Suposedly the truth about Brakes, what do you think ?
12-20-2007, 12:57 PM
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Burning Brakes
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Suposedly the truth about Brakes, what do you think ?
The Truth About Brakes, What Do You Think ?
I didn't write this but found it interesting. I'm curious if there are other thoughts from the Corvette guy's. -Garry
The Working of Brakes
Over the past several years I have seen many myths perpetrated by the main stream. The purpose of this article is to dispel some of those myths while explaining basic concepts. Through the course of this article you will learn about how brakes work. You will also learn the advantages and disadvantages of cross-drilled, slotted, and vented rotors. Lastly, you will learn about brake bias.
There is a common fallacy out there that increasing your brake pad size in terms of swept area will increase the stopping power of your car through greater friction. From a standpoint ignoring operating temperatures this is in fact false. The force of friction is determined by physics as the force down on the object times the coefficient of friction. As such there is no surface area in the friction equation. However, the temperature of the pad varies throughout its use changing the coefficient of friction at each point along its temperature slope in a non-linear/non-progressive manner. As such it is possible that a larger pad will change the friction force favorably given pad makeup. It certainly will change the amount of time before the brakes enter the proper range and when they leave the range. It will also influence when and how long it is at the peak performance point. Meanwhile, modifying the pad material can change this operating range. As such the affect of increase in pad size on braking friction would depend on the makeup of the pad. Also note that the only way to modify the force down is to change the brake piston force (by size changes or number for example).
This does not mean that a larger brake pad does not help braking! The benefit of a large brake pad comes into effect when you consider thermal dissipation. The larger the pad the more this thermal temperature (created by the interaction between the pad and rotor) is spread amongst a pad. This means less temperature is concentrated at one point on the pad and the rotor absorbs more heat. This decreases the likelihood that the pad itself will heat beyond operating temperature. If the pad were to go beyond operating temperature it would glaze over resulting in brake fade. Furthermore, a larger pad results in a longer service life of the pad since there is more pad material to consume.
**Note: This is not to say that a huge pad is the way to go. I am simply telling you the benefits of a bigger pad. Do not. I repeat do not buy a huge pad thinking that will be the end all. However, consider a pad with a better material makeup for a large difference.
Cross-Drilled /Slotted Rotors
The second thing you can do to improve your brake performance is often to go to a larger rotor. We all know that this gives the rotor further ability to dissipate heat away from the pads through itself and through the air (conductive and convective heat transfer). So obviously a larger pad, a larger rotor, or both result in better brake performance by avoiding brake fade.
But what about cross drilled or slotted rotors? Well the common belief in the main stream is that somehow slotted or cross-drilled rotors allow for better performance by handling heat. This is 100 percent false. The individuals involved in such fallacies mention that air through the holes or slots work to cool the rotor (convective heat transfer into the air from the rotor). The issue is that from physics we know that metal transfers heat better then air by a significant amount. As such the larger mass of the rotor becomes more important then the larger surface area of the rotor in any situation other then the optimal. Cross drilling and slotting rotors are not optimal manners of creating metal to air transfer through larger surface areas. There is not much airflow through the holes or slots. Furthermore for cross drilling the holes will fill with brake dust in effect lowering the cooling ability of the rotors vanes they pass through.
Rigidity
From the information above we can glean that the rotor begins to work as a heat sink. Now by cross drilling or slotting we are decreasing the overall amount of metal to transfer this heat to. Clearly we are decreasing performance of the rotor to dissipate heat amongst itself. Furthermore, the holes of a cross-drilled or slotted rotor decrease the area of the pad that contacts the rotor. This concentrates the heat more on certain areas of the pad, which has similar effects to that of using a smaller pad. As such the pad heats up more quickly.
We are also damaging the brakes structural rigidity. The iron in a brake rotor is made of a crystalline structure. By drilling holes in said surface we cut the end grains creating a situation that breeds cracks. Furthermore, even if we were to cut the rotors correctly to avoid cutting the end grains structural rigidity is still decreased. The temperature around the holes will be slightly less then that of the entire rotor leading to temperature stress. Moreover, the decreased mass will result in lowered rigidity.
Advantages
So what do cross drilled and slotted rotors accomplish? The main original purpose of slotted and cross-drilled rotors was to vent gases that buildup between the pads and the rotors. However, this reasoning is no longer valid. As the years have gone by pads have been designed that produce very little gas. Furthermore many pads come with groves in themselves that allow for the removal of any minor gas that is created. A slotted or drilled rotor always decreases the rotors capability to dissipate heat amongst itself. A slotted or drilled rotor will also clean off the brake pad as it passes the slots at the expense of faster pad wear. As such there are benefits for rally and dirt tracks. Furthermore, the slots or holes themselves can serve to wipe off the top layer of glaze that tends to appear on your brake pads. Some racers say this last part is beneficial while others question whether the slots will fill before the deglaze affect is ever helpful. I have yet to determine the answer to this question.
The answer of slotted and cross-drilled rotor usefulness seems to lie with whether the benefit of cleaning the pads outstrips the loss in heat dissipation. In terms of cross drilling there are so many costs that nothing is accomplished beyond perhaps giving you a certain bling look. In a motorcycle or other extremely light vehicle the decrease in rotational inertia and unsprung mass might perhaps be useful (once other more efficient avenues are exhausted). However, in a street car or race car the speeds and weight of such vehicles will make the relatively miniscule decrease be outweighed by the need for more heat dissipation. Slotted rotors, meanwhile, share the positives of cross drilling but notably are slightly less subject to the costs. They do not impede airflow through the rotors vanes, nor do they have as large an affect on structural rigidity. Therefore, the need for slotting depends on your application.
Vented or Vaned
So what do ventilated rotors accomplish? Well, the concept is that they will help cool the rotors. We discussed earlier that giving up mass for surface area to gain cooling of the rotors should only be done when optimal. Vanes are the optimal method of achieving these goals. The rotors are designed to increase surface area and to flow air in the middle of the rotors. The increased surface area to the air clearly provides for more cooling from the air at the cost of mass. So why does this method work while the others fail? The first reason is that a ventilated design flows a lot of air through a rotor. A ventilated rotor acts as a centrifugal pump sucking air into the rotors. This is why rotors with curved vanes provide better braking.
A slotted or cross-drilled design will flow very little air under heavy braking. As such the vanes of the ventilated system are far more efficient. Moreover, air moves through the center of the rotor cooling the rotor more evenly and efficiently. Furthermore, the ventilated design does not decrease the contact patch of the pad on the rotor. Finally, the design has different structural rigidity qualities then that of a cross-drilled or slotted design.
Brake Bias
So now you know that increasing your pad size and rotor size will help to stop your brake fade. You also know that swapping the pad, increasing the rotor size, or increasing the force of the pistons on the pad can increase your stopping force at the tires. Finally, you have learned to stay away from cross-drilled and look very closely at whether to use a slotted rotor.
So does that mean it is time to go get that fancy front brake kit for your car? Well, potentially no again. The first thing to consider is that in any braking setup the tires are the ultimate limiting piece. You cannot stop faster then your tires allow you to stop, ever. As such, if your car can lock it’s tires under braking consistently then better brakes will not improve your braking performance. (I stress the consistent part, as brake fade must also be combated.)
Furthermore, most people understand the idea of brake bias, but fail to understand its application. A typical car is setup with the front brakes being far more effective then the rear. Now the first thing we must realize is that from a dynamic stand point your car should have stronger front brakes. When you brake physics transfers more weight to the front axle that must be accounted for. However, in this dynamic state we also have brake bias. Your typical street car is slightly dynamically biased towards the front. This leads to the front tires locking up before the rear tires under heavy conditions. Such a situation is obviously not optimal for a car stopping quickly.
You want the stopping bias to be roughly equal given the acceleration you are traveling at (please note that the bias depends on the acceleration of the vehicle). When you have a front bias you get a more stable stop (as opposed to a rear bias where a lock can cause spins), but you also get further forward weight transfer and longer stopping distances. Most cars stock come with a minor front bias for the layman. So it is clearly discernable that by going with a bigger front brake kit you are possibly increasing your stopping distance if you do not equally modify the rear brakes, change your pads, change your tires to ones that do not lockup, or set the clamping forces lower on the front brake. Without making such changes the larger effective radius can lead to an earlier lockup of the front wheels.
I didn't write this but found it interesting. I'm curious if there are other thoughts from the Corvette guy's. -Garry
The Working of Brakes
Over the past several years I have seen many myths perpetrated by the main stream. The purpose of this article is to dispel some of those myths while explaining basic concepts. Through the course of this article you will learn about how brakes work. You will also learn the advantages and disadvantages of cross-drilled, slotted, and vented rotors. Lastly, you will learn about brake bias.
There is a common fallacy out there that increasing your brake pad size in terms of swept area will increase the stopping power of your car through greater friction. From a standpoint ignoring operating temperatures this is in fact false. The force of friction is determined by physics as the force down on the object times the coefficient of friction. As such there is no surface area in the friction equation. However, the temperature of the pad varies throughout its use changing the coefficient of friction at each point along its temperature slope in a non-linear/non-progressive manner. As such it is possible that a larger pad will change the friction force favorably given pad makeup. It certainly will change the amount of time before the brakes enter the proper range and when they leave the range. It will also influence when and how long it is at the peak performance point. Meanwhile, modifying the pad material can change this operating range. As such the affect of increase in pad size on braking friction would depend on the makeup of the pad. Also note that the only way to modify the force down is to change the brake piston force (by size changes or number for example).
This does not mean that a larger brake pad does not help braking! The benefit of a large brake pad comes into effect when you consider thermal dissipation. The larger the pad the more this thermal temperature (created by the interaction between the pad and rotor) is spread amongst a pad. This means less temperature is concentrated at one point on the pad and the rotor absorbs more heat. This decreases the likelihood that the pad itself will heat beyond operating temperature. If the pad were to go beyond operating temperature it would glaze over resulting in brake fade. Furthermore, a larger pad results in a longer service life of the pad since there is more pad material to consume.
**Note: This is not to say that a huge pad is the way to go. I am simply telling you the benefits of a bigger pad. Do not. I repeat do not buy a huge pad thinking that will be the end all. However, consider a pad with a better material makeup for a large difference.
Cross-Drilled /Slotted Rotors
The second thing you can do to improve your brake performance is often to go to a larger rotor. We all know that this gives the rotor further ability to dissipate heat away from the pads through itself and through the air (conductive and convective heat transfer). So obviously a larger pad, a larger rotor, or both result in better brake performance by avoiding brake fade.
But what about cross drilled or slotted rotors? Well the common belief in the main stream is that somehow slotted or cross-drilled rotors allow for better performance by handling heat. This is 100 percent false. The individuals involved in such fallacies mention that air through the holes or slots work to cool the rotor (convective heat transfer into the air from the rotor). The issue is that from physics we know that metal transfers heat better then air by a significant amount. As such the larger mass of the rotor becomes more important then the larger surface area of the rotor in any situation other then the optimal. Cross drilling and slotting rotors are not optimal manners of creating metal to air transfer through larger surface areas. There is not much airflow through the holes or slots. Furthermore for cross drilling the holes will fill with brake dust in effect lowering the cooling ability of the rotors vanes they pass through.
Rigidity
From the information above we can glean that the rotor begins to work as a heat sink. Now by cross drilling or slotting we are decreasing the overall amount of metal to transfer this heat to. Clearly we are decreasing performance of the rotor to dissipate heat amongst itself. Furthermore, the holes of a cross-drilled or slotted rotor decrease the area of the pad that contacts the rotor. This concentrates the heat more on certain areas of the pad, which has similar effects to that of using a smaller pad. As such the pad heats up more quickly.
We are also damaging the brakes structural rigidity. The iron in a brake rotor is made of a crystalline structure. By drilling holes in said surface we cut the end grains creating a situation that breeds cracks. Furthermore, even if we were to cut the rotors correctly to avoid cutting the end grains structural rigidity is still decreased. The temperature around the holes will be slightly less then that of the entire rotor leading to temperature stress. Moreover, the decreased mass will result in lowered rigidity.
Advantages
So what do cross drilled and slotted rotors accomplish? The main original purpose of slotted and cross-drilled rotors was to vent gases that buildup between the pads and the rotors. However, this reasoning is no longer valid. As the years have gone by pads have been designed that produce very little gas. Furthermore many pads come with groves in themselves that allow for the removal of any minor gas that is created. A slotted or drilled rotor always decreases the rotors capability to dissipate heat amongst itself. A slotted or drilled rotor will also clean off the brake pad as it passes the slots at the expense of faster pad wear. As such there are benefits for rally and dirt tracks. Furthermore, the slots or holes themselves can serve to wipe off the top layer of glaze that tends to appear on your brake pads. Some racers say this last part is beneficial while others question whether the slots will fill before the deglaze affect is ever helpful. I have yet to determine the answer to this question.
The answer of slotted and cross-drilled rotor usefulness seems to lie with whether the benefit of cleaning the pads outstrips the loss in heat dissipation. In terms of cross drilling there are so many costs that nothing is accomplished beyond perhaps giving you a certain bling look. In a motorcycle or other extremely light vehicle the decrease in rotational inertia and unsprung mass might perhaps be useful (once other more efficient avenues are exhausted). However, in a street car or race car the speeds and weight of such vehicles will make the relatively miniscule decrease be outweighed by the need for more heat dissipation. Slotted rotors, meanwhile, share the positives of cross drilling but notably are slightly less subject to the costs. They do not impede airflow through the rotors vanes, nor do they have as large an affect on structural rigidity. Therefore, the need for slotting depends on your application.
Vented or Vaned
So what do ventilated rotors accomplish? Well, the concept is that they will help cool the rotors. We discussed earlier that giving up mass for surface area to gain cooling of the rotors should only be done when optimal. Vanes are the optimal method of achieving these goals. The rotors are designed to increase surface area and to flow air in the middle of the rotors. The increased surface area to the air clearly provides for more cooling from the air at the cost of mass. So why does this method work while the others fail? The first reason is that a ventilated design flows a lot of air through a rotor. A ventilated rotor acts as a centrifugal pump sucking air into the rotors. This is why rotors with curved vanes provide better braking.
A slotted or cross-drilled design will flow very little air under heavy braking. As such the vanes of the ventilated system are far more efficient. Moreover, air moves through the center of the rotor cooling the rotor more evenly and efficiently. Furthermore, the ventilated design does not decrease the contact patch of the pad on the rotor. Finally, the design has different structural rigidity qualities then that of a cross-drilled or slotted design.
Brake Bias
So now you know that increasing your pad size and rotor size will help to stop your brake fade. You also know that swapping the pad, increasing the rotor size, or increasing the force of the pistons on the pad can increase your stopping force at the tires. Finally, you have learned to stay away from cross-drilled and look very closely at whether to use a slotted rotor.
So does that mean it is time to go get that fancy front brake kit for your car? Well, potentially no again. The first thing to consider is that in any braking setup the tires are the ultimate limiting piece. You cannot stop faster then your tires allow you to stop, ever. As such, if your car can lock it’s tires under braking consistently then better brakes will not improve your braking performance. (I stress the consistent part, as brake fade must also be combated.)
Furthermore, most people understand the idea of brake bias, but fail to understand its application. A typical car is setup with the front brakes being far more effective then the rear. Now the first thing we must realize is that from a dynamic stand point your car should have stronger front brakes. When you brake physics transfers more weight to the front axle that must be accounted for. However, in this dynamic state we also have brake bias. Your typical street car is slightly dynamically biased towards the front. This leads to the front tires locking up before the rear tires under heavy conditions. Such a situation is obviously not optimal for a car stopping quickly.
You want the stopping bias to be roughly equal given the acceleration you are traveling at (please note that the bias depends on the acceleration of the vehicle). When you have a front bias you get a more stable stop (as opposed to a rear bias where a lock can cause spins), but you also get further forward weight transfer and longer stopping distances. Most cars stock come with a minor front bias for the layman. So it is clearly discernable that by going with a bigger front brake kit you are possibly increasing your stopping distance if you do not equally modify the rear brakes, change your pads, change your tires to ones that do not lockup, or set the clamping forces lower on the front brake. Without making such changes the larger effective radius can lead to an earlier lockup of the front wheels.
Last edited by GarryL; 12-20-2007 at 12:59 PM.
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12-20-2007, 01:31 PM
#3
Drifting
Also a VERY good read from Trackbird on LS1tech.
Explanation of Cross Drilled Rotors
Separating fact from fiction
I and many of my autocrossing and road racing friends have been trying to separate the marketing hype from the product and explain the existence of Eradispeeds or any cross drilled and/or slotted brake rotors. Mostly, there seems to be a misunderstanding of the reasons for drilling holes in a perfectly good rotor. Cross drilled rotors have somehow become the "magical cure" for your brakes. Many would like you to believe that they will help you stop faster, they will wear better, stay cooler, and they can magically avoid warping. Unfortunately all of these things are false. But, since the guys who make these products spend more on advertising than I do (ok, I don't), it is easy to fall into that trap.
Broken down to the most basic physics (don't worry, no serious math involved here). You will begin to see the reasons they can't do the things they are touted to do.
The "basic" lesson:
Ok. If I am trying to boil a pot of water with 2 gallons of water in it. It will take a lot of heat to get all of that water up to boiling temperature. Right? Now, if I remove 1/2 the water and with it, 1/2 the mass used to absorb heat, it will now be easier to get that water to boil since there is less mass to absorb heat. Make sense?
Ok, If I take a 3 lb chunk of metal and a 6 lb chunk of metal and set them both over a small torch, which one do you think will heat up first? The lighter mass will see a more rapid temperature rise (it will get hotter, quicker). Correct?
Now, if I take a brake rotor that weighs 20 lbs and begin making "panic stops" with it, it's temperature will increase. Easy enough.
If I now take the same rotor, drill holes in it reducing its weight to 17 lbs and make the same "panic stops", would it not make sense (from the above examples) that the lighter rotor will end that stop with a higher temperature? Less mass to absorb heat will cause a more rapid temperature rise.
Many will say "cross drilled rotors cool better". Hmmm. If you really look at it, how much air do you think can blow through those little holes? Add the fact that they are spinning at a reasonably high speed and the cooling argument becomes even less believable. In fact, the holes could, in theory, disrupt the natural draw of air from the center of the rotor to the outside edge. That is the flow that actually cools the rotors.
Now, some of the aftermarket drilled/slotted rotors are in fact heavier than the stock parts they replace. That is good for heat absorbtion, but you still have the problem of "holes". Where there is a hole in the rotor surface, there is no friction. So, the effect is similar to reducing the size of the brake pad because less of it can touch the rotor (to make friction) at any given time.
This is from Baer racing (I don't think it is on their site any longer).
From Baer Brake Systems
What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as “green pad fade” or “outgassing”. When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting!
However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern. When shopping for races pads, or even ultra-high performance road pads, look for the phrases, “dynamic surface treatment”, “race ready”, and/or, “pre-burnished”. When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with ‘outgassing’. Ironically more pedestrian pads used on most streetcars will still exhibit ‘outgassing’, but only when used at temperatures normally only encountered on the racetrack.
Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs.
Crossdrilling offers the greatest gas relief pathway, but creates potential “stress risers” from which cracks can occur. Baer’s rotors are cast with crossdrilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings.
From Brembo:
From Brembo
Why use drilled or slotted discs?
Drilling or slotting discs aids the disc in several ways:
The edges of the slots or holes continuously clean and refresh the pad surface as well as providing increased brake "bite". Additionally, they prevent gasses from collecting between the pad and disc interface.
The disc is lightened, thereby decreasing its rotational inertia.
Improved ventilation increases the disc's ability to shed heat, resulting in cooler operating temperatures.
Wilwood:
From Wilwood
Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.
And Stoptech:
Discs that have been drilled through with a non-intersecting pattern of radial holes. The objects are to provide a number of paths to get rid of the boundary layer of out gassed volatiles and incandescent particles of friction material and to increase "bite" through the provision of many leading edges. The advent of carbon metallic friction materials with their increased temperatures and thermal shock characteristics ended the day of the drilled disc in professional racing. They are still seen (mainly as cosmetic items) on motorbikes and some road going sports cars. Typically in original equipment road car applications these holes are cast then finished machined to provide the best possible conditions by which to resist cracking in use. But they will crack eventually under the circumstances described in another section (see Cracking). Properly designed, drilled discs tend to operate cooler than non-drilled ventilated discs of the same design due the higher flow rates through the vents from the supplemental inlets and increased surface area in the hole. That's right, inlets. The flow is into the hole and out through the vent to the OD of the disc. If discs are to be drilled, the external edges of the holes must be chamfered (or, better yet, radiused) and should also be peened.
The reason:
Rotors were originally drilled to eliminate something known as "green fade". The best way to explain "Green fade" is to relate it to an air hockey table. The puck is suspended on a cushion of air that prevents it from touching the table, this reduces the friction between the puck and the table.
A long time ago, pads were made with the best resins we had available. Many of those resins would produce gas as they cured. When a pad was used the first few times, the heat would "cure" the resin which would cause it to produce vapors. This was known as "out gassing". The vapors would build up between the pad and the rotor and lift or "force" the pad away from the rotor (like the puck in air hockey). This caused the brakes to be very ineffective, even though they were not yet at the maximum rated operating temperature. The holes were drilled to allow that gas a place to escape. So, it is correct to say that rotors were cross drilled to eliminate fade, but not for the reasons you would think. The good news is that today's resins no longer suffer from these problem and the modern race pads are so good that this is really no longer an issue. So, by cross drilling rotors, you will only manage to shorten the lifespan of that rotor (it now has less surface area to wear against the brake pad and will wear more quickly as well as a reduction in weight that will cause the brakes to operate at a higher temperature).
Another problem with cross drilled rotors is the potential for cracking around the holes. The holes become a stress point in the cast iron that can more readily allow cracks to form in the rotor surface. This requires that you pay close attention to the rotor surface for signs of cracking. Some small cracks, known as "surface checking" are acceptable, but anything that resembles a crack would be a reason to replace that rotor. When looking at slotted rotors keep in mind that the slots should not be milled off of the edge of the rotor. This is a great place for cracks to form, and they will. The slot should be ball milled in the rotor face and originate and terminate on the surface of the rotor without exiting the rotors edge. The goal is to eliminate sharp edges that cause stress risers on the rotor surface. This will reduce the possibility of cracking. If you see slotted rotors with slots that are milled off the edge of the rotor, shop for another brand. Slots that are not cut through the edge of the rotor are a good sign that the manufacturer of that rotor knows what they are doing. This is a good indicator of parts made by a brake company and not a machine shop that happens to drill and slot rotors.
Many years ago, when I ordered my first brake kit from Baer Racing, they told me that drilled rotors would typically last 20% less than an equivalent solid rotor. This was why they always recommended solid rotors for extreme use. Baer has changed their stance on this since discovering there was a large amount of money to be made selling "Eradispeeds" (they are very pretty brake rotors). This change in their marketing strategy has caused me to feel that they have gone from "supporting the racing community" to "making maximum money". And, I guess I can't blame them.....
If you are truly looking for upgraded braking performance for your car. I suggest, as a first upgrade, that you leave the stock size rotors and upgrade the pads. Try a set of Hawk HPS pads or something from Larry at Carbotech Engineering (www.carbotecheng.com) <http://www.carbotecheng.com)>. You'll think you put "big brakes" on all 4 corners (compared to stock).
If you must go bigger, look at any of the various brake upgrades available from many major manufacturers. Brembo, Baer, and many others will have what you need, if you need to upgrade. There are larger kits and they increase in both cost and braking ability. Only your needs and your budget are the limit.
Tires:
I'd also like to take a moment to address the impact that tires have on braking performance.
While it is true that the tires have the "last word" with the pavement when it comes to how the car accelerates, turns, and brakes. There are a few things that tires can and can't do. While it is true that a car on wide, sticky tires should and will out brake the same car on thin, non-grippy tires (all other things being equal). And, while tires are extremely important. They become less important on the 5th or 8th stop or the 3rd lap of a road course. By then the brakes (depending on rotor size, cooling, pads, etc) may be so hot that they can't lock up the skinny little tires, much less the wide, grippy ones. This is where upgrading the brakes pays dividends. This is not meant to minimize the tires role in braking performance. Simply, you must remember to weigh the tires limits against the brake systems limits. You are working with a "package" and changes in one can impact the other. So, while tires will be the limit on the first few stops, they will play a less important role as the brake system temperatures increase. Remember, just because you can lock up the tires on the first stop does not mean that you can't benefit from brake system upgrades.
Class dismissed.
Have fun!
The abbreviated version:
For those who want the short version.
Eradispeeds will not slow your car down any better than stock rotors. They are built to look pretty in the driveway. Iron has a very similar coefficient of friction and it is all about the same. A rotor only has so much metal in it. Metal absorbs heat, metal with holes in it, is lighter than metal without, this makes it lighter, this will allow it to absorb less heat. So, you will not see any miracles from a set of Eradispeeds. Catchy name, shiny parts, great marketing, but they are still "just rotors". Pads...the pads will make a difference (and for much less money). Rotors are still a wear item, and for the money they are asking, I'd hate to run aggressive pads that chew up rotors on slotted, drilled or Eradispeed rotors. However, those same upgraded pads will stop your car and very well. So, I'd buy $60 rotors and $100 pads, instead of $20 pads and $800 rotors. You'll be happier with the result.
Be safe!
Separating fact from fiction
I and many of my autocrossing and road racing friends have been trying to separate the marketing hype from the product and explain the existence of Eradispeeds or any cross drilled and/or slotted brake rotors. Mostly, there seems to be a misunderstanding of the reasons for drilling holes in a perfectly good rotor. Cross drilled rotors have somehow become the "magical cure" for your brakes. Many would like you to believe that they will help you stop faster, they will wear better, stay cooler, and they can magically avoid warping. Unfortunately all of these things are false. But, since the guys who make these products spend more on advertising than I do (ok, I don't), it is easy to fall into that trap.
Broken down to the most basic physics (don't worry, no serious math involved here). You will begin to see the reasons they can't do the things they are touted to do.
The "basic" lesson:
Ok. If I am trying to boil a pot of water with 2 gallons of water in it. It will take a lot of heat to get all of that water up to boiling temperature. Right? Now, if I remove 1/2 the water and with it, 1/2 the mass used to absorb heat, it will now be easier to get that water to boil since there is less mass to absorb heat. Make sense?
Ok, If I take a 3 lb chunk of metal and a 6 lb chunk of metal and set them both over a small torch, which one do you think will heat up first? The lighter mass will see a more rapid temperature rise (it will get hotter, quicker). Correct?
Now, if I take a brake rotor that weighs 20 lbs and begin making "panic stops" with it, it's temperature will increase. Easy enough.
If I now take the same rotor, drill holes in it reducing its weight to 17 lbs and make the same "panic stops", would it not make sense (from the above examples) that the lighter rotor will end that stop with a higher temperature? Less mass to absorb heat will cause a more rapid temperature rise.
Many will say "cross drilled rotors cool better". Hmmm. If you really look at it, how much air do you think can blow through those little holes? Add the fact that they are spinning at a reasonably high speed and the cooling argument becomes even less believable. In fact, the holes could, in theory, disrupt the natural draw of air from the center of the rotor to the outside edge. That is the flow that actually cools the rotors.
Now, some of the aftermarket drilled/slotted rotors are in fact heavier than the stock parts they replace. That is good for heat absorbtion, but you still have the problem of "holes". Where there is a hole in the rotor surface, there is no friction. So, the effect is similar to reducing the size of the brake pad because less of it can touch the rotor (to make friction) at any given time.
This is from Baer racing (I don't think it is on their site any longer).
From Baer Brake Systems
What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as “green pad fade” or “outgassing”. When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting!
However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern. When shopping for races pads, or even ultra-high performance road pads, look for the phrases, “dynamic surface treatment”, “race ready”, and/or, “pre-burnished”. When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with ‘outgassing’. Ironically more pedestrian pads used on most streetcars will still exhibit ‘outgassing’, but only when used at temperatures normally only encountered on the racetrack.
Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs.
Crossdrilling offers the greatest gas relief pathway, but creates potential “stress risers” from which cracks can occur. Baer’s rotors are cast with crossdrilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings.
From Brembo:
From Brembo
Why use drilled or slotted discs?
Drilling or slotting discs aids the disc in several ways:
The edges of the slots or holes continuously clean and refresh the pad surface as well as providing increased brake "bite". Additionally, they prevent gasses from collecting between the pad and disc interface.
The disc is lightened, thereby decreasing its rotational inertia.
Improved ventilation increases the disc's ability to shed heat, resulting in cooler operating temperatures.
Wilwood:
From Wilwood
Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.
And Stoptech:
Discs that have been drilled through with a non-intersecting pattern of radial holes. The objects are to provide a number of paths to get rid of the boundary layer of out gassed volatiles and incandescent particles of friction material and to increase "bite" through the provision of many leading edges. The advent of carbon metallic friction materials with their increased temperatures and thermal shock characteristics ended the day of the drilled disc in professional racing. They are still seen (mainly as cosmetic items) on motorbikes and some road going sports cars. Typically in original equipment road car applications these holes are cast then finished machined to provide the best possible conditions by which to resist cracking in use. But they will crack eventually under the circumstances described in another section (see Cracking). Properly designed, drilled discs tend to operate cooler than non-drilled ventilated discs of the same design due the higher flow rates through the vents from the supplemental inlets and increased surface area in the hole. That's right, inlets. The flow is into the hole and out through the vent to the OD of the disc. If discs are to be drilled, the external edges of the holes must be chamfered (or, better yet, radiused) and should also be peened.
The reason:
Rotors were originally drilled to eliminate something known as "green fade". The best way to explain "Green fade" is to relate it to an air hockey table. The puck is suspended on a cushion of air that prevents it from touching the table, this reduces the friction between the puck and the table.
A long time ago, pads were made with the best resins we had available. Many of those resins would produce gas as they cured. When a pad was used the first few times, the heat would "cure" the resin which would cause it to produce vapors. This was known as "out gassing". The vapors would build up between the pad and the rotor and lift or "force" the pad away from the rotor (like the puck in air hockey). This caused the brakes to be very ineffective, even though they were not yet at the maximum rated operating temperature. The holes were drilled to allow that gas a place to escape. So, it is correct to say that rotors were cross drilled to eliminate fade, but not for the reasons you would think. The good news is that today's resins no longer suffer from these problem and the modern race pads are so good that this is really no longer an issue. So, by cross drilling rotors, you will only manage to shorten the lifespan of that rotor (it now has less surface area to wear against the brake pad and will wear more quickly as well as a reduction in weight that will cause the brakes to operate at a higher temperature).
Another problem with cross drilled rotors is the potential for cracking around the holes. The holes become a stress point in the cast iron that can more readily allow cracks to form in the rotor surface. This requires that you pay close attention to the rotor surface for signs of cracking. Some small cracks, known as "surface checking" are acceptable, but anything that resembles a crack would be a reason to replace that rotor. When looking at slotted rotors keep in mind that the slots should not be milled off of the edge of the rotor. This is a great place for cracks to form, and they will. The slot should be ball milled in the rotor face and originate and terminate on the surface of the rotor without exiting the rotors edge. The goal is to eliminate sharp edges that cause stress risers on the rotor surface. This will reduce the possibility of cracking. If you see slotted rotors with slots that are milled off the edge of the rotor, shop for another brand. Slots that are not cut through the edge of the rotor are a good sign that the manufacturer of that rotor knows what they are doing. This is a good indicator of parts made by a brake company and not a machine shop that happens to drill and slot rotors.
Many years ago, when I ordered my first brake kit from Baer Racing, they told me that drilled rotors would typically last 20% less than an equivalent solid rotor. This was why they always recommended solid rotors for extreme use. Baer has changed their stance on this since discovering there was a large amount of money to be made selling "Eradispeeds" (they are very pretty brake rotors). This change in their marketing strategy has caused me to feel that they have gone from "supporting the racing community" to "making maximum money". And, I guess I can't blame them.....
If you are truly looking for upgraded braking performance for your car. I suggest, as a first upgrade, that you leave the stock size rotors and upgrade the pads. Try a set of Hawk HPS pads or something from Larry at Carbotech Engineering (www.carbotecheng.com) <http://www.carbotecheng.com)>. You'll think you put "big brakes" on all 4 corners (compared to stock).
If you must go bigger, look at any of the various brake upgrades available from many major manufacturers. Brembo, Baer, and many others will have what you need, if you need to upgrade. There are larger kits and they increase in both cost and braking ability. Only your needs and your budget are the limit.
Tires:
I'd also like to take a moment to address the impact that tires have on braking performance.
While it is true that the tires have the "last word" with the pavement when it comes to how the car accelerates, turns, and brakes. There are a few things that tires can and can't do. While it is true that a car on wide, sticky tires should and will out brake the same car on thin, non-grippy tires (all other things being equal). And, while tires are extremely important. They become less important on the 5th or 8th stop or the 3rd lap of a road course. By then the brakes (depending on rotor size, cooling, pads, etc) may be so hot that they can't lock up the skinny little tires, much less the wide, grippy ones. This is where upgrading the brakes pays dividends. This is not meant to minimize the tires role in braking performance. Simply, you must remember to weigh the tires limits against the brake systems limits. You are working with a "package" and changes in one can impact the other. So, while tires will be the limit on the first few stops, they will play a less important role as the brake system temperatures increase. Remember, just because you can lock up the tires on the first stop does not mean that you can't benefit from brake system upgrades.
Class dismissed.
Have fun!
The abbreviated version:
For those who want the short version.
Eradispeeds will not slow your car down any better than stock rotors. They are built to look pretty in the driveway. Iron has a very similar coefficient of friction and it is all about the same. A rotor only has so much metal in it. Metal absorbs heat, metal with holes in it, is lighter than metal without, this makes it lighter, this will allow it to absorb less heat. So, you will not see any miracles from a set of Eradispeeds. Catchy name, shiny parts, great marketing, but they are still "just rotors". Pads...the pads will make a difference (and for much less money). Rotors are still a wear item, and for the money they are asking, I'd hate to run aggressive pads that chew up rotors on slotted, drilled or Eradispeed rotors. However, those same upgraded pads will stop your car and very well. So, I'd buy $60 rotors and $100 pads, instead of $20 pads and $800 rotors. You'll be happier with the result.
Be safe!
12-21-2007, 01:16 AM
#6
Le Mans Master
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St. Jude Donor '13-'14-'15
Very true--Ever see a Nascar short-track rotor/pad assembly up close ?
I worked on a winston west crew for years and you will never see drilled or slotted rotors and the rotors are about 1 3/4" thick and the pads are 1" thick per side--More rotor metal--more pad material = better heat disapation
12-21-2007, 10:15 AM
#7
Safety Car
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St. Jude Donor '08
^^ I would largely agree with the article from everything I have read. Carroll Smith talks a lot about brakes in his book "Tuning to Win". Pretty interesting read.
I too am sticking with stock brake set-up, except for going to better pads. But I have larger than stock tires on my car and the rubber compound is stickier, which should greatly increase traction.
I too am sticking with stock brake set-up, except for going to better pads. But I have larger than stock tires on my car and the rubber compound is stickier, which should greatly increase traction.
12-21-2007, 10:24 AM
#8
Team Owner
Sounds spot on!
It makes sense! I do like my drilled and slotted Wildwood brakes and they work perfect with my high friction pads!
Thanks,Matt
It makes sense! I do like my drilled and slotted Wildwood brakes and they work perfect with my high friction pads!
Thanks,Matt
12-21-2007, 10:58 AM
#9
Tech Contributor
Interesting. While surface area is not included in the equation for calculating kinetic friction force, is does have a tremendous effect on braking. It is all about the force applied about a surface area, not the surface area itself. Try reducing your brake pads to a suface area of 2" x 2 ", and see how well your brakes stop the car.
For example: Have you ever seen that commercial for a vacuum cleaner where they pick up a bowling ball to demonstrate how powerful the vacuum is? They use a large cup that covers a large surface area of the bowling ball. Even a small amount of vacuum applied to that surface area will pick up the bowling ball. If they reduced the size of the cup, thus reducing the affected surface are on the bowling ball, the vacuum cleaner could not pick it up.
For example: Have you ever seen that commercial for a vacuum cleaner where they pick up a bowling ball to demonstrate how powerful the vacuum is? They use a large cup that covers a large surface area of the bowling ball. Even a small amount of vacuum applied to that surface area will pick up the bowling ball. If they reduced the size of the cup, thus reducing the affected surface are on the bowling ball, the vacuum cleaner could not pick it up.
Last edited by lucky131969; 12-22-2007 at 10:02 AM.
12-21-2007, 06:57 PM
#10
Le Mans Master
Origional Post was spot on.
The ONLY reason I'm not still running OEM calipers is because I had to replace them anyways and the LG/Wilwood kit lets me use OEM rotors with a much thicker pad (that happens to be cheaper than OEM pads), so the long term cost is cheaper. The added bonus is that the calipers make it much easier to swap out pads/rotors so I save time there too.
The ONLY reason I'm not still running OEM calipers is because I had to replace them anyways and the LG/Wilwood kit lets me use OEM rotors with a much thicker pad (that happens to be cheaper than OEM pads), so the long term cost is cheaper. The added bonus is that the calipers make it much easier to swap out pads/rotors so I save time there too.
12-21-2007, 07:08 PM
#11
Le Mans Master
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Origional Post was spot on.
The ONLY reason I'm not still running OEM calipers is because I had to replace them anyways and the LG/Wilwood kit lets me use OEM rotors with a much thicker pad (that happens to be cheaper than OEM pads), so the long term cost is cheaper. The added bonus is that the calipers make it much easier to swap out pads/rotors so I save time there too.
The ONLY reason I'm not still running OEM calipers is because I had to replace them anyways and the LG/Wilwood kit lets me use OEM rotors with a much thicker pad (that happens to be cheaper than OEM pads), so the long term cost is cheaper. The added bonus is that the calipers make it much easier to swap out pads/rotors so I save time there too.
12-22-2007, 12:17 AM
#12
Race Director
A couple of things were missing from the above-listed info.
1. No mention was made of uneven pad deposits - a very real and irritating problem with stock rotors and pads - and not just C5 rotors and pads. Many types of vehicles have the same problem with pulsating brakes. Slotted rotors do prevent or eliminate this malady.
2. Wet conditions: Slots help get rid of water, just as grooves in tires help channel water away from the tire/road interface.
And anyone who things glazing is a thing of the past doesn't have a vehicle that isn't driven much. Chances are if you don't change pads every 8 years or so (and you have blank rotors), your braking effectiveness is diminished. Slotted rotors take care of this very nicely.
1. No mention was made of uneven pad deposits - a very real and irritating problem with stock rotors and pads - and not just C5 rotors and pads. Many types of vehicles have the same problem with pulsating brakes. Slotted rotors do prevent or eliminate this malady.
2. Wet conditions: Slots help get rid of water, just as grooves in tires help channel water away from the tire/road interface.
And anyone who things glazing is a thing of the past doesn't have a vehicle that isn't driven much. Chances are if you don't change pads every 8 years or so (and you have blank rotors), your braking effectiveness is diminished. Slotted rotors take care of this very nicely.
12-22-2007, 01:21 AM
#14
Race Director
Let's put it this way....
With OEM rotors and pads, my brake pedal was pulsing badly at 6000 miles. The dealership turned the rotors and after another 6000 miles, the brake peday was again doing the pulsation dance.
After installing PowerSlots and 20,000 miles later, NO pulsations whatsoever.
Are slotted rotors bling only - I think not!
With OEM rotors and pads, my brake pedal was pulsing badly at 6000 miles. The dealership turned the rotors and after another 6000 miles, the brake peday was again doing the pulsation dance.
After installing PowerSlots and 20,000 miles later, NO pulsations whatsoever.
Are slotted rotors bling only - I think not!
12-22-2007, 07:58 AM
#15
Team Owner
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Remember guys braking has a lot to do with the your front tires. Wider and sticker ( softer rubber) means better stopping.
With almost 4 years of track days under my frame, I use stock calipers, Stock / Raybestos rotors, Castrol SRF brake fluid and PFC-01s and now Wilwood H brake pads. ( parts are replaced as needed)
Plus being an instructor I have driven countless number of Porches, BMWs and other cars on the track. Many have had BBKs of all different makes.
I have even driven a few Porsches 996 RSs ( race prepared). IMO our stock brakes work far better then many BBKs. Then when adding wide sticky front tires, our brakes work far better. Does our equipment last as long? No. Do our brakes look as Cool as a BBK? No
The Corvette 2 pot PBR cailper was designed to work as will if not better then 4 pot brakes.
Does this mean I will never get a BBK. No again, I am looking at two combinations now, both with floating rotors, with J-slots, not full length slots.
With almost 4 years of track days under my frame, I use stock calipers, Stock / Raybestos rotors, Castrol SRF brake fluid and PFC-01s and now Wilwood H brake pads. ( parts are replaced as needed)
Plus being an instructor I have driven countless number of Porches, BMWs and other cars on the track. Many have had BBKs of all different makes.
I have even driven a few Porsches 996 RSs ( race prepared). IMO our stock brakes work far better then many BBKs. Then when adding wide sticky front tires, our brakes work far better. Does our equipment last as long? No. Do our brakes look as Cool as a BBK? No
The Corvette 2 pot PBR cailper was designed to work as will if not better then 4 pot brakes.
Does this mean I will never get a BBK. No again, I am looking at two combinations now, both with floating rotors, with J-slots, not full length slots.
12-22-2007, 08:10 AM
#16
Team Owner
I totally agree with drilled/slotted brakes being only bling enhancers. And yet, they look soooooo good! Even though I know the cross-drilled offer no advantage, I still want them on my vehicles. Crazy, eh?
12-22-2007, 09:14 AM
#17
Drifting
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Neither of those articles mentioned or addressed the increased leverage gained from moving the caliber further from the center of rotation, or the increase in swept area gained by going to a larger rotor diameter.
Drilled & Slotted = Bling But I have to admit it does look
Drilled & Slotted = Bling But I have to admit it does look