Whats the difference betwwen Slotted and Cross Driller Rotors?
Originally Posted by 98intrigue
the cross-drilled rotors have a problem of cracking.
from the stoptech website
For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.
For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.
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From: OC
true cross drilled rotors will not crack as they are casted with the holes in them already. if the cross drilled rotor was originally a blank that has holes in it, then they are more prone to cracking since the integrity of the metal will have changed now there are holes in it.
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slots can be thought of as little streams or ridges coming from the center of the plate outwards.
drilled holes are just that. a hole that is put through the metal from one side to the other.
the benefit in slots is that they hold the rigidity of the material better and therefore are less prone to cracking. track use or not I would probably suggest slotted and vented rotors to anyone thinking about going with cross drilled. the benefits for cooling on the cross drilled are not great enough to consider cross drilled as an viable option over slotted.
drilled holes are just that. a hole that is put through the metal from one side to the other.
the benefit in slots is that they hold the rigidity of the material better and therefore are less prone to cracking. track use or not I would probably suggest slotted and vented rotors to anyone thinking about going with cross drilled. the benefits for cooling on the cross drilled are not great enough to consider cross drilled as an viable option over slotted.
Rotors are not inherently strong because, contrary to the popular belief of many, they are not made of steel but of cast iron. Thus they do not have the structural strength of steel, and in fact can not only crack, but shatter to pieces (btw, that is real "bad" when it happens).
One of the tasks of the rotor, apart from being something for the calipers and pad to grab onto for the purpose of slowing the rotation of the wheel, is to absorb the heat that is generated from the friction of the braking action between the pad and the rotor surface. Cast iron does that very effectively.
Unfortunately, there is a limit to how much heat it can store, and in heavy braking situations, especially in a track scenario where you are on it hard multiple times per lap, you need to have a means of shedding heat from the rotor so that it does not overheat and lose its ability to efficiently brake by getting glazing on the surface between the pad and the rotor. One of the ways to increase dissipation of heat is to increase the surface area of the rotor which is in contact with air, and of course others are to increase the flow of air across the rotors with their design and even ducting of air flow (like blowing on your hot soup or pizza slice before you proceed to burn the roof of your mouth anyway).
Cross drilling your rotors does several positive and several negative things. On the positive it decreases unsprung weight (modestly), increases surface area for heat dissipation, provides for slightly better shedding of dust, and it looks really neat. On the negative it reduces the mass of metal available for absorption of heat and undeniably weakens the structure of the rotor. There are numerous tracks or types of motor sport events where they just will not let you run a cross drilled rotor. Maybe it is over reaction, but if you have ever seen a shattered cross drilled rotor and what happens to a car when it goes........
Slotted rotors provide the benefits of better shedding of dust, more mass for heat absorption, and no structural integrity declines, plus additional surface area for heat dissipation. Other advances over the years in brake pad compounds etc. have also helped.
So really there is no performance reason remaining to use a drilled rotor, and several to suggest one should not. But for street use and cool looks, it is absolutely fine.
The only negative is that folks who don't know (most of them) will see the cross drilled rotor and think "wow, that car has really powerful brakes" and those who really do know and are track snobs will think "wow, that guy either doesn't know what he is doing or is not serious about real performance".
You don't have to care about either of them, frankly. Do what you want, and like with the car and the brakes. It is your car. If some guy gives you hassle about the drilled rotors, just tell him you know exactly what you are doing, you like the looks and it is fine for the track a couple times a year, and way more than adequate for the street (If you run a BBK cross drilled rotor it is almost inconceivable that any kind of street demand is going to come anywhere near being stressful to that rotor).
One of the tasks of the rotor, apart from being something for the calipers and pad to grab onto for the purpose of slowing the rotation of the wheel, is to absorb the heat that is generated from the friction of the braking action between the pad and the rotor surface. Cast iron does that very effectively.
Unfortunately, there is a limit to how much heat it can store, and in heavy braking situations, especially in a track scenario where you are on it hard multiple times per lap, you need to have a means of shedding heat from the rotor so that it does not overheat and lose its ability to efficiently brake by getting glazing on the surface between the pad and the rotor. One of the ways to increase dissipation of heat is to increase the surface area of the rotor which is in contact with air, and of course others are to increase the flow of air across the rotors with their design and even ducting of air flow (like blowing on your hot soup or pizza slice before you proceed to burn the roof of your mouth anyway).
Cross drilling your rotors does several positive and several negative things. On the positive it decreases unsprung weight (modestly), increases surface area for heat dissipation, provides for slightly better shedding of dust, and it looks really neat. On the negative it reduces the mass of metal available for absorption of heat and undeniably weakens the structure of the rotor. There are numerous tracks or types of motor sport events where they just will not let you run a cross drilled rotor. Maybe it is over reaction, but if you have ever seen a shattered cross drilled rotor and what happens to a car when it goes........
Slotted rotors provide the benefits of better shedding of dust, more mass for heat absorption, and no structural integrity declines, plus additional surface area for heat dissipation. Other advances over the years in brake pad compounds etc. have also helped.
So really there is no performance reason remaining to use a drilled rotor, and several to suggest one should not. But for street use and cool looks, it is absolutely fine.
The only negative is that folks who don't know (most of them) will see the cross drilled rotor and think "wow, that car has really powerful brakes" and those who really do know and are track snobs will think "wow, that guy either doesn't know what he is doing or is not serious about real performance".
You don't have to care about either of them, frankly. Do what you want, and like with the car and the brakes. It is your car. If some guy gives you hassle about the drilled rotors, just tell him you know exactly what you are doing, you like the looks and it is fine for the track a couple times a year, and way more than adequate for the street (If you run a BBK cross drilled rotor it is almost inconceivable that any kind of street demand is going to come anywhere near being stressful to that rotor).
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From the Mercedes-Benz new SLK brochure:
"At first glance, those little holes may not seem like much. But in a high-performance braking situation where rotors can get red-hot and brake fluid can boil, the ability to dissipate heat and vapors is vital. Rather than simply drilling holes in the discs- a method that can cause 'stress risers' that weaken the metal- the perforations in the SLK front brakes are cast in place to help maintain maximum strength."
"At first glance, those little holes may not seem like much. But in a high-performance braking situation where rotors can get red-hot and brake fluid can boil, the ability to dissipate heat and vapors is vital. Rather than simply drilling holes in the discs- a method that can cause 'stress risers' that weaken the metal- the perforations in the SLK front brakes are cast in place to help maintain maximum strength."
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From: SOCAL
None of my cross-drilled rotors on my previous car ever cracked. I went through 2 sets and tracked the car often. Not to say that cross-drilled rotors can not crack, but you have to look for specific features. Be weary of drilled rotors that have an abundance of holes. The advantage cross drilled rotors have over slotted rotors is that they allow pads to outgas when they overheat. When pads overheat, they start to vaporize and this creates a layer of gas trapped between the pad and the rotor. This is typically the first type of fade most drivers run into, evidenced by a stiff pedal, but necessitating more force on the pedal to get the car to stop as effectively. slotted rotors can do very little to vent air. If this is such a problem that you need to add a lot of cross-drilling, then you need to reevaluate your pads and the rotor mass. Make sure the holes are drilled between the vains of the rotor and not just randomly. This can prevent structural problems. Also look for spiral and offset drilling. They should be drilled so that they are not in a straight line from the center of the rotor. And if you were to trace a line along the arc of any of the holes, ever other set of holes should be along the same arc. Lastly, you want to make sure the holes are radiused. Cracking in any metal occurs at sharp points(corners). Radiusing the holes will reduce the chances of a crack starting at a hole in the the rotor's surface(where the heat is always highest).
My last car used Cross-drilled rotors sold by Stillen. They had all of these traits. It should be important to mention that it was a 240sx running on 300ZX brakes. Running large enough brakes are very important to any rotor. I would never use cross-drilling as a fix for any braking problem. Below is a photos of the rotors I used:
http://www.stillen.com/product_images/NIS3000_f.jpg
Notice there is only one hole per rotor vane and located between the vanes. The radius pattern for each set of holes alternate. Each hole is radiused. I would avoid rotors with a drill pattern like this:
http://neons.org/howtos/njne-kvr/show-kvr.jpg
It's more aking to perforation. Amazingly enough, I've seen a lot of porsche rotors with this type of pattern. It probably works out since porcshe tends to use rather large brakes on their cars so heat is less of an issue, but I find it pretty suspect myself.
My last car used Cross-drilled rotors sold by Stillen. They had all of these traits. It should be important to mention that it was a 240sx running on 300ZX brakes. Running large enough brakes are very important to any rotor. I would never use cross-drilling as a fix for any braking problem. Below is a photos of the rotors I used:
http://www.stillen.com/product_images/NIS3000_f.jpg
Notice there is only one hole per rotor vane and located between the vanes. The radius pattern for each set of holes alternate. Each hole is radiused. I would avoid rotors with a drill pattern like this:
http://neons.org/howtos/njne-kvr/show-kvr.jpg
It's more aking to perforation. Amazingly enough, I've seen a lot of porsche rotors with this type of pattern. It probably works out since porcshe tends to use rather large brakes on their cars so heat is less of an issue, but I find it pretty suspect myself.