Slotted/Drilled/Slotted & Drilled --- Benefits??
#1
11-05-2012, 07:44 PM
Slotted/Drilled/Slotted & Drilled --- Benefits??
I just installed a big brake akebono caliper kit with slotted and drilled rotors. I went to SEMA this year and the guys from Brembo said slotted and drilled rotors are the worst of both worlds so to speak:icon 27: I was wondering what are the benefits of each kind? (Slotted/Drilled/Slotted&Drilled)
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#3
11-05-2012, 09:00 PM
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#4
11-06-2012, 03:08 AM
Brembo is right if your talking about track situations. Drilled and slotted reduces the structural integratity of the rotors. On the street, you'll never crack them but certain cheaper rotors have been known to crack under heavy track situations.
Most track heavy people recommend just sticking with blanks. In the past drilled and sloted helped cool the rotors and pads but with the amount of engineering that goes into even low end cars like civics and such these days there benefits are negated.
Even civics have the under body panels that funnels air to the brakes to cool them. Most modern cars too.
In essence there just for looks now. If you track a lot, i would stick with blanks if its only street go for the drilled and slotted if you like the looks.
Most track heavy people recommend just sticking with blanks. In the past drilled and sloted helped cool the rotors and pads but with the amount of engineering that goes into even low end cars like civics and such these days there benefits are negated.
Even civics have the under body panels that funnels air to the brakes to cool them. Most modern cars too.
In essence there just for looks now. If you track a lot, i would stick with blanks if its only street go for the drilled and slotted if you like the looks.
#5
11-07-2012, 12:01 AM
There are no benefits to having cross drilled and slotted rotors together. Cross drilled help to keep the rotors cool, resist brake fade and the keep the rotors from warping. Slots in the rotors help to heat the rotors up and get them at normal operating temps much quicker, the slots also shave a small layer of the pads away to ensure a fresh pad surface when clamping down on the rotor but they also reduce pad life as well. Slots and cross drilled on both rotors cancel each other out (one wants to cool the rotor down and the other wants to heat the rotor up). Plus you'll never see a race car with both cross drilled and slotted rotors, it's either one or the other. Just my two cents, (now I'm broke)...jk
#6
11-07-2012, 01:03 AM
I haven't been able to find anything reliable on slotted rotors in my limited searching.
There was one SAE white paper in 2006 i think from GM about cross drilled rotors.The Effect of Rotor Crossdrilling on Brake Performance
I don't remember where I read the full paper, but IIRC their end results was that at higher operating temperature and heavier use (ie track conditions), the cross drilled rotors developed significantly less heat and produced significantly more stopping power, but had increased brake pad wear and was structurally weaker. And at lower temperature (street conditions) there was no difference.
I think the biggest reasons why most people who track get the cheapest blanks they can find, is that 1) rotors wear out super fast at the track with track pads and track conditions. You don't want to be shelling out for expensive rotors every year for marginal improvements, and 2) brake fade is better than brake failure. Brake fade from heat is usually progressive and you can adjust your braking distances appropriately, whereas a cracked rotor at the very least means the end of your track weekend, and sometimes means getting intimately acquainted with a wall or tire barrier. most people just go the route of getting higher and higher temperature rated brake pads before thinking of shelling out for bling bling rotors.
I've never heard about slots on rotors heating up the rotors quicker, that would be against everything people would want out of the brake system. I've only heard people talk about some mythical gas boundary layer or something, but never any real tests.
There was one SAE white paper in 2006 i think from GM about cross drilled rotors.The Effect of Rotor Crossdrilling on Brake Performance
I don't remember where I read the full paper, but IIRC their end results was that at higher operating temperature and heavier use (ie track conditions), the cross drilled rotors developed significantly less heat and produced significantly more stopping power, but had increased brake pad wear and was structurally weaker. And at lower temperature (street conditions) there was no difference.
I think the biggest reasons why most people who track get the cheapest blanks they can find, is that 1) rotors wear out super fast at the track with track pads and track conditions. You don't want to be shelling out for expensive rotors every year for marginal improvements, and 2) brake fade is better than brake failure. Brake fade from heat is usually progressive and you can adjust your braking distances appropriately, whereas a cracked rotor at the very least means the end of your track weekend, and sometimes means getting intimately acquainted with a wall or tire barrier. most people just go the route of getting higher and higher temperature rated brake pads before thinking of shelling out for bling bling rotors.
I've never heard about slots on rotors heating up the rotors quicker, that would be against everything people would want out of the brake system. I've only heard people talk about some mythical gas boundary layer or something, but never any real tests.
Last edited by totopo; 11-07-2012 at 01:20 AM. Reason: added paper link
#7
11-07-2012, 02:11 PM
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#8
11-07-2012, 02:35 PM
The best for professional track use is drilled and slotted given the theoretical performance. The best for recreational track use is slotted. The best for street is plain.
Drilled/Slotted is only good if you keep the temp's consistent. Slotted can take the change from hot to cold much better. I get slotted only, for my usage.
Drilled/Slotted is only good if you keep the temp's consistent. Slotted can take the change from hot to cold much better. I get slotted only, for my usage.
#9
11-07-2012, 03:25 PM
#10
11-07-2012, 05:40 PM
There are many claims as to the benefits of drilled vs slotted rotors on stopping power. This guide is intended to provide some facts about drilled and slotted rotors. As a member of the SAE (Society of Automotive Engineers), I was pleased to see a paper "The Effect of Rotor Crossdrilling on Brake Performance" by two GM engineers published in 2006. They examined three vehicle platforms with cross-drilled rotors vs standard rotors to measure convection cooling capability, fade characteristics, wet braking, pedal feel and lining wear. The result is summarized as follows:
For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.
For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.
Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.
Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.
The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.
For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.
For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.
Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.
Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.
The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.
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