Firebirdgm2000
05-30-2006, 01:45 AM
I kept the text, but there is no link (one of these days I'll put my site back together....I guess).
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).
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).