>
> Sent: Friday, April 11, 2008 1:31 PM
>  To: Walker, Brian (Rich. Dist)
>  Cc: Khalid Almufti; Supras at supras.com
>  Subject: Re: [Supras] stock brake rotors
>
>  Everyone is told that..but..it just isnt true.
>
>  Theyre machined..it makes no difference how the hole got there, the
>  outside edge of the hole is where it will split under enough expansion
>  stress.
>
>
>  Now..why are they there??
>
>  1:  Looks sporty.
>  2:  IF theyre there on a true race car, theyre dropping mass that way,
>  but the braking system is already designed to run cool enough to NOT
>  FAIL the rotor by cracking.
>
>  I you look at how airflow moves through a rotor, it becomes instantly
>  clear why holes dont help.
>
>  If you consider that it takes 3 seconds to get a rotor to 1500d in
>  braking, and maybe a mile to get it down to where it was
>  before..."surface area" doesnt aid in cooling on a track whatsoever.
>  Its that large volume of airflow moving thru the rotor core.  Holes
>  reduce the pressure differential at the hub where air enters the rotor
>  core, and drops the CFM that it flows.
>
>  GO find a thermodynamics major and talk about drilling holes in a
>  rotor...not supraforums.com or some vendor that wants to -sell- you
>  this process.   I will be the first to talk you out of it on a track
>  car if you bought rotors from me.
>
>  GO to a club racing event like SCCA or NASA, find 3 cars out of 500 with
>  drilled rotors that were not given to them for free as a
>  sponsorship deal.   Bet ya cant.
>
>
>  And..if its so good, why such small holes, and why so few?  (Cuz it
>  doesnt work)
>
>
>  On Fri, Apr 11, 2008 at 7:48 AM, Walker, Brian (Rich. Dist)
>  <Brian.Walker2 at vdot.virginia.gov> wrote:
>  > I had been told Porsche casts these features into their rotors. One
>  > would expect that a 6 figure car would have all the best in
>  > technology,  is the drilled/slotted feature one of those aesthetic
>  > things they throw  in?
>  >
>  >  I'd imagine cost from pad wear isn't of concern on those, maybe it's
>  > to  aid non-street pads on cars typically used on the street?
>  >
>  >
>  >  -----Original Message-----
>  >  From: Jeff Mohler [mailto:speedtoys.racing at gmail.com]
>  >  Sent: Friday, April 11, 2008 10:40 AM
>  >  To: Walker, Brian (Rich. Dist)
>  >
>  >
>  > Cc: Khalid Almufti; Supras at supras.com
>  >  Subject: Re: [Supras] stock brake rotors
>  >
>  >  On Fri, Apr 11, 2008 at 7:04 AM, Walker, Brian (Rich. Dist)
>  > <Brian.Walker2 at vdot.virginia.gov> wrote:
>  >  > I'm no expert but honestly, I don't think there is a performance
>  > gain
>  >
>  >  > from those type of rotors. Of course, with slots and drilling you
>  > are
>  >
>  >  > increasing surface area slightly, which would mean they can shed a
>
>  > > little more heat.
>  >  ---
>  >  Yes, you lose BRAKING surface area.
>  >
>  >  Nobody has proved that they make rotors cooler.  The goal is pad face
>
>  > temps, which go UP when you lose rotor surface area.
>  >
>  >  You're also decreasing contact area for the pad  >  slightly, which
>  > would mean a little less braking power (we're talking
>  >
>  >  > very small amounts)  >From the research I've done, pads nowadays
>  > don't
>  >
>  >  > release a gas layer  like they used to which was the main reason
>  > for  > slotting/drilling, to  remove or scrap that layer away. When
>  > you have  > a drilled/slotted piece  (provided it's added after
>  manufacturing vs.
>  >  > cast into the piece) you're  also adding areas prone to cracking.
>  >  ---
>  >  Drilled rotors crack no matter HOW the holes got there if you get
>  > enough  energy into them.  Its how a round piece of metal expands.
>  >  Has anyone ever seen any evidence of a rotor casting WITH holes?
>  >
>  >  No..it doesnt exist.
>  >
>  >  If you put holes in pizza dough, does it stop splitting as you expand
>
>  > it  on the outside edge?  No..thats how a round rotor expands, and
>  > fails  with enough energy thrown at it.
>  >
>  >
>  >  >  for street use, most people use slotted/drilled for street because
>
>  > > they  look cool. There are some processes out there like cryo
>  > treating
>  >
>  >  > that  are supposed to reduce the possibility of cracking, I've
>  > never  > tried  them though.
>  >  ---
>  >  Nope.   Cryo hardenes the rotor, which adds some lifetime to it, but
>  >  unless the rotor costs like $130, its not worth the $50 to do it.
>  >  It'll still fail the same way..its still steel.
>  >
>