Not so Hot Brakes
06-26-2004, 12:19 AM
#16
Race Director
I am with you Tomas, I dont think drilled rotors is for looks. I mean, its not like they look cool anyway! They are just holes! I have drilled rotors and they work great over the stock I had.
06-26-2004, 02:05 AM
#17
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Thread Starter
Thank you for all the feedback and wealth of opinions. I’ll respond to them slowly one by one.
The rotors are mounted correctly. They are Zimmerman from Paragon and the “unidirectional” drill pattern also confused me initially, but is really irrelevant for the rotation direction. Inside are 40 straight radial vanes (channels) with one axial hole each (from both sides), i.e. 40 holes from each side at four different radii.
The holes in the rear rotors (also Zimmerman) are in a more intricate bidirectional pattern. Maybe Zimmerman got tired of having to explaining to customers that they do not need specific left and right discs.
Since the rotor really is a radial fan and the volume is ever expanding as a function of the radial distance, the inside has a lower pressure that the outside, therefore the flow is from the outside in through the cross drilled holes. This however may not be true if the ducting to the inner radius provides a high enough pressure.
streckfu's951, Thanks for the picture upload instructions. I think I understand, but you don’t appear to address uploading multiple pictures from a hard drive, which was my gripe. Thinking about it though, it probably is an option to upload photos to the Rennlist photos and then make references to that.
The propensity for cracking on drilled rotors must be a function of hole size and I am sure is caused by a thermal gradient induced excessive stress. It is therefore interesting to note, that the holes on the hotter front (Zimmerman) rotors are smaller than those on the rear. I just discovered that my original non-drilled rear rotors both had hairline cracks, so this side-effect is not exclusive for drilled discs.
With the current mounting method the heat-sinks will stay in place for more than the lifetime of the discs only requiring occasional inspection for corrosion in the area of the spring attachment. No, they will not fly off, that’s ridiculous. Just to give you a sense of proportions: the heat-sink half-shell weighs 90g, are mounted on a diameter of 6.5” and the wheel rotates about 2250 rpm at 160 mph.
Yes, my old fluid looked pretty ugly, when I changed to ATE Gold and already made a successful preliminary test for boiling with the new fluid.
Laust
The rotors are mounted correctly. They are Zimmerman from Paragon and the “unidirectional” drill pattern also confused me initially, but is really irrelevant for the rotation direction. Inside are 40 straight radial vanes (channels) with one axial hole each (from both sides), i.e. 40 holes from each side at four different radii.
The holes in the rear rotors (also Zimmerman) are in a more intricate bidirectional pattern. Maybe Zimmerman got tired of having to explaining to customers that they do not need specific left and right discs.
Since the rotor really is a radial fan and the volume is ever expanding as a function of the radial distance, the inside has a lower pressure that the outside, therefore the flow is from the outside in through the cross drilled holes. This however may not be true if the ducting to the inner radius provides a high enough pressure.
streckfu's951, Thanks for the picture upload instructions. I think I understand, but you don’t appear to address uploading multiple pictures from a hard drive, which was my gripe. Thinking about it though, it probably is an option to upload photos to the Rennlist photos and then make references to that.
The propensity for cracking on drilled rotors must be a function of hole size and I am sure is caused by a thermal gradient induced excessive stress. It is therefore interesting to note, that the holes on the hotter front (Zimmerman) rotors are smaller than those on the rear. I just discovered that my original non-drilled rear rotors both had hairline cracks, so this side-effect is not exclusive for drilled discs.
With the current mounting method the heat-sinks will stay in place for more than the lifetime of the discs only requiring occasional inspection for corrosion in the area of the spring attachment. No, they will not fly off, that’s ridiculous. Just to give you a sense of proportions: the heat-sink half-shell weighs 90g, are mounted on a diameter of 6.5” and the wheel rotates about 2250 rpm at 160 mph.
Yes, my old fluid looked pretty ugly, when I changed to ATE Gold and already made a successful preliminary test for boiling with the new fluid.
Laust
06-26-2004, 02:42 AM
#18
Rennlist Member
Hey Laust
4) "Brake pads. Using different pads does not change the heat generated, but some pads generate more friction-reducing gas/dust than others, increasing the pedal pressure (fading). The ones I used (don’t know the brand, 30% left when finished) faded more in the beginning, probably being de-gassed with use. They don’t grind the rotors down as some pads do. I have tried Mintex and found them to need too much pressure for street use."
I am by no means a brake expert ... Although I had toasted a pair of almost brand new S4 rotors ... at that time about a $500.00 blunder. I was told that the reason they toasted ( i was getting a soft peddle ) was due to the pad I was using, for the track I was at. As soon as I switched to porsche green pads, I never had a braking problem again .... But like I said I am not
expert ...
Oh BTW when I cooked those rotors they got so hot that I badly burned my hand on the club sport wheel and the temp got so hot that it change the anodized wheel to a crackle gold cast ... Yep I fried'em
Good luck
regards
Ed
4) "Brake pads. Using different pads does not change the heat generated, but some pads generate more friction-reducing gas/dust than others, increasing the pedal pressure (fading). The ones I used (don’t know the brand, 30% left when finished) faded more in the beginning, probably being de-gassed with use. They don’t grind the rotors down as some pads do. I have tried Mintex and found them to need too much pressure for street use."
I am by no means a brake expert ... Although I had toasted a pair of almost brand new S4 rotors ... at that time about a $500.00 blunder. I was told that the reason they toasted ( i was getting a soft peddle ) was due to the pad I was using, for the track I was at. As soon as I switched to porsche green pads, I never had a braking problem again .... But like I said I am not
expert ...
Oh BTW when I cooked those rotors they got so hot that I badly burned my hand on the club sport wheel and the temp got so hot that it change the anodized wheel to a crackle gold cast ... Yep I fried'em
Good luck
regards
Ed
06-30-2004, 09:08 PM
#19
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Thread Starter
Pekster:
“Looks like that heat conducting paste is going to migrate onto the pads when things heat up, no?
The migrating paste was something I didn’t consider and sure enough a few droplets do migrate to the friction area (outside only), but I have been unable to detect any friction reduction. Furthermore the supply is very finite.
Ahmet:
“Cross drilling came up last time, if you do research, you will see that it's not helpful for what you're trying to do.”
If you by research mean gauge the opinions, then I would say it is 50/50 pro et con for drilled rotors. Meanwhile when it comes to physics and solid engineering the facts are independent of opinions and that is what I am trying to get at, knowing well that I also start out with a set of opinions, but usually supported by a number of observations and theoretical knowledge.
Red944:
“Did you do temp tests after every step?”
I intended to do that, but realized that the effort would be quite substantial. Measuring the temperature is also quite tricky. How should the brakes be heated up? When have the brakes reached thermal equilibrium (calorie influx rate equals outflux)? Where on the brakes should the temperature be measured? I measured the max spatial temperature, which was on the root of the disc.
So if the benefit is small it may drown in the measurement “noise”.
Rich Sandor:
“Um. why would you want to insulate the wheel from the brakes, when you can use it as a giant heat sink??? If anything I would sand down the paint on the back of the wheel and put conductive grease on it.”
I fully agree about using the wheels to the fullest as a giant heat sink and have made no attempts to thermally isolate them.
Tomas:
“One problem with a street driven car is that rust forms inside the disc vanes and drastically reduce heat transfer. I've sand blasted the vanes in the disc with decent result.”
Good point, I applied a thin coat of high temp black paint on inside as well for the dual purpose of extra heat radiation and some rust protection.
Ed:
“As by drilling you would lose what would otherwise be braking surface area ...
Also there are a few companies that offer Heat Emitting coatings like the ones
you had mentioned in the thread on coatings (that would be for the calipers)”
I am not sure what you mean by losing braking surface area. Aftermarket clutch manufacturers have no qualms about reducing the friction area. It cost in lifespan and in this case rotor lifespan, that’s all. If you mean losing cooling area by the area of the vent holes, then that is more than gained back by the increased surface area by the depth of the holes and added airflow.
Professionally applied Heat Emitting coatings may be slightly better that paint, but I am deliberately trying to use sensible low cost means. An alternative to all these suggestions is obviously “getting it over with” by buying a set of “Big Reds” or vented ceramic brakes a la Carrera GT.
Laust
“Looks like that heat conducting paste is going to migrate onto the pads when things heat up, no?
The migrating paste was something I didn’t consider and sure enough a few droplets do migrate to the friction area (outside only), but I have been unable to detect any friction reduction. Furthermore the supply is very finite.
Ahmet:
“Cross drilling came up last time, if you do research, you will see that it's not helpful for what you're trying to do.”
If you by research mean gauge the opinions, then I would say it is 50/50 pro et con for drilled rotors. Meanwhile when it comes to physics and solid engineering the facts are independent of opinions and that is what I am trying to get at, knowing well that I also start out with a set of opinions, but usually supported by a number of observations and theoretical knowledge.
Red944:
“Did you do temp tests after every step?”
I intended to do that, but realized that the effort would be quite substantial. Measuring the temperature is also quite tricky. How should the brakes be heated up? When have the brakes reached thermal equilibrium (calorie influx rate equals outflux)? Where on the brakes should the temperature be measured? I measured the max spatial temperature, which was on the root of the disc.
So if the benefit is small it may drown in the measurement “noise”.
Rich Sandor:
“Um. why would you want to insulate the wheel from the brakes, when you can use it as a giant heat sink??? If anything I would sand down the paint on the back of the wheel and put conductive grease on it.”
I fully agree about using the wheels to the fullest as a giant heat sink and have made no attempts to thermally isolate them.
Tomas:
“One problem with a street driven car is that rust forms inside the disc vanes and drastically reduce heat transfer. I've sand blasted the vanes in the disc with decent result.”
Good point, I applied a thin coat of high temp black paint on inside as well for the dual purpose of extra heat radiation and some rust protection.
Ed:
“As by drilling you would lose what would otherwise be braking surface area ...
Also there are a few companies that offer Heat Emitting coatings like the ones
you had mentioned in the thread on coatings (that would be for the calipers)”
I am not sure what you mean by losing braking surface area. Aftermarket clutch manufacturers have no qualms about reducing the friction area. It cost in lifespan and in this case rotor lifespan, that’s all. If you mean losing cooling area by the area of the vent holes, then that is more than gained back by the increased surface area by the depth of the holes and added airflow.
Professionally applied Heat Emitting coatings may be slightly better that paint, but I am deliberately trying to use sensible low cost means. An alternative to all these suggestions is obviously “getting it over with” by buying a set of “Big Reds” or vented ceramic brakes a la Carrera GT.
Laust
06-30-2004, 09:29 PM
#20
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Rennlist Lifetime Member
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Maybe it's just me but I'm sitting here scratching my head...this seems like a lot of unneeded expense & effort. I use the OG Racing ducts, ATE fluid (I change every 3-4 track days), stock rotors (I have at least a dozen stacked in the garage) and have recently switched to Pagid pads (I used to use Hawk Blues but grew very tired of the corrosive dust).
I've run several 30-60 minute events this year (ie. Mid-Ohio w/ lap times around 1:46 and Putnam Park w/ lap times around 1:20); my lap times were within 1.5 seconds of this years top E Stock qualifiers at the PCA races this year.
I have yet to experience brake fade with this setup.
I've run several 30-60 minute events this year (ie. Mid-Ohio w/ lap times around 1:46 and Putnam Park w/ lap times around 1:20); my lap times were within 1.5 seconds of this years top E Stock qualifiers at the PCA races this year.
I have yet to experience brake fade with this setup.
