Cross drilled rotors, better or not?

Its a good read.

Some of you might have read it already, but some have not.

www.altimas.net/forum/showthread.php?s=&threadid=32327&pagenumber=1

I have brembo drilled+slotted rotors on my car and I TOTALLY DISAGREE with what the maxima guy said about them.

1. They were too large in diameter (supposed to have been stock replacement), had to have the calipers ground to accomodate (I needed brakes so I couldnt wait for a new set).
2. They chatter under moderate to hard braking (sounds like the slots hitting the edge of the pads). I know its not the abs
3. Doesnt work well with my abs.
4. Less brake surface area = less stopping power.
5. Once they get surface rust, they stop looking good.

Fliquer,

Did you read the whole thread? There is better information later on.

I like my AEMs. 30k miles, no probs. Better stopping than stock.

DemonicAccord,

What did you think of the thread?

whatever fancy boy, you're right I'm wrong. feel better? sheesh

Yes, your right, physics is hearsay and conjecture. Glad to have enlightened you.

I did not post it here to start an argument, it was to educate the guys they don't know.

the aem's dont really count in that regard, b/c they're not factory sized..

larger swept area means better braking...

it would be true even if aem used a solid rotor...

and they are switching to mostly slotted rotors...

most motorcycles (all really)... use drilled rotors...

why no slots there?

So the best rotors are huge in diameter to disperse heat throughout the rotor, thick for strength, and have holes to vent gas and slots to clean them?

After doing some research into which is better... I ended up with True-Stop (a little over $20 something apeice) front roters from NAPA for mine... hehehe

This was from reading posts by peeps that "actually" design or "test" rotors, pads. Sure if your going to be doing alot of track racing, then you want to step-up to the drilled/slotted ect.... However, with street and occasional track use. Then going with Tru-Stops, ect... will work just fine, and save you a bunch of money. That could be used on other performance gains.

If your going for show tho, thats a different story...

Pnoi Q, and 88_SC_CRX_Si,

Did you guys read, by chance, the link I posted? I am thinking, no.

Slotted and Cross-Drilled rotors actually do decrease your stopping power but it also keeps the rotors cooler to prevent Warping of the rotor. You have to find out if it is worth it to you to get slotted and (or) cross-drilled rotors.

Yeah actually I did... The huge rotor is used to dissipate the heat and prevent cracking, that's what the one guy was saying. Then there were those who were fighting for the slots which said got rid of brake dust and such. Then there were those rotors that were thick in diameter, which gave the rotor more strength. AND FINALLY the holes/crossdrilled vented all the gas.
Soooooo... My conclusion is that a compromised rotor would be the best of all the worlds.
Big diameter=Less Cracking
Slots=Cleaner Brakes
Thick=Stronger Rotor
Crossdrilled=Vent Gas
Although having the slots may need more of a stopping distance compared to that of just a large diameter, it still will stop better than stock, and it still will be cleaner than if I had no slots, which in turn would look better. I forgot why venting the gas was important though.

Brake Fade for venting the gas;)

Originally posted by Pnoi Q
Yeah actually I did... The huge rotor is used to dissipate the heat and prevent cracking, that's what the one guy was saying. Then there were those who were fighting for the slots which said got rid of brake dust and such. Then there were those rotors that were thick in diameter, which gave the rotor more strength. AND FINALLY the holes/crossdrilled vented all the gas.
Soooooo... My conclusion is that a compromised rotor would be the best of all the worlds.
Big diameter=Less Cracking
Slots=Cleaner Brakes
Thick=Stronger Rotor
Crossdrilled=Vent Gas
Although having the slots may need more of a stopping distance compared to that of just a large diameter, it still will stop better than stock, and it still will be cleaner than if I had no slots, which in turn would look better. I forgot why venting the gas was important though.

Well put Well put *claps*

So, you read the whole post? I guess looks count for a lot, at least your some what better informed.


True. Crossdrilled rotors were developed for racing in the 50s when brakes pads sucked. They would off-gas at relatively low temperatures. The holes gave the gas somewhere to go. If not, it would get trapped between the rotor/pad and the pad would not make contact with the rotor. That is called "fade". Modern brake pads do not do this. True, if you take a street pad to the race track and exceed it's operating temperature, you can get it to fade. But I challenge you to get a Hawk Blue, or Porterfield R4 brake pad or other dedicated racing pad to fade. Ever. Simply, crossdrilled rotors fix a problem that no longer exists.


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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).
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Surface area dissipates heat. The amount of surface you create from drilling holes is almost insignificant compared to the initial surface area of a standard OE vented. In additionx-drilled rotors will reach higher peak temperature because you are removing metal from the rotor. The metal is what absorbs the heat. Plus, you are reducing pad/surface interface. Tell me again why this is a good idea?


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I ask any local non-believers to take a ride in my car, I would be happy to allow them to drive it just so they can tell you about the brakes
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I do not doubt your car stop well. Obviously, if you replace busted/worn out OE parts with new x-drilled parts, of course it's going to stop better. What I do doubt is that it stops better than regular new OE-style non-drilled/slotted rotors. I *garuntee* it does not.

Don't believe me? Will you believe an engineer that designs automotive braking systems?

Originally posted by SkylineUSA
[B]So, you read the whole post? I guess looks count for a lot, at least your some what better informed.

I'm still a noob, so bear with me. :D

Yeah it's true that looks count for alot. Especially if your aspiring to be winner or at least runner up at HIN; unfortunately, for me at least, I can't focus solely on looks because my brakes actually need to stop (the car I plan on entering into HIN is also my daily driver) That's why I wanted the best of every world.

But from what you've given me crossdrilled rotors aren't required anymore. What about large diameter rotors with slots? Maybe I'll end up just getting high quality calipers/pads and large rotors. Brakes are actually my priority mod right now; so any advice will be taken gratefully.

Pnoi Q,

You might be a noobie, but at least you get it, unlike some others that cannot understand physics.

Slots are OK, if you need the so called "bling, bling" effect, but will tell you this, I would never put crossdrilled brakes on my GTR.

Its up to you, what you put on your car. If you want guidance from me, my brakes will have the most mass as possible, with cooling ducts, racing brake fluid, and some damn good pads.

I do not know what Hondas have for aftermarket brake systems, but the set of brakes for my car will run about $3k.

What brake kit are you using?

Right now I am running the stock ones, but I have my eye on some APs, or maybe some Brembos.

I have a few more months to look into it. I never just take one source for my information and think thats gospel, so I am still doing research.

Originally posted by SkylineUSA
Pnoi Q, and 88_SC_CRX_Si,

Did you guys read, by chance, the link I posted? I am thinking, no.

Yes, I did read the post you posted, why do you think I posted on this one... It does not have any mention from PEEPS, that ACTUALLY do work in the industry. Unless I missed something there... among all the flamming and so forth. hehehehe

Sure, I can install brand new rotors/pads... What good is that, if I do not have the system flushed along with it... It depends on the overall condition of the system. Rather then just a couple of components, that will deceide how well things will work.

Anyway, to each his own....

If you do any brake work I would hope you would flush the system, that goes without saying. You are right, to each his own.

Sure if your going to be doing alot of track racing, then you want to step-up to the drilled/slotted ect :confused: You might want to do a little more research:)

It's whatever.... hehehe

Ok. I just put some Ractive cross drilled and sloted rotors on my car. I put on new OEM pads as well. I can stop on a dime. I noticed imeadeatly an improvement in braking. Say what you will, but if you didnt notice they are on all the stock cars and indy cars... Why?

Originally posted by seth 90DX/ZC
Ok. I just put some Ractive cross drilled and sloted rotors on my car. I put on new OEM pads as well. I can stop on a dime. I noticed imeadeatly an improvement in braking. Say what you will, but if you didnt notice they are on all the stock cars and indy cars... Why?

Also why would they come stock on Porche TT's and pretty much all other porche's and high end Sports Cars? Why is it that the Porche has one of the best braking distances? That doesn't make since to me because there are engineers that design those.

Originally posted by SkylineUSA
Pnoi Q,

You might be a noobie, but at least you get it, unlike some others that cannot understand physics.

Slots are OK, if you need the so called "bling, bling" effect, but will tell you this, I would never put crossdrilled brakes on my GTR.

Its up to you, what you put on your car. If you want guidance from me, my brakes will have the most mass as possible, with cooling ducts, racing brake fluid, and some damn good pads.

I do not know what Hondas have for aftermarket brake systems, but the set of brakes for my car will run about $3k.

If it's just "bling bling" like you say, then why do the new S-class Benz's come STANDARD with x-drilled rotors? Why do Porsche's come with x-drilled rotors? I could go on with other cars that come from the factory with them. If they weren't nessacery or made a differance on brake systems anymore, then companies wouldn't be putting them on cars. A manufacture wouldn't put a part like that as STANDARD equipment on a car just for show. Think before you post. :rolleyes:

I'll give you that you gotta be going some pretty fast speeds for the drill holes or slots to make a differance, but they can and DO make a differance. But I'd say above all is on what pads you're using, what kind of lines, and what fluid is running the system.
On my Civic I'm running Power Slot rotors, and AEM/Nissin OE spec hi-pro pads on the front (not much aftermarket help for rear drums short of swapping out for rear discs) and then I'm gonna get a complete brake system flush soon here, and replaced with some Motul DOT4 racing fluid, and then the lines changed out for some Goodridge S/S lines.

The plethora of cars you mentioned are NOT X-DRILLED, they are cast with the holes in them, you might want tothink before you post.:p

You can lead a horse to water, but you can not make him drink, most of you guys are going to die from dehydration.:D

If you guys swear by holes being drilled into your rotors, so be it. The information is out there.

I give, Peace.

Originally posted by SkylineUSA
The plethora of cars you mentioned are NOT X-DRILLED, they are cast with the holes in them, you might want tothink before you post.:p

You can lead a horse to water, but you can not make him drink, most of you guys are going to die from dehydration.:D

If you guys swear by holes being drilled into your rotors, so be it. The information is out there.

I give, Peace.

I never said my brakes had any holes in them, now did I? ;)

And upp I dunno what rock you're living under but EVERY car i mentioned in my post has or comes with DRILLED rotors of some sort whether it by true cross drilled or POS drilled after the fact. And I HIGHLY doubt the $3k Brembo system on a Porsche isn't a TRUE x-drilled system (that's what the holes are called no matter how they are put into them). Think about it, what other car has an option of ceramic brake rotors and a super high performance braking system?

Anywho, I was thinking before I posted, you basically stated that holey discs are pointless, I'm showing you that they aren't, if manufactures like MBZ or Porsche doesn't think they are, they wouldn't spend the extra to put them on their cars. And yes, I already knew those cars come with pre-cast drill type holes, rather than ignorantly drilling the holes after the fact.

I know I certainly wouldn't die in that desert. :D

Originally posted by SkylineUSA
True. Crossdrilled rotors were developed for racing in the 50s when brakes pads sucked.

Are yopu out of your mind? The brake pads in the 50's-60's-70's were espestos! They are WAY better than the shit pads we wipe our brakes with now dude! The only reason we dont use the better pads now is becasue of a bunch of hippie as inviro's fuckin up the scene once again. Now they fuck up our emissions shit with dyno rollers.

Originally posted by SilverY2KCivic


I never said my brakes had any holes in them, now did I? ;)

And upp I dunno what rock you're living under but EVERY car i mentioned in my post has or comes with DRILLED rotors of some sort whether it by true cross drilled or POS drilled after the fact. And I HIGHLY doubt the $3k Brembo system on a Porsche isn't a TRUE x-drilled system (that's what the holes are called no matter how they are put into them). Think about it, what other car has an option of ceramic brake rotors and a super high performance braking system?

Anywho, I was thinking before I posted, you basically stated that holey discs are pointless, I'm showing you that they aren't, if manufactures like MBZ or Porsche doesn't think they are, they wouldn't spend the extra to put them on their cars. And yes, I already knew those cars come with pre-cast drill type holes, rather than ignorantly drilling the holes after the fact.

I know I certainly wouldn't die in that desert. :D

Ok lets clarify for all the suhie's out there (Inside joke ;) The X-drilled part wether it be drilled or casted (it doesent mater its the same fucking thing) is there to cool the discs, this alows MORE braking. Sloted rotors arent just for show, if you actualy read about this shit you would know there is a gas that builds up between the pads and the rotor which pushes the pads off the rotor until it blows out under presure and your wheels lock up. I have noticed its ALOT harder to lock up my wheels, I realy have to slam on the brakes goin 100+ mph. Basicaly I could slam your face into my window hard enough to break the window stoping from 100 if you werent wearing your seat belt without skiding or locking up my wheels. So the slots are there to relieve gas under presure.

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?

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).


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

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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).
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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.

:)

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. :rolleyes:

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.

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.

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

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.

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. ;)

good article. thank you.

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.

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. :cool:

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?

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 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.

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;)

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.

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;)

Originally posted by 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;)

LOL, yeah, I mean it would take A LOT for just one or two let alone all 10 per hat to fall out. :p But the Loc-tite should be just as well as the safety wires.

This pic below is what I was talking about with the reversing of the rotors when slotted. The rotors on the car in the pic are put on so the slots turn AGAINST the caliper, so that the outside edge of the slot reaches the caliper first verses how you have your rotors put on, which is also how mine are on right now. An advantages/disadvantages to having the slots in this direction?

Originally posted by SkylineUSA
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 didnt say anything about heat disapation. A solid disc exposes a greater surface area to the pad than a drilled or slotted disc, and so theres more friction and greater braking force, but of course at the expense of more heat.

So,

Where was I wrong in what I posted?

Just to stick my nose up in this, both are right. You DO need something that will disipate heat better and quicker (larger rotor) but you also need/want something that'll let you slow down quicker (solid surface area). Thing is, I really have yet to see a big brake upgrade kit that offers say like "13 solid blank rotors. Look at all the popular big brake kits from Baer, Wilwood, AEM, Brembo, ALL come with slotted if not x-drilled rotors. Defeats the whole purpose of a larger brake, doesn't it?

Let me bump something else into the equasion here, what does THIS kind of brake system do for a car in terms of braking ability? :p

Of course the surface area will be a player in the scheme of things, but that is not what stops your car.

Those brakes, where did you find those, or better question who in the hell would make them:D

Originally posted by SkylineUSA
Of course the surface area will be a player in the scheme of things, but that is not what stops your car.

Those brakes, where did you find those, or better question who in the hell would make them:D

LOL, I thought those might perk a comment or two. I company called "The Brake Man (http://www.thebrakeman.com/)" makes them. They are called buttercup rotors for their distinct shape of a buttercup flower. These are definitely show of course, and when I first saw them on a car in Super Street I think it was, I didn't think you could actually drive with them, but apparently you can.

I didn't think you could actually drive with them, but apparently you can. Ya, you can drive fine with them, you just can't stop.

Originally posted by SkylineUSA
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.

Hello,

Great thread..

You're partially right - a xdrilled rotor may have less mass than a blank while at the same time its surface area measured on all axis still being roughly the same due to the holes increasing the surface area on the z-axis (assuming you are looking at the hat of the rotor).
However, decreased mass will result in a lesser ability to distribute heat energy thoughout the rotor, thus making it less "efficient" at dissipating heat, which results in increased rotor/pad temperature and reduced breaking performance as well as risking structural integrity - it all goes downhill from there..
When moppie refered to "surface area," I am assuming that he meant the surface area on the x and y axis - the axis that matters the most. The larger the surface area on the x and y axis, the more friction can be generated between the surface of the rotor and the brake pad, and greater enegry transfer (stopping power) can be obtained. A smooth surface will also help insure that more of the pad surface area is in contact with the rotor.
As moppie mentioned, the only time xdrilled or slotted rotors will _really_ make a difference is if you increase the size of the rotor to compensate for the removed surface area on the x and y axis of the rotor. BOTH for heat distribution AND breaking power.
Some may argue that because some surface area on the xy axis is removed, that there will be less friction, and therefore less energy transfer in the form of heat, which in turn compensates for the lesser mass of the rotor. In either case, you are making your braking system less efficient at doing what it was designed to do.

I'm with moppie on this one.. Unless you're upgrading to bigger rotors, xdrilled or slotted rotors are a waste of money if your goal is decreased stopping distance. The best upgrade you can do on a stock-sized rotor is to upgrade your brake bads.


As for the direction of slotted rotors, they should flow away from the caliper. In the same fashion that the vents in the middle of the rotor create a centripidal fan which sucks air in from the middle "hat" of the rotor and pushes it out the sides, you want the slots to do the same.

"Your milage may vary.."

tarmac165,

Very well said, and I totally agree, in theory:p





When moppie refered to "surface area," I am assuming that he meant the surface area on the x and y axis - the axis that matters the most. The larger the surface area on the x and y axis, the more friction can be generated between the surface of the rotor and the brake pad, and greater enegry transfer (stopping power) can be obtained. A smooth surface will also help insure that more of the pad surface area is in contact with the rotor.
Moppie said that crossed drilled had less surface area, but you mentioned it increases surface area (which it does), how can the cross drilled surface areas of the holes creat more friction, when they are not in contact with the pad?

As for the way the slots should face, I really do not think it matters. But, the way explained it, the pic that SilverY2KCivic posted, you are saying is correct?

My hole point was more mass for the rotors, I guess I did not explain myself that well, sorry guys.

Like I said, I totally agree with your post, tarmac165.

Originally posted by SkylineUSA
Moppie said that crossed drilled had less surface area, but you mentioned it increases surface area (which it does), how can the cross drilled surface areas of the holes creat more friction, when they are not in contact with the pad?


SkylineUSA, I believe you may have misunderstood me.

Cross drilling may increase the OVERALL surface area, but it does in fact decrease the surface area in contact with thre brake pad. Again, when moppie made his statement, I am assuming he was refering to the surface area in contact with the brake pad, and as I (and moppie) stated before, crossdrilling or slotting your rotor will reduce its ability to do its job unless compensated by increasing the diameter of the rotor to increase the surface area in contact with the pad (big brakes upgrade).

However, as you said, surface area is not the only variable, MASS is very important as well.. It takes much more energy to heat a large item than it does to heat a small item... With any good heatsink, the larger the surface area, the more efficiently it can dissipate heat. While drilling/slotting your rotors will increase the rotors ability to dissipate the heat, it is also of smaller mass and therefore heats-up quicker, and has to store more heat in a smaller space... It's all a tradeoff.. The key is to find the best compromise.

Originally posted by SkylineUSA
As for the way the slots should face, I really do not think it matters. But, the way explained it, the pic that SilverY2KCivic posted, you are saying is correct?

My hole point was more mass for the rotors, I guess I did not explain myself that well, sorry guys.

Like I said, I totally agree with your post, tarmac165.

That particular setup would work great if you were going 100MPH in reverse. :)

It is my belief that the rotor installation illustrated in the picture posted by SilverY2KCivic is incorrect and may be for show purposes only.

Correct installation is as follows:
http://www.kllr13b.com/images/ap5200.jpg

Although I have never tested a slotted rotor in the "reverse" direction to be able to tell you for sure if it makes a notible difference or not. I can tell you that logic would indicate that there is only one proper way to install sloted rotors. You want the slots in the rotors to begin on the inside and work their way outward with rotation. This is because you want any particles that come off of the pad to be propelled off of the surface outward with rotation, and not inward.


-Alex :cool:

When I read you post, it was 1 am in the morning, and I had a few pints from the local pub too boot. :p

I believe everything you have just posted, is the same thing I have been saying all along.

So, we all agree, that Cross-Drilled rotors really do not help, unless they are physically bigger.


tarmac165,

Thank you for posting the clarification on the slots as well.

Originally posted by tarmac165


Although I have never tested a slotted rotor in the "reverse" direction to be able to tell you for sure if it makes a notible difference or not. I can tell you that logic would indicate that there is only one proper way to install sloted rotors. You want the slots in the rotors to begin on the inside and work their way outward with rotation. This is because you want any particles that come off of the pad to be propelled off of the surface outward with rotation, and not inward.


-Alex :cool:

That's a very excellent point there. But there's gotta be something to reversing their direction. Maybe it's not something to do in street applications, but I have pics (from the June '03 issue of Car & Driver magazine) of SCCA World Challenge road racing cars that use slotted rotors, and they are reversed like in the pic I posted. Maybe when they are used the amount those cars use their brakes, and at the speeds they use them at, maybe reversing has a better effect of the slots than running them in the normal direction that draws the air away from the center of the hat like in the pic you posted.

OK, not having read this theread here's my opinion:

1)cross-drilled helps dissipate heat better, it's proven
2)cross-drilled cracks easier, it's proven
3)if cross drilled correctly (i.e. chafered holes) they will hold up almost as well as solid rotors
4)slotted is ultimately just a compromise

1)cross-drilled helps dissipate heat better, it's proven Really? Please show us.

Of course, if you are talking about the Swiss cheese rotors that Porsche uses, I wonder how much they cost?


For the record, I am in complete agreement with tarmac165, on all subjects:sun: