drilled and slotted rotors
07-25-2006, 04:34 PM
#3
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RE: drilled and slotted rotors
This is from an old thread:
ORIGINAL: CrazyAl
"Powerslot" rotors are basically a gimmick. The only REAL brake rotor upgrade is a larger diameter rotor, which is the "real deal". Don't waste your money on stock-size rotors.
Slots and Holes are commnly percieved as required on performance brakes. That isn't true. Many years ago (up through the 70's) brake pad technology wasn't so good, pad glazing and outgassing became a problem. Slots were invented to fix those problems. However, with modern pads, this isn't an issue. Holes are sometimes used on racing brakes in order to reduce the rotating weight of the caliper. However, holes and slots actually REDUCE the heat capacity of the brake disc, and create stress risers where cracks are more likely to form.
This comes from Wilwood's web site:
I wrote this in an older thread:
Don't get me wrong, good pads and stainless lines are a good (though basic) upgrade. But don't waste your money on the powerslot rotors.
"Powerslot" rotors are basically a gimmick. The only REAL brake rotor upgrade is a larger diameter rotor, which is the "real deal". Don't waste your money on stock-size rotors.
Slots and Holes are commnly percieved as required on performance brakes. That isn't true. Many years ago (up through the 70's) brake pad technology wasn't so good, pad glazing and outgassing became a problem. Slots were invented to fix those problems. However, with modern pads, this isn't an issue. Holes are sometimes used on racing brakes in order to reduce the rotating weight of the caliper. However, holes and slots actually REDUCE the heat capacity of the brake disc, and create stress risers where cracks are more likely to form.
This comes from Wilwood's web site:
Caution on drilled rotors: There is a common mis-perception that rotors are drilled to improve cooling. The reduced mass of a drilled rotor will dissipate its retained heat quicker, but it also builds up heat at a much faster rate. The decision to use drilled rotors should be solely based on the merits of the lower rotating and unsprung weight, and not for improved cooling. It is not wise to use drilled rotors in sustained high heat on hard braking tracks unless the team budget affords a high frequency of rotor and brake pad replacement.
I wrote this in an older thread:
Irotors look nice, but I would consider them a cosmetic upgrade ONLY.
Braking power (brake torque) is affected by four things:
1) Line pressure
2) Coefficient of Friction of the brake pad (composition of the pad)
3) Diameter of the rotor
4) Clamping strength of the calipers
Upgrading to "aftermarket rotors" that are stock-size, such as the "powerstop rotors" or the Irotors changes none of these.
1) Line pressure can be improved by using a different diameter Master Cylinder (bad for our cars becasue it screws with the ABS system), or by installing stiffer brake lines, such as the braided stainless lines that were mentioned earlier. This is a good, but relatively minor, mod.
2) "Race" style brake pads have a higher coefficient of friction. This is a great bang-for-your buck upgrade becasue it's cheap and easy to install--another good, but still minor mod. The downside is that these "race" pads usually wear out faster, and many also wear out your rotors faster.
3) Larger diameter rotors are one of the best possible mods--I would say the #1 brake mod. The larger rotors offer better brake torque AND better cooling for reduce fade. This makes a major difference in performance. Unfortunatley, larger rotors are expensive and they usually require a lot of "accessory" hardware like new calipers or at least caliper brackets.
4) Upgraded calipers tend to have a stiffer construction and also more piston surface area. This lets them clamp harder. Like #3 this is a major upgrade, but with similar complexity. Upgraded calipers often require new bracketry, hoses, and so forth.
That being said, any sort of SERIOUS brake upgrade is going to consist of larger rotors, better calipers, and hopefully some good pads & lines to go with it. I agree with the earlier recommendations of Brembo, Wilwood, and Baer. Those are the brands (especially the first two) that you see on REAL "cost-no-object" race cars. That "serious" of a system might not be needed if you just want nice looking parts for your show car or a minor upgrade for fun on the street. But I would be very wary of a product that claimed "enhanced brake performance" that didn't offer at least an oversized pair of rotors and the appropriate bracketry. Comparing a "pads and lines" upgrade to a real brake upgrade like a Baer or Wilwood 14" disc package is like comparing a Toyota Camry to a Ferrari. (With the price difference to match, unfortunately).
Braking power (brake torque) is affected by four things:
1) Line pressure
2) Coefficient of Friction of the brake pad (composition of the pad)
3) Diameter of the rotor
4) Clamping strength of the calipers
Upgrading to "aftermarket rotors" that are stock-size, such as the "powerstop rotors" or the Irotors changes none of these.
1) Line pressure can be improved by using a different diameter Master Cylinder (bad for our cars becasue it screws with the ABS system), or by installing stiffer brake lines, such as the braided stainless lines that were mentioned earlier. This is a good, but relatively minor, mod.
2) "Race" style brake pads have a higher coefficient of friction. This is a great bang-for-your buck upgrade becasue it's cheap and easy to install--another good, but still minor mod. The downside is that these "race" pads usually wear out faster, and many also wear out your rotors faster.
3) Larger diameter rotors are one of the best possible mods--I would say the #1 brake mod. The larger rotors offer better brake torque AND better cooling for reduce fade. This makes a major difference in performance. Unfortunatley, larger rotors are expensive and they usually require a lot of "accessory" hardware like new calipers or at least caliper brackets.
4) Upgraded calipers tend to have a stiffer construction and also more piston surface area. This lets them clamp harder. Like #3 this is a major upgrade, but with similar complexity. Upgraded calipers often require new bracketry, hoses, and so forth.
That being said, any sort of SERIOUS brake upgrade is going to consist of larger rotors, better calipers, and hopefully some good pads & lines to go with it. I agree with the earlier recommendations of Brembo, Wilwood, and Baer. Those are the brands (especially the first two) that you see on REAL "cost-no-object" race cars. That "serious" of a system might not be needed if you just want nice looking parts for your show car or a minor upgrade for fun on the street. But I would be very wary of a product that claimed "enhanced brake performance" that didn't offer at least an oversized pair of rotors and the appropriate bracketry. Comparing a "pads and lines" upgrade to a real brake upgrade like a Baer or Wilwood 14" disc package is like comparing a Toyota Camry to a Ferrari. (With the price difference to match, unfortunately).
07-25-2006, 04:56 PM
#5
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RE: drilled and slotted rotors
I have to disaagree that powerslots are a gimmick....i put then on 2 different vehicles with Hawk pads..and i could tell a huge differance ...was it just the pads... i dont think so... one ona Nisasn Sentra the othere a Jeep...they both performed better...i think its a nice economical upgrade with the right pads of course... JMO
07-25-2006, 07:19 PM
#7
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RE: drilled and slotted rotors
Torch, I have no doubt that your "brake upgrade" gave you better braking performance.
But, that being said, I'll bet good money that 95% of your improvement came from the pads and very little from the rotors. You would see nearly identical performance from JUST the pad swap.
But, that being said, I'll bet good money that 95% of your improvement came from the pads and very little from the rotors. You would see nearly identical performance from JUST the pad swap.
07-25-2006, 08:44 PM
#8
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RE: drilled and slotted rotors
i have irotors, and i notice significant improvement (along with hawk pads). however, the difference is NOT noticeable until the brakes get really hot. when they are cool, they feel a little spongy but grip equally well as stock. when they get hot, they give the abs system a hell of a work out and the car just STOPS.
07-26-2006, 03:22 PM
#9
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RE: drilled and slotted rotors
This also from the same old post:
I don't understand how you can say this. Do you really know what they are about and how they work? First of all the Power Slot rotors are premuim rotors, not some cheap off shore castings. They really do work in helping with brake fade and cooling. Your average brake pad, including the so called "Perf. Ceramic" start out-gassing around 400-500 degrees. Now reaching this temp. is Not hard to do when it comes to aggressive braking.....spirited back canyon driving for example. Now you can help the situation by using a better pad, such as the Hawk HPS pads. These pads have a good initial bite fom cold.. say 0 degrees all the way to their 800 degree out-gassing. The Power Slot rotors are designed to evacuate/escape the gasses from between pad and rotor.
( Where brake fade comes from) When you combine these two, power slot rotors and Hawk pads you get excellent braking repeatability for a street car. As far as the "cryo" goes, I beleive it helps. How much I don't know. The NASCAR boys have been using it for years with rear-end and tranny gears, etc.
There you go, I will get off my soap box now. No intentions on stepping on toes.
quote:
ORIGINAL: CrazyAl
"Powerslot" rotors are basically a gimmick. The only REAL brake rotor upgrade is a larger diameter rotor, which is the "real deal". Don't waste your money on stock-size rotors.
quote:
I don't understand how you can say this. Do you really know what they are about and how they work? First of all the Power Slot rotors are premuim rotors, not some cheap off shore castings. They really do work in helping with brake fade and cooling. Your average brake pad, including the so called "Perf. Ceramic" start out-gassing around 400-500 degrees. Now reaching this temp. is Not hard to do when it comes to aggressive braking.....spirited back canyon driving for example. Now you can help the situation by using a better pad, such as the Hawk HPS pads. These pads have a good initial bite fom cold.. say 0 degrees all the way to their 800 degree out-gassing. The Power Slot rotors are designed to evacuate/escape the gasses from between pad and rotor.
( Where brake fade comes from) When you combine these two, power slot rotors and Hawk pads you get excellent braking repeatability for a street car. As far as the "cryo" goes, I beleive it helps. How much I don't know. The NASCAR boys have been using it for years with rear-end and tranny gears, etc.
There you go, I will get off my soap box now. No intentions on stepping on toes.
quote:
ORIGINAL: CrazyAl
"Powerslot" rotors are basically a gimmick. The only REAL brake rotor upgrade is a larger diameter rotor, which is the "real deal". Don't waste your money on stock-size rotors.
quote:
07-26-2006, 05:22 PM
#10
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RE: drilled and slotted rotors
I didn't want to get into the nitty gritty here, but seeing as how this has been raised again, I will. I spent two years running a brake dyno in a mechanical testing lab while I was in grad school, this is one area where I know my stuff.
1) Pad outgassing is something that people love to bring up but it is both misunderstood and rare. Outgassing happens when the binding agents ("glue") that holds a brake pad composite together starts to turn into gas when the pads get hot. This "gas" can sometimes form a very thin "pad" between the surface of the rotor and the pad itself, reducing the friction between the two, which in turn reduces brake torque.
First off, outgassing is primarily an OLD problem which has essentially been eliminated since the 80's with better pad composition. While outgassing technically does occurr these days, it is minor enough that most people, even competitive drivers, wouldn't notice.
Second, outgassing has nothing to do with brake fade. (Fade occurs when the pads and rotors become too hot, which in turn lowers the coefficient of friction of the iron rotor and the metallic particles in the pads--it has nothing to do with gassing).
Third, outgassing is generally only a problem with a brand new set of brake pads. Once they are heat cycled a few times all of the low-volatile organic binders in the pads have already outgassed and they are simply "done". Further heating won't do anything becasue the source of the gas is "used up". This is why all the major aftermarket brake companies recommend that you "bed" or "season" your pads before seriously using them in race applications. Pads don't have a "bottomless pit" of "gas" that spews forth every time they get hot. There is only so much of that material present in the pads, and it goes away very quickly. Once it's gone, it's gone.
2) Slotted rotors can reduce the effects of outgassing. However, most so-called "performance rotors" are simply leaning on this very small "benefit" in order to hype up a new rotor.
I don't doubt that some aftermarket rotors are of high quality. However, don't knock OEM. All the major auto makers have very seriously engineered their brakes. A brake problem would be a financial catastrophe with the recalls, lawsuits, and lost sales that would follow. Consequently they have hordes of engineers and sophsiticated labs that work on these products. Perhaps the end product is made in China or Korea or wherever...but that doesn't mean that it's not a solid part, and it still has to meet spec before they are put on your car.
People claim that their aftermarket rotors are somehow "better" than stock, but HOW exactly? The answer is that most of the time, they are no better or they hype up a very minor "benefit" as if it was the next big thing in brake design. For example, powerslot loves to mention that their rotors are plated. So what? The brake pads will strip off the plating layer after your first stop anyway. Other companies paint the "hat" area of the rotor. Again, they look nice, sure, but that paint isn't really visible and it's not giving you any extra performance.
The ONLY thing that I can think of that someone might do to a stock-size rotor that would make it honestly better than stock would be if they converted a "straight vane" rotor to a directional vane rotor (assuming they could keep the material thicknesses correct at the same time). A direcitonal-vane rotor is more efficient at cooling itself than a straight-vane rotor. Therefore, such a product would be more resistant to fade. However, the brake torque would be no better than stock. I have also seen "heavy duty" rotors, such as the Powerslots, which have thicker iron which entails smaller cooling channels. This is a trade off. The discs heat up slower, but they cool down slower as well. I'd rather stick with what the manufacturer specified.
As I said earlier, I belive 100% you guys that installed these aftermarket brake kits and got better performance out of it. But, I would put 95% of the improvement on the pads and very little on the rotors. Next time, try just the pads. If you're not happy and the money is still burning a hole in your pocket, then by all means buy the rotors too.
If you want to learn more about this, I suggest the following books:
Clutches and Brakes by Orthwein
Brake Design and Safety by Limpert
Advanced Brake Technology, published by SAE (I can't recall the author, sorry).
1) Pad outgassing is something that people love to bring up but it is both misunderstood and rare. Outgassing happens when the binding agents ("glue") that holds a brake pad composite together starts to turn into gas when the pads get hot. This "gas" can sometimes form a very thin "pad" between the surface of the rotor and the pad itself, reducing the friction between the two, which in turn reduces brake torque.
First off, outgassing is primarily an OLD problem which has essentially been eliminated since the 80's with better pad composition. While outgassing technically does occurr these days, it is minor enough that most people, even competitive drivers, wouldn't notice.
Second, outgassing has nothing to do with brake fade. (Fade occurs when the pads and rotors become too hot, which in turn lowers the coefficient of friction of the iron rotor and the metallic particles in the pads--it has nothing to do with gassing).
Third, outgassing is generally only a problem with a brand new set of brake pads. Once they are heat cycled a few times all of the low-volatile organic binders in the pads have already outgassed and they are simply "done". Further heating won't do anything becasue the source of the gas is "used up". This is why all the major aftermarket brake companies recommend that you "bed" or "season" your pads before seriously using them in race applications. Pads don't have a "bottomless pit" of "gas" that spews forth every time they get hot. There is only so much of that material present in the pads, and it goes away very quickly. Once it's gone, it's gone.
2) Slotted rotors can reduce the effects of outgassing. However, most so-called "performance rotors" are simply leaning on this very small "benefit" in order to hype up a new rotor.
I don't doubt that some aftermarket rotors are of high quality. However, don't knock OEM. All the major auto makers have very seriously engineered their brakes. A brake problem would be a financial catastrophe with the recalls, lawsuits, and lost sales that would follow. Consequently they have hordes of engineers and sophsiticated labs that work on these products. Perhaps the end product is made in China or Korea or wherever...but that doesn't mean that it's not a solid part, and it still has to meet spec before they are put on your car.
People claim that their aftermarket rotors are somehow "better" than stock, but HOW exactly? The answer is that most of the time, they are no better or they hype up a very minor "benefit" as if it was the next big thing in brake design. For example, powerslot loves to mention that their rotors are plated. So what? The brake pads will strip off the plating layer after your first stop anyway. Other companies paint the "hat" area of the rotor. Again, they look nice, sure, but that paint isn't really visible and it's not giving you any extra performance.
The ONLY thing that I can think of that someone might do to a stock-size rotor that would make it honestly better than stock would be if they converted a "straight vane" rotor to a directional vane rotor (assuming they could keep the material thicknesses correct at the same time). A direcitonal-vane rotor is more efficient at cooling itself than a straight-vane rotor. Therefore, such a product would be more resistant to fade. However, the brake torque would be no better than stock. I have also seen "heavy duty" rotors, such as the Powerslots, which have thicker iron which entails smaller cooling channels. This is a trade off. The discs heat up slower, but they cool down slower as well. I'd rather stick with what the manufacturer specified.
As I said earlier, I belive 100% you guys that installed these aftermarket brake kits and got better performance out of it. But, I would put 95% of the improvement on the pads and very little on the rotors. Next time, try just the pads. If you're not happy and the money is still burning a hole in your pocket, then by all means buy the rotors too.
If you want to learn more about this, I suggest the following books:
Clutches and Brakes by Orthwein
Brake Design and Safety by Limpert
Advanced Brake Technology, published by SAE (I can't recall the author, sorry).