Brake rotors

[andyisgood]

Is it worth it to spend an extra 200 dollars on adams rotors with pads and lines than to get the stoptech stage 2 kit with pads, lines and fluid?

[Quattro]

for stoptech, you going with a bbk or just the rotors?

i would go with stoptech

[RVT]

First, I refuse to even touch cross drilled rotors, they are for looks only and can actually hurt braking performance in the long run. You should be able to get slotted rotors from Stoptech which win hands down.
Vince

[Matt@EuropaParts]

Go with the StopTech kit...iirc, they're a floating rotor setup, correct?

[andyisgood]

The Stoptech stage 2 kit I am looking at is this one from ModBargain.
Stoptech Stage 2 (http://www.modbargains.com/_e/B7_A4_Brakes/product/Stoptech_Stage2_Audi_B7_BL2/StopTech_Stage_2_Brake_Upgrade_Audi_A4_B7_.htm)
I really like the drilled drilled slotted option offered by Adam but I see no reason why I should spend the extra 200 and fluids for just the look and no performance gain.
I am concerning about the pad performance as well... I have read through Quattro's brake thread and found no review on stoptech pads but almost all Hawks HPS pad users have a good review...
Should I change out the pad option and get HPS pads? I am looking maybe to do some autocrossing and mostly street driving.

[bartles]

Slotted rotors do give you breaking performance gains, however the drilling is just for the looks. I noticed a huge difference going from stock rotors to slotted/cross drilled, either way you will have much greater stopping power and shorter stopping distances. Go with either HPS or ceramic pads and break dust will be a thing of the past.

[chebyshev]

The M3 competition package (E46 ZCP ) has cross drilled rotors ... is that just for looks too?

[RVT]

The M3 competition package (E46 ZCP ) has cross drilled rotors ... is that just for looks too?

In a word...yes. You could have identical stopping power with slotted rotors, for significantly less money.
But this shouldn't be news to most, as it has been debated time and time again.
You can get quality drilled rotors that will do wonders, but you must shop significantly up-scale. Budget minded buyers are far better staying clear of the cheap versions of drilled and get a reliable slotted system for the same price.

Vince

[bartles]

\You could have identical stopping power with slotted rotors, for significantly less money.
Vince

So are the gains is stopping power I have had from my pads alone?

[Sprode]

Xdrill or slotted rotors improve the heat rejection ability of your brakes. Unless you were seeing fade beforehand (and most non-track going cars do not), you will not see an improvement from a machine treatment of your rotors. Kind of like a bbk: You can see the same results by simply increasing clamping pressure on a smaller rotor.

A BBK works because you can get more arresting moment on the wheel for less clamping force which is less heat. Other than pad material, heat rejection is just about the only property of brakes you have control over, and is pretty much what every mod you see is for.

This guy got it right, and much more concisely than I could have.

http://stason.org/TULARC/vehicles/vw-performance/37-Why-cross-drilled-rotors.html

[ModBargains II]

Is it worth it to spend an extra 200 dollars on adams rotors with pads and lines than to get the stoptech stage 2 kit with pads, lines and fluid?

There are a lot of people who believe that having a 1-piece cross drilled rotor is not advantageous for performance minded individuals. The cross drilled sections tend to weaken the rotor since the thermal expansion plus the lack of material can cause rotors to crack under severe duty.

The Stoptech slotted rotors are a great performance upgrade without the concerns assiciated with a cross drilled setup.

[CleverA4Name]

So ordering a set of Adam's Rotors Drilled/Slotted with Hawk Pads is a bad idea vs. the Stoptech Stage 2 brake kit?

[unh112]

$70 shipping is a little deep though IMO, but it seems like that better setup. Anyone had experience with them? I need brakes soon so i might considered those. The whole kit comes with 4 Rotors correct?

[RVT]

So are the gains is stopping power I have had from my pads alone?

I would say it depends on just what you have, and where you use it.
Both cross drilled and slotted have inherent physical drawbacks, as well as advantages. For cross drilled, I simply feel the drawbacks outweigh any gains unless you are investing in very high end equipment designed for one specific task.

Drawback number one is the reduction in actual surface area for your pads to grab. Stopping power is a process of friction. When pads are clamping on a hole(s) or slot, that area is offering zero friction. Simple common sense says a solid rotor will offer more friction surface than either slotted or drilled.
Drawback number two: I believe "cooling" is misrepresented in the drilled design. A larger piece of metal will take more heat energy to bring up to temp than a smaller piece. It therefore stands that a drilled rotor will heat more quickly as it lacks the extra material to aid in heat dissipation. This higher operating temp can be offset buy pads designed for those temps. Drilled rotors will certainly cool faster once friction is completely removed, however that leads to drawbacks 3 and 4.
Drawback "Rapid" rise and fall in temperatures on metal induce fatigue through what is called "thermal stress". This effectively can alter the molecular structure and like a form of heat treatment, actually begin turning the metal brittle. You see this as micro fractures around the drilled holes. Slower changes in temp are preferred, so a slotted or solid wins again.
Drawback number four: Brake pads are designed to function best at a specified temperature range. Example: Race pads work well on high temp rotors, but will not stop you while backing out of your driveway on a cold morning. They fail only because they are outside their design temps. OEM pads however are designed for lower temps, which is why they fail quickly in a high temp track environment. Like tires, you need to buy a pad for your specific task. Any pad considered a "jack of all trades", can always be beaten by one designed for a specific task.
Drawback five: Most "Cheap" drilled rotors have not been properly heat treated AFTER the drilling process. Taking a bulk Chinese pot-metal rotor, punching a bunch of holes, then surfacing the contact area may produce a cool look, but the amount of stress the vendor has pre-loaded into the material is a formula for disaster. Ideally, one would heat treat the rotor afterward to relieve (also called "normalize") any possible stress risers created in the milling process.

As I am not a brake expert, this is simply my opinion based on my knowledge of metallurgy and thermal properties of metal overall. I hope this helps, and welcome intelligent debate, as there may be a minor flaw or two in my reasoning against drilled rotors, but I do feel they are not the "holy grail" the younger crowd has convinced themselves of.
My personal preference in the home consumer market (ie non-race team budgets) is a set of slotted Cryo rotors.

peace
Vince

[NastyNate]

I would say it depends on just what you have, and where you use it.
Both cross drilled and slotted have inherent physical drawbacks, as well as advantages. For cross drilled, I simply feel the drawbacks outweigh any gains unless you are investing in very high end equipment designed for one specific task.

Drawback number one is the reduction in actual surface area for your pads to grab. Stopping power is a process of friction. When pads are clamping on a hole(s) or slot, that area is offering zero friction. Simple common sense says a solid rotor will offer more friction surface than either slotted or drilled.
Drawback number two: I believe "cooling" is misrepresented in the drilled design. A larger piece of metal will take more heat energy to bring up to temp than a smaller piece. It therefore stands that a drilled rotor will heat more quickly as it lacks the extra material to aid in heat dissipation. This higher operating temp can be offset buy pads designed for those temps. Drilled rotors will certainly cool faster once friction is completely removed, however that leads to drawbacks 3 and 4.
Drawback "Rapid" rise and fall in temperatures on metal induce fatigue through what is called "thermal stress". This effectively can alter the molecular structure and like a form of heat treatment, actually begin turning the metal brittle. You see this as micro fractures around the drilled holes. Slower changes in temp are preferred, so a slotted or solid wins again.
Drawback number four: Brake pads are designed to function best at a specified temperature range. Example: Race pads work well on high temp rotors, but will not stop you while backing out of your driveway on a cold morning. They fail only because they are outside their design temps. OEM pads however are designed for lower temps, which is why they fail quickly in a high temp track environment. Like tires, you need to buy a pad for your specific task. Any pad considered a "jack of all trades", can always be beaten by one designed for a specific task.
Drawback five: Most "Cheap" drilled rotors have not been properly heat treated AFTER the drilling process. Taking a bulk Chinese pot-metal rotor, punching a bunch of holes, then surfacing the contact area may produce a cool look, but the amount of stress the vendor has pre-loaded into the material is a formula for disaster. Ideally, one would heat treat the rotor afterward to relieve (also called "normalize") any possible stress risers created in the milling process.

As I am not a brake expert, this is simply my opinion based on my knowledge of metallurgy and thermal properties of metal overall. I hope this helps, and welcome intelligent debate, as there may be a minor flaw or two in my reasoning against drilled rotors, but I do feel they are not the "holy grail" the younger crowd has convinced themselves of.
My personal preference in the home consumer market (ie non-race team budgets) is a set of slotted Cryo rotors.

peace
Vince

Vince,
With all due respect, I would like to inquire as to your education/occupation. My intent here is not to discredit, but to weigh your observations with what I understand about the physics of the braking situation.

You draw attention to the friction that is the heart of the braking process, yet you pay no attention to the differences between static and dynamic friction. The key factor that affects slotted/drilled/dimpled rotors is that they increase the amount of static friction that is generated during the braking process. Static friction represents the energy required to BEGIN sliding between two surfaces. Dynamic friction is the energy required to continue the sliding.

It is well-known that the coefficient of static friction is generally (if not always) greater than the coefficient of dynamic friction.

The impact of this difference is that the introduction of new surfaces, whether the result of a drilled hole or a machined dimple/slot is that the braking power is increased due to the higher amount of energy absorbed by the braking process.

Vince,
I know that you frown upon the showiness of machined rotors, but you are dead wrong in your reasoning that a solid surface offers more friction than a machined surface. I will grant that the greater amount of friction generated will wear brake pads faster, but you'd have to expect that trade-off for greater stopping power.

[NastyNate]

Xdrill or slotted rotors improve the heat rejection ability of your brakes. Unless you were seeing fade beforehand (and most non-track going cars do not), you will not see an improvement from a machine treatment of your rotors. Kind of like a bbk: You can see the same results by simply increasing clamping pressure on a smaller rotor.

A BBK works because you can get more arresting moment on the wheel for less clamping force which is less heat. Other than pad material, heat rejection is just about the only property of brakes you have control over, and is pretty much what every mod you see is for.

This guy got it right, and much more concisely than I could have.

http://stason.org/TULARC/vehicles/vw-performance/37-Why-cross-drilled-rotors.html

Sprode, this guy, although articulate, does not know what he's talking about. It is NOT just about heat dissipation.

Why would cross-drilled rotors be banned from events if they don't enhance performance? I HIGHLY DOUBT that it's due to safety concerns over cracked rotors.

[RVT]

Vince,
With all due respect, I would like to inquire as to your education/occupation. My intent here is not to discredit, but to weigh your observations with what I understand about the physics of the braking situation.

You draw attention to the friction that is the heart of the braking process, yet you pay no attention to the differences between static and dynamic friction. The key factor that affects slotted/drilled/dimpled rotors is that they increase the amount of static friction that is generated during the braking process. Static friction represents the energy required to BEGIN sliding between two surfaces. Dynamic friction is the energy required to continue the sliding.

It is well-known that the coefficient of static friction is generally (if not always) greater than the coefficient of dynamic friction.

The impact of this difference is that the introduction of new surfaces, whether the result of a drilled hole or a machined dimple/slot is that the braking power is increased due to the higher amount of energy absorbed by the braking process.

Vince,
I know that you frown upon the showiness of machined rotors, but you are dead wrong in your reasoning that a solid surface offers more friction than a machined surface. I will grant that the greater amount of friction generated will wear brake pads faster, but you'd have to expect that trade-off for greater stopping power.
I thank you for the opportunity to discuss it further.
As for my background, I am a certified aircraft mechanic (A&P), although i have not worked in the field since the late eighties.
Autocross and track merely have been a hobby for me since about 1990.

My analysis of friction and braking power comes from a more simpler understanding of physics. (You will most likely be over my head with discussions of static and dynamic friction.)

My view is this... Lets take a 2 inch cube, made of metal(represents the pad), and lay it on a flat metal surface (representing the rotor). We have 4 square inches of surface to surface contact. Assuming no pressure other than the weight of the cube, how much friction (ability to resist moment) will the cube exert when pulled across the surface? This resistance is then recorded as a measurable transfer of energy between objects. Logic follows that if I place the cube over a hole drilled in the same metal surface, then I now have less than 4 square inches of contact patch, while maintaining equal pressure as before, and the amount of energy transfer will be reduced by the area of the hole. right? Regardless of extended forces occur during the braking process, this analogy should hold true across the board.

I love to learn, and have no problem getting corrected by more in-depth information, but I think the leap to static/dynamic principals will still need to fit within the basic physics I just described, correct?

Again, I try to see things from a simplistic point of view. often that is all the further I need to go for an answer...

Thoughts?
Vince

[Sprode]

Sprode, this guy, although articulate, does not know what he's talking about. It is NOT just about heat dissipation.

Why would cross-drilled rotors be banned from events if they don't enhance performance? I HIGHLY DOUBT that it's due to safety concerns over cracked rotors.

They DO enhance performance. Perhaps you underestimate how important heat dissipation is?

[NastyNate]

I thank you for the opportunity to discuss it further.
As for my background, I am a certified aircraft mechanic (A&P), although i have not worked in the field since the late eighties.
Autocross and track merely have been a hobby for me since about 1990.

My analysis of friction and braking power comes from a more simpler understanding of physics. (You will most likely be over my head with discussions of static and dynamic friction.)

My view is this... Lets take a 2 inch cube, made of metal(represents the pad), and lay it on a flat metal surface (representing the rotor). We have 4 square inches of surface to surface contact. Assuming no pressure other than the weight of the cube, how much friction (ability to resist moment) will the cube exert when pulled across the surface? This resistance is then recorded as a measurable transfer of energy between objects. Logic follows that if I place the cube over a hole drilled in the same metal surface, then I now have less than 4 square inches of contact patch, while maintaining equal pressure as before, and the amount of energy transfer will be reduced by the area of the hole. right? Regardless of extended forces occur during the braking process, this analogy should hold true across the board.

I love to learn, and have no problem getting corrected by more in-depth information, but I think the leap to static/dynamic principals will still need to fit within the basic physics I just described, correct?

Again, I try to see things from a simplistic point of view. often that is all the further I need to go for an answer...

Thoughts?
Vince

I include myself in this statement when issuing the warning: NERD ALERT!

I appreciate the discourse as well, and I am certainly no braking engineer. I studied Materials Science and Engineering in school, so I'm drawing from that hazy experience...

The problem with your cube across a surface analogy is that it doesn't account for new surfaces and the energy expended when surfaces meet. Any equation on friction/energy has two parts: one for breaking the static friction and the other for maintaining dynamic friction.

Cross-drilled rotors did not start as a way to make a car look better/different. They were introduced to increase braking friction and to dissipate heat. Slotted rotors work on the same concept. It's generally acknowledged that slotted rotors perform better than blanks. The reason is the re-introduction of friction (read: static friction) to the braking process. Slotted rotors more efficiently accomplish this due to the consistent "re-introduction" of friction caused by the linear slot.

I haven't talked yet about what I chose for my new rotors, but here goes. I got the AR dimpled/slotted rotors for a few reasons. Slotting gives the best/most consistent performance gains, and dimpling gives a little heat dissipation and good looks. For me, drilling is just a touch to gaudy, although I love seeing it on other cars. I have no trepidation about putting these rotors on my car. I believe they will increase braking performance and improve looks. They may shorten brake pad life, but I do not care.

[Sprode]

Vince,
With all due respect, I would like to inquire as to your education/occupation. My intent here is not to discredit, but to weigh your observations with what I understand about the physics of the braking situation.

You draw attention to the friction that is the heart of the braking process, yet you pay no attention to the differences between static and dynamic friction. The key factor that affects slotted/drilled/dimpled rotors is that they increase the amount of static friction that is generated during the braking process. Static friction represents the energy required to BEGIN sliding between two surfaces. Dynamic friction is the energy required to continue the sliding.

It is well-known that the coefficient of static friction is generally (if not always) greater than the coefficient of dynamic friction.

The impact of this difference is that the introduction of new surfaces, whether the result of a drilled hole or a machined dimple/slot is that the braking power is increased due to the higher amount of energy absorbed by the braking process.

Vince,
I know that you frown upon the showiness of machined rotors, but you are dead wrong in your reasoning that a solid surface offers more friction than a machined surface. I will grant that the greater amount of friction generated will wear brake pads faster, but you'd have to expect that trade-off for greater stopping power.

Wow. Static and dynamic friction have no place here. Braking is a purely dynamic event. The rotors are always turning. The only time static friction would be involved is if you are brake boosting off the line.

[NastyNate]

They DO enhance performance. Perhaps you underestimate how important heat dissipation is?

I'm not hating on heat dissipation... I'm in agreement that braking performance is a combination of stopping power and fade resistance. My point was that heat disspation is not the sole factor in braking. Clearly stopping power is the priority and resistance to brake fade is dependent on the disspation of heat.

[Sprode]

I include myself in this statement when issuing the warning: NERD ALERT!

The problem with your cube across a surface analogy is that it doesn't account for new surfaces and the energy expended when surfaces meet. Any equation on friction/energy has two parts: one for breaking the static friction and the other for maintaining dynamic friction.

Cross-drilled rotors did not start as a way to make a car look better/different. They were introduced to increase braking friction and to dissipate heat. Slotted rotors work on the same concept. It's generally acknowledged that slotted rotors perform better than blanks. The reason is the re-introduction of friction (read: static friction) to the braking process. Slotted rotors more efficiently accomplish this due to the consistent "re-introduction" of friction caused by the linear slot.

I haven't talked yet about what I chose for my new rotors, but here goes. I got the AR dimpled/slotted rotors for a few reasons. Slotting gives the best/most consistent performance gains, and dimpling gives a little heat dissipation and good looks. For me, drilling is just a touch to gaudy, although I love seeing it on other cars. I have no trepidation about putting these rotors on my car. I believe they will increase braking performance and improve looks. They may shorten brake pad life, but I do not care.

You are not thinking about friction right. Once you overcome static friction, the only applicable term is the dynamic friction term. Those are the definitions.

[NastyNate]

Wow. Static and dynamic friction have no place here. Braking is a purely dynamic event. The rotors are always turning. The only time static friction would be involved is if you are brake boosting off the line.

Interesting. So I would love to hear your reasoning on why rotors EVER get machined. To my knowledge (which may be limited), slotted rotors are known to increase stopping power at any temperature. I'm 99.9 percent sure it's not because of heat dissipation. Are the only advantages to machined rotors gained when the rotors get hot?

[Sprode]

You guys are going back and forth about a couple things that aren't quite on point.

The link I posted shows the reasoning behind machining your rotors. When properly designed and applied, they provide a definite advantage because (ignoring the gassing effect) the amount of heat dissipated by the machining is greater than the extra heat generated by the extra pedal pressure necessary to keep the same force on the brake.

Whether or not someone purchased poorly constructed rotors is their own deal. This technology exists because it works. The problem is that the cost in doing it right is probably not worth it for a street car.

EDIT: A brake system converts the entirety of a cars kinetic energy to heat, over and over, in rapid succession. Any increase in heat dissipation is key to get properly performing brakes. You can only stop the car as fast as you can cool the brakes.

[NastyNate]

You are not thinking about friction right. Once you overcome static friction, the only applicable term is the dynamic friction term. Those are the definitions.

Said it in my prior post, but what about slotted rotors? It's clearly not about heat disspation. I might not be using the right terminology, but I believe the concept is sound.

After doing a little more research, the "experts" say that the reason for increased performance is that the "unwanted gases and particles" are channeled away from the braking surface. This effect is seen with any machined surface. So, that means that machined surfaces increase friction of any variety by putting the brake pad directly in contact with the rotor without any brake dust in between to muck up the process.

[Sprode]

Interesting. So I would love to hear your reasoning on why rotors EVER get machined. To my knowledge (which may be limited), slotted rotors are known to increase stopping power at any temperature. I'm 99.9 percent sure it's not because of heat dissipation. Are the only advantages to machined rotors gained when the rotors get hot?

You will find mostly anecdotal evidence of butt-dyno increases in stopping power when people put on new rotors. Most of the time they aren't doing back to backs with new blank rotors to see that new parts will get you some nice firm stopping power as well. You have all new brake parts and you stop better? This seems quite plausible. Are you stopping better from 45-0 every now and then than you would with new oem brake gear? Probably not. Will you stop better from 120-0? I'd bet so.

[Sprode]

Said it in my prior post, but what about slotted rotors? It's clearly not about heat disspation. I might not be using the right terminology, but I believe the concept is sound.

After doing a little more research, the "experts" say that the reason for increased performance is that the "unwanted gases and particles" are channeled away from the braking surface. This effect is seen with any machined surface. So, that means that machined surfaces increase friction of any variety by putting the brake pad directly in contact with the rotor without any brake dust in between to muck up the process.

Slotting and xdrilling truly serve the same purposes. If you go back to the link I posted, it says pretty much that, and heat dissipation.

[NastyNate]

You will find mostly anecdotal evidence of butt-dyno increases in stopping power when people put on new rotors. Most of the time they aren't doing back to backs with new blank rotors to see that new parts will get you some nice firm stopping power as well. You have all new brake parts and you stop better? This seems quite plausible. Are you stopping better from 45-0 every now and then than you would with new oem brake gear? Probably not. Will you stop better from 120-0? I'd bet so.

I agree that when looking at all new parts, stopping power is pretty much always better per the butt-dyno. I will also give you the benefit of the doubt that you're NOT saying that blanks are better than machined rotors in terms of performance.

[Sprode]

Before you ask, I've actually got a Masters in Mechanical Engineering, so I'm not talking out of my ass. :P

[NastyNate]

Slotting and xdrilling truly serve the same purposes. If you go back to the link I posted, it says pretty much that, and heat dissipation.

OK. Good conversation though. I like your conclusion.

[NastyNate]

Before you ask, I've actually got a Masters in Mechanical Engineering, so I'm not talking out of my ass. :P

Yup, me neither. Your arguments make sense, and I didn't mean otherwise when I disparaged your quote. Sometimes it's better to cite your own knowledge than that of an interwebz post.

[Sprode]

I agree that when looking at all new parts, stopping power is pretty much always better per the butt-dyno. I will also give you the benefit of the doubt that you're NOT saying that blanks are better than machined rotors in terms of performance.

I am sorry if I am being unclear. I definitely think a properly machined rotor will perform as well or better in almost all situations.

[Sanjman]

Random food for your thought...

F1 racing cars do not carry cross drilled or slotted rotors however use some kind of carbon composites to alleviate what *none* of you really have to experience on metal rotors unless you are HEAVILY tracking. It is sick how the rotors turn scorching red hot when the driver is in the corners.

http://farm3.static.flickr.com/2359/2210308705_7f03589940.jpg

http://autoracingworld.files.wordpress.com/2008/12/brake-pads.jpg

BACK TO THE TOPIC:
In theory, *some* of you might be correct in some ways, but really it comes down to looks for the joe in these forums.

options:
-BBK for performance
-anything else for looks.

Answer for OP: No it is not worth it. Get Stoptech's.

[RVT]

The conversation is actually fairly good, and I wish this was over in the tech section so not to impose on those that do not care. What can I say....
Still, this has some interesting info to it, and I would like to see us refrain from rude comments (I guess I don't understand the "nerd alert" comment).

Sprode - It certainly can't hurt to have an engineer on board the discussion to help offer a more refined edge to the data presented. Sadly, at age 50, I've known and cleaned up after many "Engineers" that lacked practical knowlege or common sense... so please don't ask me to take you as "gospel" until I can get to know you better. I'm glad your here so please keep contributing.

It has been generally accepted that the origins of slotted and drilled rotors was to assist with out-gassing of the pads in the early years (60's?). Pads generating out-gasses have long since been gone, so the purpose for the original design is no longer relevant, correct?
Additional gains can be looked at, such as the ability to wipe foreign material or water from the mating surfaces quickly, which anyone that has gotten a pebble wedged in there knows can hamper efficiency and eat rotors. So self cleaning is a gain over a solid rotor.
Weight reduction is another.
I think some of these are what push high end cars to use them. Then again, high end cars develop the entire braking system around the needs of the calipers and rotors. Extra clamming force, extra cooling ducts, (not to mention much deeper pockets to replace expended items more frequently) make the shift to those type rotor of no consequence.

The common street car did not have that level of forethought put into an OEM brake system.

Speaking of high end systems, Sanjman bring home a point I have been out surfing for an answer on... What DO the big boys run? NASCAR? Formula 1? Slotted? Drilled? Solid? Not having luck in my hunt yet.

?
V

Interesting read...
http://www.8thcivic.com/forums/suspension-brakes/92039-cross-drilled-rotor-myths-dissolved.html

[NastyNate]

The conversation is actually fairly good, and I wish this was over in the tech section so not to impose on those that do not care. What can I say....
Still, this has some interesting info to it, and I would like to see us refrain from rude comments (I guess I don't understand the "nerd alert" comment).


Vince, I was basically saying the same thing as you regarding the fact that this discussion should have taken place in the tech forum. There aren't that many conversations like this in the B7 A4 section. If you took offense, then I apologize.

Good point, it would be interesting to see what the big boys run. I would imagine that their budgets allow them to use materials that are significantly better at generating braking friction while allowing as much heat dissipation as possible. I would also imagine that they probably have cooling systems for the brakes that would clearly be impractical for us.

Sanjman made a pretty good point, in that for 99% of us here (let alone the general population), machined vs. solid doesn't really matter. I put myself squarely into that 99% for now, as I have yet to track the car. In general, I agree that the gains, if any, that you get solely from a rotor swap are not enough to create a tracking monster. Clearly that's what BBKs are for.

[Sprode]

It is hard to argue with (hopefully accurate quotes from ) brake manufacturers, but I'll throw some parting shots out. I tried not to incorporate outgassing in my previous posts because that truly is an outdated reason.

1. Formula brakes these days are a lot more like clutch material than standard brakes.

http://farm4.static.flickr.com/3189/3020446945_272fba2cfc.jpg

These are not conducive to ANY kind of machining at all.

2. I would argue that while you do reduce thermal capacitance, you certainly increase surface area as well as convective cooling through the rotor. A similar use is the application of internally routed cooling water veins through turbine blades. Seems like mostly the same thing to me.

3. I would lastly argue that "cheese grater effect" referred to in one of the links would have the same effect on cleaning the pad as a slotted rotor.

I clearly do not know from personal investigation, but this is what jumped out at me reading some of the previous articles.

EDIT: Reading some of that 8thcivic post, a lot of the guys arguments are fallacious, misleading, or ambiguous. For example: He says the number one reason to have a BBK is to have a bigger pad with more area on the rotor. This is FALSE. The reason to get a bbk is the increased diameter of the rotor. For the same clamping force, you get more counter rotation (longer lever arm) on the brake. Throws the whole article into question for me...

[chebyshev]

*sits back and absorbs all this knowledge*

[ModBargains II]

It is hard to argue with (hopefully accurate quotes from ) brake manufacturers, but I'll throw some parting shots out. I tried not to incorporate outgassing in my previous posts because that truly is an outdated reason.

1. Formula brakes these days are a lot more like clutch material than standard brakes.

These are not conducive to ANY kind of machining at all.

2. I would argue that while you do reduce thermal capacitance, you certainly increase surface area as well as convective cooling through the rotor. A similar use is the application of internally routed cooling water veins through turbine blades. Seems like mostly the same thing to me.

3. I would lastly argue that "cheese grater effect" referred to in one of the links would have the same effect on cleaning the pad as a slotted rotor.

I clearly do not know from personal investigation, but this is what jumped out at me reading some of the previous articles.

EDIT: Reading some of that 8thcivic post, a lot of the guys arguments are fallacious, misleading, or ambiguous. For example: He says the number one reason to have a BBK is to have a bigger pad with more area on the rotor. This is FALSE. The reason to get a bbk is the increased diameter of the rotor. For the same clamping force, you get more counter rotation (longer lever arm) on the brake. Throws the whole article into question for me...


The main benefit of a BBK system is for the increased modulation feel (multiple pistons), increase the ability to dissipate heat (floating 2-piece rotors with vanes), and the shortened stopping distance (larger piston volume on the BBK kits versus standard OEM brakes). This is very beneficial for the guys that are already fading their stock brake components even with race pads and upgraded fluids.

[hudock08]

knowledge overload right now. i like it. just when i thought static and dynamic only referred to types of ropes i used in firefighting. i was WAY off. haha

[Sprode]

I believe this muddles the issue.

BBKs do have these properties, but they are not anything that could not be retrofit into an OEM system. The things you have listed are design features built into a more expensive than stock braking system. They are not inherent physical gains.

My point is, if you did all of these things and offered them in the same diameter as OEM brakes, they would perform better than OEM. The point of a larger diameter rotor is the lever arm.

No argument on multiple pistons increasing braking feel: But that has little to do with the brake actually being bigger.

The increased heat dissipation is also true of course. Bigger brake is more surface area. The rotor technology, again, could be applied to an oem style brake and see the same gains.

But truly, the best gains are based on the increased lever arm. You get a multi percent increase in stopping power for no extra heat and negligible increase in rotating mass.

I have not been through the numbers on Audi's, but for example: Supras run a 12.1" stock rotor. Lots of ppl run the 14" brembo upgrade. That is a (14/12.1=1.15) 15% increase in breaking power at a given pedal pressure. No extra heat, no drawbacks except for the rotating mass. Hard to beat the gains when physics is on your side.

[RVT]

Wow,

NastyNate - As I later thought about it, I had to surmise you are probably right, I guess I am some kind a nerd. I simply love the technical side of anything, and read constantly. Hell, my wife just got diagnosed with Leukemia and I found myself out reading full scale medical journals on the subject (Like I have a clue about biology [rolleyes] ) Still, it was written with technical accuracy, so off I went thinking I was going to put understanding to it (Obvious fail [headbang])!
Electronics Tech- Aircraft Mechanic- Network administrator- Nerd.... yup, maybe it fits after all...[>_<]

Sprode - I think your right standing back from the linked article and scrutinizing some of the wording. I only followed a few of the references and quotes to attempt to validate them with moderate success, but certainly did not take time to cross check them all. The net is full of "authoritative" writings, right up until you find out some 13 year old wrote it! Much of his argument does support my understanding of brakes in general. The one Cheese grater comment does seem a little odd, but as we know drilled holes to be a point where stress fractures begin, I can see the jagged fracture lines eminating from those holes being more of an abrasive than the actual holes themselves.
This is why I believe in proper heat treatment should be done after any machining (which I'm pretty sure the big name companies do) to normalize and relieve stress created by the process. But I also believe ANY cross drilling must be done with the hole being camfered. You will find most cheap rotors do neither.
I cannot feel slotted or drilled offer anything but worst heat disipation thanks to the amount of metal removed which would otherwise soaked up the excess heat. The "Heatsink" concepts work well here, where the more metal, the better the dispursion, the less, the more concentrated the heat.

So I'm still a believer that in the real world, solid rotors offer the greatest stopping power and best heat resistance over both slotted and drilled. I have run the PowerSlot slotted Cryos (recently bought by StopTech) in the past. My choice for slotted was to address the fact I live in the Pacific Northwest (IE torrential rains and standing water) with the belief of rapid water dissipation without the concerns of cracking, while accepting the fact I had less pad to rotor contact for that decision.

BBK is a whole different discussion, and i believe you are correct on the leverage topic. I'm also a believer in low unsprung weight (hence my 18lb Enkies [up]) so would not leap on a BBK system until my driving habits and better pads showed me an OEM sized solution could no longer be obtained.

[Sprode]

The only comment on that is that I believe you confuse heat dissipation (ability to reject energy to the environment) and thermal capacitance (how much energy it takes to increase the temperature). Solid rotors clearly carry the most capacitance. The amount of induced convective cooling that runs through the drilled holes or slots is going to be speed dependent and would require a simulator to get specific answers. I've got to say that in my mind, there is pretty significant cooling that would take place in the internal channels between ~100F turbulent air and 1000F brakes, changing the "effective capacitance over time". Think about how a FMIC works, and why its not a solid brick.

I fear that if I keep posting, I should just give up and start writing a paper.

[SilverBullets]

I have nothing technical to add... Im just a 24 year old IT Auditor.. but from an experience standpoint (this being 15+ track weekends over the past 6 years) slotted rotors crack under extreme conditions. It happened on my dad's 996 C4 (it happened twice) and it happened on his 997 C2S. Once it happened the 2nd time on the 996, he decided this was something he loved and he invested in a fully built 944 S2 track car. My dad competes in NASA and PCA racing. He runs Frozen Rotors which if I remember correctly are not slotted. I do know the slotting is supposed to help with Heat Dissipation which cools the rotor which means better initial bite when braking.... but that has already been covered

[RVT]

I fear that if I keep posting, I should just give up and start writing a paper.
I'd read it!
Personally, I'm glad you continue to stick to your guns. The deeper I dig and the more writeups I find, the more your heat dissipation via convection becomes the more dominant truth. It seem to constantly outweigh my thoughts of mass for heat distribution by a large factor (maybe 4 or 5 to 1? yeash!) Thanks for the push. [hail] Had no idea you could dissipate that much heat through drilling, as my original thinking was that hot air was expelled from the interior! Your reference to a centrifugal turbine was a great nudge to keep me digging. Turns out that the inside vane area is not a positive pressure, but a negative. Duh...[headbang] I now realize that that it is [U]cool air being drawn IN through the holes (thanks to the negative pressure at the outside circumference of the vents) . Thanks for the wisdom and effort to clairify.

As an added note, I found a writeup that both the holes and slots can actually assist with glaze removal (via that cheese-grater effect we were questioning). As the slots wipe the whole pad, and the holes only part, they felt slots won in that respect.

Here is the read, but still referenced many contributes that needed validating.
http://home.wavecable.com/~vtucker/A4/rotors.pdf

Another very detailed article on rotor heat more up your ally than mine: http://cds.comsol.com/access/dl/papers/1606/Asfour_pres.pdf



from an experience standpoint slotted rotors crack under extreme conditions.
Interesting... Slotted rotors are not known for cracking easily unless improperly manufactured. I have seen several cheap ones on the market that are a disaster waiting to happen... One eBayer touts "our unique V grove design self cleans dust and dirt" , yet anyone with understanding of metal stresses knows you do not have sharp points cut in metal as this is where stress fractures actually begin. Proper slots are smooth rounded channels cut into the material, "Square" cut channels/slots or "V" cut channels is simply a shoddy design and will most certainly lead to failure. Not saying that is what your dad had, but those inexpensive rotor do exist out there simply waiting for the unwary buyer to grab up.

V

[Sprode]

Where did you find these articles? I was looking for stuff like this but came up empty.

Lots of typos in the first one make me sad. I'll decide when i'm not drinking.