I've included some highlights...
Drilled/Slotted Rotors:
Well it turns out that drilled rotors have something of a lasting problem, mostly in that they just don't. Under high stress and heat, those holes create a whole mess of weak points on the rotor, especially on cheap ones that don't drill between the cooling veins, and instead just drill a nice looking pattern whether that means going through the structurally important vein sidewalls or not. Even with good equipment from reputable brands, after repeated heating a cooling cycles, those effin sweet looking rotors start to look like this:
So why do drilled rotors exist? Funnily enough, they actually did get their start in racing way back when we still used asbestos brake pads. When these wore down at temperature, pockets of gas created by the pad would reduce brake effectiveness during a race. This was called out-gassing, and our modern semi-metallic or ceramic pads do not have this same problem. So now these holes are put there under the guise of cooling more effectively, which is partially true, because drilled rotors do tend to run cooler. Where there is debate, though, is how much of this effectiveness comes from the (not insignificant) lack of surface area to create that heat, and how much is due to good airflow. Either way, there are better ways to cool your rotors that don't involve ruining their structural integrity.
All metals flex and "grow" when heated up, the cast iron rotors on your car are no different. When a piece of metal is repeatedly heated and cooled, it relies on the entire structure to flex evenly along with it. Introducing big, evenly spaced holes just gives the metal more wiggle room to flex on its own as its temperature changes unevenly to the metal around it. Drilling holes means less surface tension to combat this issue. There is no perfect way to heat and cool our rotors completely evenly while driving, so this is just a fact of life. This is why you will never see any serious modern race car running drilled rotors. Go ahead, Google it. I know I did when I first read about this.
So what about slotted rotors? Well a few racing organizations actually do use slotted rotors, Nascar and many LeMans cars included. The idea is that the slots give the dust from between the rotor and the pad a place to go (even though most front pads have this built in), as well as "wiping" your pads to mitigate glazing (more on that later). The problem here is that if you have glazed your pads, you have already heated them up past their intended heat range, and the pad has literally melted against the rotor's surface. To say that these slots will resurface your pads for you is both optimistic and ignoring the fact that you pushed your equipment passed what it was designed to handle.
I should mention that one legitimate benefit of drilled and slotted rotors (besides attracting the hunnies, y'all), is in wet weather conditions. The gaps give the water a channel to run out, much like the tread on your tires for better wet weather braking. Also, none of this is to say that blank rotors don't crack. They do, just not nearly as often and under more extreme conditions.
So why do drilled rotors exist? Funnily enough, they actually did get their start in racing way back when we still used asbestos brake pads. When these wore down at temperature, pockets of gas created by the pad would reduce brake effectiveness during a race. This was called out-gassing, and our modern semi-metallic or ceramic pads do not have this same problem. So now these holes are put there under the guise of cooling more effectively, which is partially true, because drilled rotors do tend to run cooler. Where there is debate, though, is how much of this effectiveness comes from the (not insignificant) lack of surface area to create that heat, and how much is due to good airflow. Either way, there are better ways to cool your rotors that don't involve ruining their structural integrity.
All metals flex and "grow" when heated up, the cast iron rotors on your car are no different. When a piece of metal is repeatedly heated and cooled, it relies on the entire structure to flex evenly along with it. Introducing big, evenly spaced holes just gives the metal more wiggle room to flex on its own as its temperature changes unevenly to the metal around it. Drilling holes means less surface tension to combat this issue. There is no perfect way to heat and cool our rotors completely evenly while driving, so this is just a fact of life. This is why you will never see any serious modern race car running drilled rotors. Go ahead, Google it. I know I did when I first read about this.
So what about slotted rotors? Well a few racing organizations actually do use slotted rotors, Nascar and many LeMans cars included. The idea is that the slots give the dust from between the rotor and the pad a place to go (even though most front pads have this built in), as well as "wiping" your pads to mitigate glazing (more on that later). The problem here is that if you have glazed your pads, you have already heated them up past their intended heat range, and the pad has literally melted against the rotor's surface. To say that these slots will resurface your pads for you is both optimistic and ignoring the fact that you pushed your equipment passed what it was designed to handle.
I should mention that one legitimate benefit of drilled and slotted rotors (besides attracting the hunnies, y'all), is in wet weather conditions. The gaps give the water a channel to run out, much like the tread on your tires for better wet weather braking. Also, none of this is to say that blank rotors don't crack. They do, just not nearly as often and under more extreme conditions.
Nope. They're not warped and they never were warped. You know what? You're warped. (Yeah, go ahead and tell mom, I don't even care!)
I'll admit, part of the reason why I started doing all this research in the beginning was because I was pretty sure my brakes were warped and I wanted to get new rotors. At first I found all the typical tips and info, but because I'm a loser who researches the absolute shit out of everything, I stumbled upon some people calling bullshit on the whole warped rotor idea. Seriously, I had to look all the way down to like, the bottom 3/4ths of a Google search page to find this stuff. That's how deep I go for you guys. Anyway, getting to the point...
Here's a quote from professional racer, Carroll Smith:
"...in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc."
This is from an extremely interesting write up that he did for StopTech years ago, and if you want to get really in depth with this stuff, I suggest you check it out along with some of the other technical papers they have published on their site, some going deep into the physics and chemistry of it all — and by deep, I mean half the stuff flew about 7.5 feet right over my head. I'll give you a more simplified version of what's going on when your rotors feel and have been measured to be warped. Pay attention, there will be a quiz later.
First, we need to establish how your brakes work.
When applying the brakes on your car, the caliper squeezes two brake pads to the spinning rotor, creating friction against the rotating mass of your tires and slowing you down. There are two types of friction at play here, abrasive friction and adherent fiction. Abrasive friction literally breaks the bonds of the crystalline structure of the pad and even the cast iron of the disc, creating heat. Mohs Law tells us that the harder material (ideally the disc) wears away at the softer material of the pad as the two materials rub together. Picture a sanding pad against a board. Same concept.
Adherent friction is where some of the pad material literally adheres to the opposing surface as they scrape by each other, creating a thin and (ideally) even layer of pad material on the face of the rotor. That material can continually break its bonds and transfer from surface to surface back and forth between the disc and the pad, continually breaking and reforming like they were bouncing across political parties between elections (heyoo!).
Good performing pads need to strike a balance between these two types of friction. A primarily abrasive pad will have a quick wear rate and will fade at high temperatures as it's structure weakens and gives, no longer stiff enough to be abrasive. A primarily adherent pad will result in too much build up, as it is not abrasive enough to scrape the disc clean and uniform, and requires much higher temperatures to be effective. Between these two is where the balance needs to strike for good street pads — something that can handle being ridden all the way down a long hill without fading to nothing once you reach the bottom, and something that can still stop your car effectively on a cold morning. This is why a racing pad that requires high heat to work effectively and can be so dangerous on the street.
So how do my brakes "warp" then?
So going back to that adhesive friction stuff, if a pad is not properly broken in (yes, this is a thing), the material that transfers between the pad and the disc can do so in a seemingly random, uneven fashion creating islands of deposits that keep growing, leaving high and low spots on the disc. Another problem is if you hold the pad against the rotor after intense braking or coming down from a high speed, the pad can literally leave a print of material on the disc like the image from StopTech above shows.
The other way your rotors can feel warped happens when your discs develop heat spots. Modern cast iron rotors are an alloy of iron and silicon mixed with particles of carbon. At high temperatures, spots of silicon carbides form and create uneven hot spots, growing in temperature faster than the iron around it. Once this temperature reaches up around 1300 degrees Fahrenheit, the cast iron around that area begins to form cementite, or iron carbide which is very dense, abrasive, susceptible to cracks, and conducts much more heat than the cast iron around it. Once the cementite forms, continued use will just heat up those spots, causing them to heat the iron around them and form even more cementite. It's a vicious cycle.
Resurfacing your rotors can remove the cementite if you catch it early enough, but it's very unlikely and most times you'll be back in the shop after a few months getting them replaced all together. It's a band aid fix for a larger issue, and honestly isn't even really all that cost effective over a set of decent replacement rotors and the knowledge of how to keep this from happening again.
I'll admit, part of the reason why I started doing all this research in the beginning was because I was pretty sure my brakes were warped and I wanted to get new rotors. At first I found all the typical tips and info, but because I'm a loser who researches the absolute shit out of everything, I stumbled upon some people calling bullshit on the whole warped rotor idea. Seriously, I had to look all the way down to like, the bottom 3/4ths of a Google search page to find this stuff. That's how deep I go for you guys. Anyway, getting to the point...
Here's a quote from professional racer, Carroll Smith:
"...in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc."
This is from an extremely interesting write up that he did for StopTech years ago, and if you want to get really in depth with this stuff, I suggest you check it out along with some of the other technical papers they have published on their site, some going deep into the physics and chemistry of it all — and by deep, I mean half the stuff flew about 7.5 feet right over my head. I'll give you a more simplified version of what's going on when your rotors feel and have been measured to be warped. Pay attention, there will be a quiz later.
First, we need to establish how your brakes work.
When applying the brakes on your car, the caliper squeezes two brake pads to the spinning rotor, creating friction against the rotating mass of your tires and slowing you down. There are two types of friction at play here, abrasive friction and adherent fiction. Abrasive friction literally breaks the bonds of the crystalline structure of the pad and even the cast iron of the disc, creating heat. Mohs Law tells us that the harder material (ideally the disc) wears away at the softer material of the pad as the two materials rub together. Picture a sanding pad against a board. Same concept.
Adherent friction is where some of the pad material literally adheres to the opposing surface as they scrape by each other, creating a thin and (ideally) even layer of pad material on the face of the rotor. That material can continually break its bonds and transfer from surface to surface back and forth between the disc and the pad, continually breaking and reforming like they were bouncing across political parties between elections (heyoo!).
Good performing pads need to strike a balance between these two types of friction. A primarily abrasive pad will have a quick wear rate and will fade at high temperatures as it's structure weakens and gives, no longer stiff enough to be abrasive. A primarily adherent pad will result in too much build up, as it is not abrasive enough to scrape the disc clean and uniform, and requires much higher temperatures to be effective. Between these two is where the balance needs to strike for good street pads — something that can handle being ridden all the way down a long hill without fading to nothing once you reach the bottom, and something that can still stop your car effectively on a cold morning. This is why a racing pad that requires high heat to work effectively and can be so dangerous on the street.
So how do my brakes "warp" then?
So going back to that adhesive friction stuff, if a pad is not properly broken in (yes, this is a thing), the material that transfers between the pad and the disc can do so in a seemingly random, uneven fashion creating islands of deposits that keep growing, leaving high and low spots on the disc. Another problem is if you hold the pad against the rotor after intense braking or coming down from a high speed, the pad can literally leave a print of material on the disc like the image from StopTech above shows.
The other way your rotors can feel warped happens when your discs develop heat spots. Modern cast iron rotors are an alloy of iron and silicon mixed with particles of carbon. At high temperatures, spots of silicon carbides form and create uneven hot spots, growing in temperature faster than the iron around it. Once this temperature reaches up around 1300 degrees Fahrenheit, the cast iron around that area begins to form cementite, or iron carbide which is very dense, abrasive, susceptible to cracks, and conducts much more heat than the cast iron around it. Once the cementite forms, continued use will just heat up those spots, causing them to heat the iron around them and form even more cementite. It's a vicious cycle.
Resurfacing your rotors can remove the cementite if you catch it early enough, but it's very unlikely and most times you'll be back in the shop after a few months getting them replaced all together. It's a band aid fix for a larger issue, and honestly isn't even really all that cost effective over a set of decent replacement rotors and the knowledge of how to keep this from happening again.
Anyway this info is pretty much what I've been telling people for a while. Rotors DO NOT warp. Slots and Drilled rotors do not provide any meaningful benefit. Big brakes do not shorten stopping distances. Crazy track pads do not shorten stopping distances.
Discuss....
Reply With Quote
Originally Posted by a4darkness
Bookmarks