Cross drilled rotors, better or not?

[SkylineUSA]

Some of you guys are just Lemmings, if you believe what you believe so be it.

Seth,

How many racing events have you been in? Where do you get your information from?

[SkylineUSA]

READ! Maybe you can be enlightened, maybe not

By the way I did not post that cross drilled rotors were developed in the 50's, that was posted by a mechanical engineer. Someone who studied the theories, not just read some adverts. MmmmK(Mr. Macky).


quote:
--------------------------------------------------------------------------------
I am going to be opinionated here for a bit, just like in the other post (the DZ coilover post). I am kinda tired of unqualified answers, so I speak from a personal and professional experience with brakes.
Here we go.
--------------------------------------------------------------------------------

My advice - pick a new profession. Something simple. Perhaps - a Wal-Mart greeter. Your qualifications are almost adequate for that.

quote:
--------------------------------------------------------------------------------
Crossdrilled rotors-by design, crossdrilled rotors were designed for track use. Why? Because, when you drill holes in your rotors, they are designed to dissipate heat (not to rid of brake dust as most people think).
--------------------------------------------------------------------------------

I found the root of your problem. It is right here. You don't know the definition of "dissipate". You also don't understand the interaction between a rotor and the pads. Here is how it works. The friction between the pad and rotor is what causes you to stop. This friction converts your forward energy into heat (remember Einstein: Energy is neither created nor destroyed, it is converted). Now that heat is a bad thing. Yes it is bad for the rotors but it is a lot worse for the pads. A warped rotor will still stop the car - it will just feel like shit. Overheated pads however WILL NOT stop the car. It is here where the rotors secondary responsibility comes in. Its job now is to DISSIPATE the heat away from the pads and DISPERSE it through itself. Notice that DISSIPATE and DISPERSE are interchangeable? Once the heat is removed from the pad/surface area it is then removed. Notice where the removal falls on the list of duties? That's right - number 3. Here is the list again. Memorize it because I will be using it a lot in this post:

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle

#2 DISSIPATE the heat

#3 REMOVE the heat from the brake system

Let's look more in-depth at each step now shall we? No? Too bad assclown we are doing it anyway.

#1 Maintains a coefficient of friction with the pad to slow the forward inertia of the vehicle:
This one is pretty simple and self-explanatory. The rotor's surface is where the pads contact and generate friction to slow the vehicle down. Since it is this friction that causes the conversion of forward acceleration into deceleration (negative acceleration if you want) you ideally want as much as possible right? The more friction you have the better your stopping will be. This is reason #1 why BIGGER brakes are the best way to improve a vehicle's stopping ability. More surface area on the pad and the rotor = more friction = better stopping. Does that make sense Ace? Good. Let's move on.

#2 DISSIPATE The Heat:
Let's assume for a second that the vehicle in question is running with Hawk Blue pads on it. The brand doesn't really matter but that is what I am using as my example. They have an operating range of 400 degrees to 1100 degrees. Once they exceed that 1100 degree mark they fade from overheating. The pad material gets too soft to work effectively - glazing occurs. This means that a layer of crude glass forms on the surface of the pad. As we all know glass is very smooth and very hard. It doesn't have a very high coefficient of friction. This is bad - especially when I am coming down the back straight at VIR at 125MPH. Lucky for us the rotor has a job to do here as well. The rotor, by way of thermal tranfer DISSIPATES the heat throughout itself. This DISSIPATION lessens the amount of heat at the contact area because it is diluted throughout the whole rotor. The bigger the rotor the better here as well. The more metal it has the more metal the heat can be diluted into. Make sense? This isn't rocket science here d00d.

#3 REMOVE the heat from the brake system:
Now comes your favorite part of the process. This is what you thought DISSIPATION was. It is ok. I will allow you to be wrong. This is the step where the rotor takes the heat it DISSIPATED from the pads and gets rid of it for good. How does it do this? By radiating it to the surface - either the faces or inside the veins. It is here where cool air interacts with the hot metal to cool it off and remove the heat. Once again there is a reoccuring theme of "the bigger the better" here. The bigger the rotor, the more surface area it will have which means more contact with the cooling air surrounding it. Got it? Good.

Now let's look at why cross-drilling is a bad idea.

First - as we have already established, cross-drilling was never done to aid in cooling. Its purpose was to remove the worn away pad material so that the surfaces remained clean. As we all know this doesn't have much of a purpose nowadays.

Next - In terms of cooling: Yes - x-drilling does create more areas for air to go through but remember - this is step 3 on the list of tasks. Let's look at how this affects steps 1 and 2. The drilling of the rotor removes material from the unit. This removal means less surface area for generating surface friction as well as less material to accept the DISSIPATED heat that was generated by the friction. Now because of this I want to optimize step one and 2 since those are the immediate needs. If it takes longer for the rotor to get rid of the heat it is ok. You will have a straight at some point where you can rest the brakes and let your cooling ducts do their job. My PRIMARY concern is making sure that my car slows down at the end of the straight. This means that the rotor needs to have as much surface as possible to generate as much friction as possible and it needs to DISSIPATE the resulting heat AWAY from the pads as quick as possible so they continue to work. In both cases x-drilling does nothing to help the cause.

Now let's talk about strength - and how x-drilled rotors lack it. This one is simple. Explain again just how drilling away material/structure from a CAST product DOES NOT weaken it? Since you are obviously a man of great knowledge and experience surely you have seen what can happen to a x-drilled rotor on track right? Yes it can happen to a non-drilled rotor as well but the odds are in your favor when pimpin' bling-bling drilled y0! Since you are also an expert on thermodynamics why not explain to the group what happens to a cast iron molecule when it is overheated. I will give you a little hint - the covalence bonds weaken. These bonds are what hold the molecules together boys and girls. You do the math - it adds up to fractures.

So why don't race teams use them if they are so much better? Consistency? Hmmmm . . . no. I am gonna go with the real reason her chodeboy. It is because of several factors actually. They are as follows but in no particular order:

- Less usable surface area for generating friction
- Less material to DISSIPATE the heat away from the pads
- Less reliable and they are a safety risk because of fatigue and stress resulting from the reduced material

And what are the benefits? Removal of particulate matter and enhanced heat removal. I gotta tell ya - it is a tough choice but I think I am going to stick with the safe, reliable, effective-for-my-stopping needs solution Tex.

Finally let's talk about you. You should be ashamed of yourself. You are obviously regarded as a sort of demigod here. I am not quite sure why but the little toadie sticking up his fingers and saying "don't argue with THE MAN" is evidence that there are quite a few lemmings here just waiting to follow you off the nearest cliff. A vendor should really take knowledge and understanding of the products he recommends and sells a little more seriously. Further - who the fvck quotes Super Street as a reliable source of tech info of any kind? That smut is as useful for auto tech as is Cosmopolitan. Only a fool would EVER use claims made by that publication as facts in an argument. Your bad advice is going to get one of these new guys killed because they think you know your shit, they are going to take your advice, and then they are going to careen head on into a retaining wall at 120MPH because the part YOU recommended them failed at race speeds. Fvck you shithead! You may not care if that blood is on your hands but I will do what I can to make sure it isn't on mine.

Most of you lemmings will stick your little fingers up at me but I know a few of you will read my words and the words of the others here who are trying to set the record straight. I don't expect any of you to take any of this advice here as scripture. I urge you all to go and do some research. Talk to more than just the dickhead in this thread. Find out what people who ACTUALLY race are doing and why they are doing it. I have news for you all. There is no "better" idea. It has all been done before. If it worked people would do it now.

Commence the banning since I am not willing to swing from the jock of this fool.


__________________
I hate choads who talk out there ass.

[SilverY2KCivic]

Degrading someone to make a point is kidergarden sh!t, you being the intelligent one you are should already know that, Mr. Skyline.

Anywho, I'm not going to junk my slotted rotors because of one's opinion, I'll let my ACTUAL experience with them be the judge of that, which so far is swinging more in the direction of my slotted rotors, than my stock POS rotors they replaced. What do people use that race? Well drilled rotors maybe not suited for 200mph F1, Indy or NASCAR vehicles, but it's what MANY (including some of the most experienced) are using on their cars in auto-cross/road racing. How do I know this? Well I auto-x myself, and I doubt the "pros" at this kind of sport would use slotted (what I see more of) rotors if they weren't all they were cracked up to be. You still didn't explain why car manufactures equip cars with drilled rotors. Answer the REAL questions at hand here, and maybe someone will listen.

[SkylineUSA]

Degrading someone to make a point is kidergarden sh!t, you being the intelligent one you are should already know that, Mr. Skyline.

Who is degrading, who? I am not using vulgarity to make my point.

"I am not sure I know the answer to the Porsche question either. My guess however is that it lies somewhere in the metalurgy of the materials they use. Perhaps they are heat treated or cryo-treated or utilize a different casting process to manufacturer them. As SlowSER has said however - they are still prone to failures as with any other x-drilled application. Why Porsche has decided to use them is beyond me. Ferrari has used them in the past as well.

In any event I can tell you that the pieces installed on the GT2 are significantly different than the stock blanks that are drilled, re-badged and sold to kids as "performance" items."

This was posted by a guy who knows a lot more about this stuff than any of us.

Here is his qualifications.

- 11 years of SUCCESSFUL autocrossing (read SUCCESSFUL as I hold several class championships)
- NASA East Coast Honda Challenge Competitor (road racing)
- 8 years as an SCCA National Tech Inspector
- 6 Years as an SCCA Safety Steward
- NASA Tech Inspector
- NASA Grid Chief
- NASA Safety Official
- ASE Certified Master Technician
- 8 years of experience with a PREMIERE American Honda tuner where I have assisted in building numerous national champion cars (we have never put x-drilled rotors on any of them)
- I have crewed for World Challenge teams (none have ever used x-drilled rotors)


If you guys feel your DRILLED rotors are better, great. To those of you who actually understand what has been posted, you are welcome.

[SilverY2KCivic]

Understanding it or not, the truth is out there with how they perform for each individual person that uses them, no rockect science there, just common sense, apparently that's below you though.

So I guess you're saying the manufactures that DESIGN and ENGINEER this stuff such as Baer, Brembo or Wilwood don't know what they are doing if they use slotted and\or drilled rotors for their performance systems? Maybe you should call up and talk to these companies and find out rather than relying on the info from an engineer that doesn't design nor fully know the COMPLETE engineering intellect on brake systems and why companies and car manufactures use what they do for brake systems.

[SkylineUSA]

If you get your information from the manufactures, I see your problem right there

Try to find the information through research, not what some guy is trying to sell you, geez.

Like I said before, I will never have cross-drilled rotors on my car. I will leave it at that, Good Day.

[SilverY2KCivic]

Originally posted by SkylineUSA
Like I said before, I will never have cross-drilled rotors on my car. I will leave it at that, Good Day.

Fair enough, just the same I'm not going to junk my Power Slots for some blanks.

[micheal]

good article. thank you.

[SkylineUSA]

For the most part, what I was getting at. X-drilled are fine for street use with light cars, they do help to a point, but you better keep an eye on them.

I just installed some Apexi floating slots, they help drastically. I'll post some pics if you want to see them.

[SilverY2KCivic]

Originally posted by SkylineUSA
For the most part, what I was getting at. X-drilled are fine for street use with light cars, they do help to a point, but you better keep an eye on them.

I just installed some Apexi floating slots, they help drastically. I'll post some pics if you want to see them.

What the heck are those? I'm interested to see.

Going back to the original topic discussion, what it comes down to is form over function. Take a look at a 360 Modena. The standard street version comes with x-drilled rotors (for show Ferrari admits) whilest the 360 Modena Challenge racing version that's also street legal, but comes prepped for club style and track racing, comes equipped with slotted rotors instead (function). So in all, only slotted or blanks are meant for performance, x-drilled is just for looks.

I ask this though since I see it both ways, for slotted rotors, is it better for the slots to go WITH or AGAINST the caliper as far as the direction of them... Mine are installed with them going WITH the caliper as Power Slot has them labeled to be installed as. But what would swapping them from left to right so the slots go AGAINST the caliper do to or for performance?

[Moppie]

Ladies please!


Your both right and your both wrong.

SkylineUSA is spot on right with the physics, a vented disc with a smooth face will provide greater braking force than an equivlant disc that has been cross drilled or slotted simply because it has more surface area.
Its something that any automotive enginer knows, and its something that been used in car design since the invention of the brake disc and pad.
Take a look at the average car on the street and notice that almost all of them will have only vented discs. No fancy holes or slots.
The cry of "its done to save money" dosnt hold up as an excuse either.
Brakes on the average road car are designed to work once in an emergancy, and the disc that will provide the most stopping force in such a situation is vented only. This means a smaller disc can be used to save money and weight. Not the otherway around.


Putting slots or holes in a disc compromises braking power in the name of reducing brake fade. Its been proven to work, but at the cost of reduced brakeing force, and as a result on every race car I have ever seen or worked on that has been fitted with slotted or drilled discs a larger size disc has also been fitted to compensate (as well as add to an increase in braking performance)
On a road car its important that when fitting aftermarket slotted or drilled rotors its important that the size of the disc is also increaced to increase the swept area to compensate for the area lost to the holes.
If you dont then you risk decreasing braking power.
Any increase you may feel will be either psychological, or due to fitting better pads at the same time.



Now take a look at the brakes on an Australian touring car, or a F1 car (if you can see them) they are only vented, no holes or slots.
There is a very good reason for this, brake pad manufactors now claim to be able to make pads that produce close to zero gas as the material burns up which means slots and holes are simply not needed to vent it off.
On race cars the drilled and slotted rotor is dying, its possible the slotted design has some benefits, in that its able to remove any parts of pad that may break off despite what the manufactor may claim, and simply because after over 50 years of use its hard to change peoples minds on the matter. A lot of people building race cars are not prepared to try totaly new things untill someone else has proven it works, you can see how that makes it hard for new ideas to be incorperated.


On a road car running street pads its hard to say whether the brake pad manufacors claims of no more gas build up are true or not.
Quite simply a road pad needs to be able to heat up quickly and provide a friendly to use feel, and not destroy discs the way a race pad will.
This means useing quite differnt compounds which will compromise the pads antifad ablities.
If you want to run full race pads on your road car then be my guest, but dont complian when you need a new set of discs every 6 months.
This means that provided you increase the disc size to compensate useing slotted or drilled discs may over some advantage if your drive regulary in such a manner that fade from gas build up is a problem.
But lets be honest, I doubt any member drives that hard on a regular basis, and if you do then I doubt you'll live or own a car long enough to worry about it.
If your into weekend track racing, then simply buy a set of full race pads and fit them at the track.



Now as for the Argument of "but Porsche and Ferrari use drilled slotted discs"
Well so what? All it shows is they have done thier marketing home work, dont believe the pad manufactors cliams and are reluctant to do something differnt.
I know a lot of exotic car owners, and I think you would be amazed at how ignorant a majority of them are when it comes to how thier car works. Many of them buy the car for the image it portriats, and as far as they are concerned if it has slotted or cross drilled discs then it must be fast. That is the extent of thier reasoning, and manufactors like Porsche and Ferrari know this. Porshce has been pushing the same car design on people for 70 years, you cant cliam they dont know marketing.
Its quite pluasible they dont totaly believe the pad manufactors claims, when your selling one of the worlds best performance cars you dont want to risk that performance because the owner fits aftermarket pads.
Quite simply they can easily afford to fit larger discs that are drilled or slotted, and not face any compromises.





So both of you ladies are right, you both have quite valid arguments, but you both seem to miss each others points.
After all the above is nothing more than a summary of what you've both said with a few extra points of my own.





Now as for whats better for your road car?

Well quite simply the single biggest change you can make to improve your braking performance is a quality set of aftermarket performance pads.
Fitting a set of slotted or drilled discs that are the same size as your orginals will have little to no effect on your braking performance, as most of the inefficancy in factory set up comes from the pads and not the discs.
Slotted or drilled discs the same size as the orginals have no use except on a show car.
Once you've fitted better pads then if you still want better brakes you should start looking at aftermarket discs and calipers. Bigger of course than the stock size. And when choosing decied what sort of pads your going to use with them.
But dont bother fitting anything that is only the same size as your orginal discs.

[SkylineUSA]

SkylineUSA is spot on right with the physics, a vented disc with a smooth face will provide greater braking force than an equivlant disc that has been cross drilled or slotted simply because it has more surface area.

You might want to rethink that statement. It has nothing at all to do with surface area. Its the mass of the rotor and its ability to dissapate heat, not surface area.

I do not see in any part of your statement that proves what I have been saying is wrong, or missed the point?

I will admit, that everything else you have written is very true.

As for the direction of the slots, ?

I'll post some pics when I get a chance.

[SkylineUSA]

Here is a pic, installed.

Basically, a 2 piece or floating rotor consists of the hat, and the disk. The hat is aluminium, and is mounted onto the disk by 10 bolts. The aluminium acts as a better heat sink, and it makes the rotor much lighter than the normal rotor. 5lbs lighter each, this is sprung weight of course which is a big bonus. Where the hat mounts to the disk is where the play is, this is to allow for expansion of the disk, because the disk primary function is to take the moving energy of the car and convert it into kinetic energy. And what happens Ladies (as Moppie so elegantly stated in his previous post) when this action takes place, that right it creates heat. Floating rotors will less likely warp, because of the way they are engineered.

I will say this, it did help in dropping the stopping distance dramatically going to the floating disks, not sure if its because of the slots or the increase ability of the rotor to dissipate heat, but you can tell a difference. I would be willing to bet its the heat dissipation ability. With holes in a rotor, the rotor will heat up faster, because of the loss of mass. Yes, it does have a little better ability to dissipate heat, but there will be a point depending on its load, were the x-drilled rotor will fail.

If you guys do look for some, the float, or play should not be more than .2mm. Since I am in England they use the metric system, if you convert that to our standard system, I believe it would be close to same distance that Robert Horry's game winning shot was off in game 5

I am willing to learn

[SilverY2KCivic]

Geez, I shoulda known that! :o A floating rotor is basically a 2-piece rotor where the hat is sperate from the actual disk itself. Now when bolting the two together, doesn't the hat need to also be wire tied to the disk incase the two ever happen to seperate? I remember reading an article in SCC magazine way back where on a project '92 Civic hatchback, they fitted it with a set of Wilwood big brake kit up front, but since the rotors were the floating style, they had to wire tie sime metal wire around each bolt for safety purposes or something to that affect.

[SkylineUSA]

I read that article, you are suppose to safety wire them. Are mine, no. I did use Loc-tite. The way the Apex 2 piece rotors are made, you would have to have all 10 bolts fall out, before they would become unsafe. I would hope I would notice something before then