Interesting info I picked up on another forum:
Did I waste my money on the AP racing slotted rotors??
Did I waste my money on the AP racing slotted rotors??
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Drilled/slotted rotors
- Thread starter Oyagi
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Yes and no. Slotted and cross drilled rotors definitely had the "gassing" notion in mind but that doesn't mean that they don't have other significant advantages. All things being equal, drilled rotors, run cooler and are lighter. Slotted rotors, with more mass than drilled, are a better heat soak. Both provide better initial bite than a plain rotor and constantly refresh the pad surface.
Some of the better brake manufacturers go through a lot of R&D to engineer the amount, size, and chamfer radius of drilled and slotted rotors. The exact amount of holes and slots take into account the size of the disc and internal venting.
FWIW, I've always had good success with slotted rotors. Though I've never tried drilled (maybe I will if I go the Brembo Indy route).
Some of the better brake manufacturers go through a lot of R&D to engineer the amount, size, and chamfer radius of drilled and slotted rotors. The exact amount of holes and slots take into account the size of the disc and internal venting.
FWIW, I've always had good success with slotted rotors. Though I've never tried drilled (maybe I will if I go the Brembo Indy route).
No you didn't, please critically think about what this guy is saying, that somehow man has developed a material that doesn't gas out. Basic science tells you that every material naturally or manmade has a maximum temperature where it changes states from whichever form it is currently in. A gas to a solid through temperature change, a solid to a gas when a temperature change occurs that is sufficient to cause the solid to change states. Now can we make a material that will not gas our under the operating temperatures of a brake rotor "sure" will it have the sufficient coefficient of friction with an interface with the selected rotor material? This can only be determined through quatntified testing under controlled testing not conjecture.
Hopefully I have given you enough information to determine the validity of this claim you have found. Oh and if you are curious my avatar has slotted rotors and will stop from 100MPH to 0 MPH in less than 1.2 seconds and I tune the pads to the temperature reached on a specific track.
slotted is better than drilled- it still gives you the benefits yet at 25% of stress concentration as caused by drilling. (any hole drilled increases stress in the material around it sixfold)
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- 2 September 2009
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haven't found a rotor yet that will NOT crack to some degree while stopping my 2900lb race car. I learned from experience that cross drilled and racing don't mix.
Virtually every race car I have seen, with the exception of F1, has slotted rotors.
Aren't these carbon/carbon brakes which have no need for slots just as was mentioned for F1. These are engineered for extreme temperatures with no warm up period as is necessary for ferrous rotors.
The shuttle uses the same technology to stop. I believe you can find information in the SAE papers on Carbon Industries white papers on chemical-physical decomposition processes that occur on brake pads that achieve 1000Degrees C temperatures. They also quantified this by using thermogravimetry,differential thermal analysis with image analysis using a scanning electron microscope if I remember the paper correctly.
In simpler terms quantified analysis of gassing of brake pads with a carbon composition.
The shuttle uses the same technology to stop. I believe you can find information in the SAE papers on Carbon Industries white papers on chemical-physical decomposition processes that occur on brake pads that achieve 1000Degrees C temperatures. They also quantified this by using thermogravimetry,differential thermal analysis with image analysis using a scanning electron microscope if I remember the paper correctly.
In simpler terms quantified analysis of gassing of brake pads with a carbon composition.
Many pad manufacturers still use clays and 'fillers' which under high temperatures still 'gas-out'. Performance Friction Brakes (PFC) uses high quality materials in their race pads that do not have this problem and do not require slots/holes to expel any gasses that can cause the pad to 'float' on that gass layer and not bite into the rotor.
Drilled rotors aren't really good for or used for anything more than looks and are much more prone to cracking than slotted or blanks. Slotted rotors do increase initial bite and brake torque slightly at the expense of increased pad wear since the slots act like a cheese-grater and constantly clean the surface of the pad (not as necessary with a good pad).
Most iron-disc racecars do use slotted rotors from straight to partial to banana/curved slots. Short of Tri-Point/Stoptech SWC TC, it's not common to see drilled rotors on racecars. Carbon brakes like that ALMS car pictured above do not use slotted or drilled because of the characteristics of the brakes (which don't work that well when cold). Those holes are more than likely wear indicators.
I do agree that for most applications, OEM 'blank' rotors are perfectly fine, and the pad makes a far greater difference than changing the rotor. Slotted are great and since probably no on on here is doing a 6, 12, 24, 25 hour racing, the increased wear of the slotted rotors are not an issue.
Drilled rotors aren't really good for or used for anything more than looks and are much more prone to cracking than slotted or blanks. Slotted rotors do increase initial bite and brake torque slightly at the expense of increased pad wear since the slots act like a cheese-grater and constantly clean the surface of the pad (not as necessary with a good pad).
Most iron-disc racecars do use slotted rotors from straight to partial to banana/curved slots. Short of Tri-Point/Stoptech SWC TC, it's not common to see drilled rotors on racecars. Carbon brakes like that ALMS car pictured above do not use slotted or drilled because of the characteristics of the brakes (which don't work that well when cold). Those holes are more than likely wear indicators.
I do agree that for most applications, OEM 'blank' rotors are perfectly fine, and the pad makes a far greater difference than changing the rotor. Slotted are great and since probably no on on here is doing a 6, 12, 24, 25 hour racing, the increased wear of the slotted rotors are not an issue.
Billy, when is PFC going to make a front/rear track pad for the NSX?
Race or street?
They already make street pads and i'm gonna be testing them soon.
I fully agree with the general opinion on drilled/slotted rotors 
Drilled:
a BIG no no for track use unless the holes are cast in like with OE Porsche. These also do develop hairline cracks but on these rotors usually don't lead to failure as WILL happen with drilled discs.
Slotted:
not needed with street use, however look nice and no real downsides, except perhaps a "grinding/humming" sound while braking.
For track use I do use them on my MR2 Turbo as I feel the pads stay "cleaner" with somewhat better "bite" as they are scraped off all the time.
I can recommend "cryo-treating" of the rotors.
I got a slotted rotor set treated this way and while I usually warp non-treated discs after using them for a few trackdays, the treated discs while they now do shudder a small amount, hold up considerably better.
Drilled:
a BIG no no for track use unless the holes are cast in like with OE Porsche. These also do develop hairline cracks but on these rotors usually don't lead to failure as WILL happen with drilled discs.
Slotted:
not needed with street use, however look nice and no real downsides, except perhaps a "grinding/humming" sound while braking.
For track use I do use them on my MR2 Turbo as I feel the pads stay "cleaner" with somewhat better "bite" as they are scraped off all the time.
I can recommend "cryo-treating" of the rotors.
I got a slotted rotor set treated this way and while I usually warp non-treated discs after using them for a few trackdays, the treated discs while they now do shudder a small amount, hold up considerably better.
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I have seen small gains in rotor longevity from cyro treatment of rotors in some Grand Am Koni racecars ive driven.
Modern rotors rarely 'warp' anymore. Most of the time it is due to uneven pad deposits from poor quality pads which is made worse by poor break-in procedures (which is not needed on higher quality pads).
Modern rotors rarely 'warp' anymore. Most of the time it is due to uneven pad deposits from poor quality pads which is made worse by poor break-in procedures (which is not needed on higher quality pads).
Not always true. Btw they change them out after every race. $$$$$$$$
Are these not carbon discs? Come on man, we're talking steel here right?
I have the NSX-R slotted rotors. They look good and basic physics tells you they will handle heat better. Agree it isnt needed for street, but it can't hurt and in the event you decide to try a track event they are there.
I figure if there were no value at all Honda wouldnt have put them on the R. You cant exactly accused the R of having "dress up only" parts!
I figure if there were no value at all Honda wouldnt have put them on the R. You cant exactly accused the R of having "dress up only" parts!
Are these not carbon discs? Come on man, we're talking steel here right?
these may be made of 'sintered metal'- basically a manufacturing method where powdered metal is compressed in the mold to form a shape and then heated to form the bond- no residual stresses vs. casting.
How does 'basic physics' tell you slotted rotors will handle heat better?
They are on the C6R ALMS GT1 car, i'm pretty sure they are carbon.
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Well... I figure that pads heat up and the heat needs to be vented. Drilled or slotted rotors are going to vent that heat better. Drilled will reduce the surface strength too much for heavy track use, so slotted seems like a good compromise. Unless Im missing something?
More surface area means better heat dissipation?
anyone mention that slotted and/or drilled rotors are great for letting water out in the rain?
Well yes... Greater surface area definitely means greater dissipation, but the heat also needs to be removed, no?
So the slotted rotors lose some surface area, but channel the heat out of the system faster.
I mean I could be wrong, but if so, I dont understand why Honda would put slotted rotors on the type-R. It certainly wasnt for looks as, on that car, they made crazy sacrifices for performance. I suppose it could be for weight, but it seems to me that a vented spinning surface would be more efficient at *removing* hot gas better than a smooth spinning surface. So I guess the question is if the surface area lost in slotting is made up for by the (presumed) increased efficiency in removing heat.
Re-read Post #9 about pad gassing and the different types of rotors. Slots don't function or really have much of an effect on cooling atall. Honda probably did it on the R for looks and slightly increased torque/bite.
I'm not sure if I would go as far as calling it a myth, but water evacuation is rarely ever a problem, plus it is very hard for water to get near the rotor in the first place and even if it did, rotors are almost never at a temp where they won't immediately evaporate any water that even gets near the rotor. So water evacuation isn't really a benefit.
Thats not really the point Im making though. No matter what, the brakes are converting energy to heat via friction in order to stop the car. That heat must be removed from the pad to keep it from breaking down.
The rotor performs that function. The larger the surface area of the rotor, the better it dissipates heat.
The thing is, the rotor must then radiate off the heat in order to not break down itself. Ceramic and carbon are great because they dont heat up easily.
Steel does. So the question is do the slots help the rotor vent off heat more efficiently. I believe they do because I think thermodynamics would cause the heated air coming off of the pad to fill the channels in the rotor and the channels in the rotor would create greater airflow to move that heat off.
Again, I could be wrong, but someone with a physics background would need to explain to me where and why.
And there is just absolutely no way at all the R has slotted rotors purely for looks. For weight possibly. But when they are worrying about the weight of a shift knob and ripping out the interior, they arent adding shit for looks. It would run counter to the mission statement of that car.
The rotor performs that function. The larger the surface area of the rotor, the better it dissipates heat.
The thing is, the rotor must then radiate off the heat in order to not break down itself. Ceramic and carbon are great because they dont heat up easily.
Steel does. So the question is do the slots help the rotor vent off heat more efficiently. I believe they do because I think thermodynamics would cause the heated air coming off of the pad to fill the channels in the rotor and the channels in the rotor would create greater airflow to move that heat off.
Again, I could be wrong, but someone with a physics background would need to explain to me where and why.
And there is just absolutely no way at all the R has slotted rotors purely for looks. For weight possibly. But when they are worrying about the weight of a shift knob and ripping out the interior, they arent adding shit for looks. It would run counter to the mission statement of that car.
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The rotor dissapates heat through its surface area and internal vanes that act like a pump pumping air through the rotor to cool it down. Ducting air to the rotor or inside of the center of the rotor greatly improve this function.
Heat is created by the friction between the pad and rotor and surface temperatures of the rotor can see over 1000*F. The better the rotor dissapated heat, the less the pad heats up. Under a heavy braking track like a street-circuit with no long straights and constant braking, the rotor dosnt have the chance to cool down, thus the heat generated from the pad isn't dissapated to the rotor as well. If this continues, you get pad and caliper heat soak and eventually boil the fluid.
Slots in the rotor increase "mu", increase bite, torque, and pad wear. ***this is the advantage/benefit you are so dearly searching for why Honda put slotted rotors on the R, that and its benefits with pads that contain poorer materials that 'gas-out'. I know how you are thinking but the few mm wide slots don't evacuate heat from the pad but through its sharp edge, acts like a cheese grater and increases 'mu'/bite. It is the rotor diameter, width, and internal vanes that affect cooling.
Under extreme street-circuits like we had in Koni Challenge in our Roush/Valvoline Mustang GT which weighs over 3,000lbs, ducting cool air to the caliper helped reduce heat soak since rules don't allow enough ducting to effectively cool the rotor to keep the pads and thus caliper/fluid in check on a track with such high braking demands and few straights to cool down the rotors between the braking zones.
I hope those examples help.
Heat is created by the friction between the pad and rotor and surface temperatures of the rotor can see over 1000*F. The better the rotor dissapated heat, the less the pad heats up. Under a heavy braking track like a street-circuit with no long straights and constant braking, the rotor dosnt have the chance to cool down, thus the heat generated from the pad isn't dissapated to the rotor as well. If this continues, you get pad and caliper heat soak and eventually boil the fluid.
Slots in the rotor increase "mu", increase bite, torque, and pad wear. ***this is the advantage/benefit you are so dearly searching for why Honda put slotted rotors on the R, that and its benefits with pads that contain poorer materials that 'gas-out'. I know how you are thinking but the few mm wide slots don't evacuate heat from the pad but through its sharp edge, acts like a cheese grater and increases 'mu'/bite. It is the rotor diameter, width, and internal vanes that affect cooling.
Under extreme street-circuits like we had in Koni Challenge in our Roush/Valvoline Mustang GT which weighs over 3,000lbs, ducting cool air to the caliper helped reduce heat soak since rules don't allow enough ducting to effectively cool the rotor to keep the pads and thus caliper/fluid in check on a track with such high braking demands and few straights to cool down the rotors between the braking zones.
I hope those examples help.
Are these not carbon discs? Come on man, we're talking steel here right?
http://www.youtube.com/watch?v=ZaSL03K3bg4
