90ZR1

You are correct, when I said cermaic pads create no brake dust, what I meant was it is much more minimal then most other pads... anyways...

A cross-drilled rotor will provide an escape path for the gasses over the entire life of the rotor. This is especially beneficial as the rotor gets thinner near the end of its usable life.
Well obviously it also depends on the thickness of the rotor to make the surface area. Here, I'll explain what I mean:

Area (let's just do the area of one cross-drilled hole ok?

NON CROSS DRILLED

Area=2(pi)(radius)^2 (the 2 is for each side of the rotor)

CROSS DRILLED

Area=2(pi)(R)(l) (the l is the thickness of the rotor)

Now, to find out where the areas equal each other, let's make the two areas equal:

2(pi)(radius)^2=2(pi)(R)(l)

Cancel out the repeating terms and you come up with r=l

So as long as the rotor is thicker than the radius of the hole, you end up with ultimately more surface area. And note that that radius of the holes is usually very small and while the rotors aren't always really thick, they're thicker 90% of the time, especially considering that cross-drilled brakes are usually aftermarket and therefore thicker.

For the cross drilled equation, note that I only included the rectangle formed by the circumference of the hole (2*pi*radius) multiplied by the rotor's thickness.

And like I said before, the rate of reaction (heat transfer in this case) is dictated by 3 things:

1)Surface area (the more surface area, the quicker something happens). Prove this by putting a drop of water on your counter. Then, put a drop on the other side, but make is cover more area (i.e. spread it out). Which dries first??

2)Temperature (temp. difference in the case of heat transfer). Cross drilling, slotted or solid rotors don't really make much difference in my argument.

3)Catalyst - not applicable.
And when you think about it, you don't really require tiny holes or overly thick rotors. The radius of one cross-drilled hole is tiny anyways, the rotor needs not be very thick to meet my stated conditions.

And you can compensate for the loss in swept area by increasing the force, like many cross-drilled braking systems do (I'm thinking along the lines of the Brembo Big Red Brakes system). They just add more pistons and more braking force capability.

There, I've explained myself.

And one little tidbit I thought I'd share: I'm not asking you guys to agree with me. I've shown my points and that's all I really have to say, I just think that cross drilling certainly doesn't decrease performance. Like people say, it may not increase (dramatically or whatsoever) braking performance, but you guys seem to speak of it like it's the antichrist.

If it's as useless as all of you say, it wouldn't be used so much. It may not be useful in all respects, but it's certainly better than solid rotors.

90ZR1

Yes and when I was talking about matching rotors and pads, I meant, aggressive pad, weak rotor, or vice versa.

jargan04

iTrader: (1)

90ZR1 why don’t you talk to someone like Louis and Lou Gigliotti about drilled rotors. If you won’t believe Mitch, and track bird who are well respected road racers and know what they are talking about. Then talk to Lou or Louis, since they road race and DO NOT use drilled rotors. I have given up hope on you learning that with today’s pads, the there is no out gassing problems.

93octane

I think that the point is that if you are a hardcore racer, cross drilled are not for you. If you are mainly on the street and want something that looks good and "might" last you longer, go for the cross drilled.

Whatever the case, the rotors look great.

Casper9T9

iTrader: (1)

The surface area of a cylinder is S = 2(pi)r^2 + 2(pi)rh. If you drill holes in it the surface area in contact with the pad decreases. I'm not sure why you would care about the total surface area anyway. The area that maters is where the pad contacts the rotor. I'm sorry, but I don't see how your equation has any relevance.

90ZR1

I agree with koolaid... as well I am done with this thread. Jus drive and keep on

trackbird

iTrader: (4)

The odd thing is, Baer uses a great casting as the basis for their Eradispeeds. If I could get them without the holes/slots, I'd consider running them. They are probably better than the blanks that most (or all) of the other drilled and slotted rotors that are out there. They are still expensive, but they are based on an excellent rotor. Unfortunately, they ruined them by filling them full of holes.

mitchntx

iTrader: (14)

Don't turn it around ...

The ORIGINAL statement was something to the affect that C/D rotors provide better stopping power due to heat dissipation, pad out-gassing and ventilation. And that is just plain an untruth.

Also, it's quite a steep price to pay, unless you KNOW the facts and not manufacturer hype. During the 2K1 Hot Rod Power Tour I asked one of regional sales guys from BAER if the Eradispeeds would hold up under AX and/or road course duty and was told flat out, "No!"

C/D rotors are driveway jewelry and have no POSITIVE affect on stopping the car.

Do they work? Certainly.
Do they help? No.
Are they worse? In some cases, yes.

trackbird

iTrader: (4)

You can, in fact, make them yourself. First, cut some bread to the size of the backing plates. Toast bread on both sides. Add a suitable layer of cream cheese. Install and follow the standard bedding procedure.

This way, when you claim your pads are toast, you really mean it.

sb427f-car

Then what would you suggest running for a quality rotor that won't warp, brake, crack, and does stop the car hella good? Also, why do you see Nextel Cup cars running x-drilled rotors @ Daytona and Talladega? to cut down on weight? What do they run at Martinsville, Bristol, Richmond (short tracks) and then at Michigan, Atlanta, Charolete, Dove (large to intermediate tracks)? I'm curious in all seriousness now. Granted they have huge budgets and only need to make a rotor last for 500 miles but I swear I have seen x-drilled and slotted rotors on those cars during TV shots of practice. Good info btw.

Also, if the holes and slots are cast in (is that what they do in some casses?) doesn't that help to create a less fatiguing in the holes/slots? Can't you add radiuses or chamifers to the holes in this fassion from the mold?

trackbird

iTrader: (4)

Many nascar teams use Wilwood rotors. Many of their "cup" rotors are slotted (often in "odd" patterns). I've not seen drilled rotors on a cup car, but I don't look that often. Many of them use a heavy duty slotted rotor from wilwood or Coleman racing, etc.

As far as the cast in holes. We've been trying to prove that myth (unsuccessfully) on another board. There was even "bounty" money offered for anyone who could find proof. We never did. We had pictures of molds and everything, none of them had provisions to cast holes. As far as we can tell, it's a marketing myth that was started long ago. But, we are still looking for proof.

Brembo OEM rotors are excellent rotors that will handle lots of abuse. If you want a good quality rotor that will stop the car under adverse conditions, those are an excellent choice.

02Z06man

How much were the brakes? I need to get some and put on my vette

mitchntx

iTrader: (14)

You nailed it ... weight, exotic metals and they only have to last 500 miles ...

The short track rotors are hella thick and have 3 seperate ducts of forced air fans running to them.

And on 12/24 hour RR cars, notice how after about 8 hours or so, they are changing brakes?

I am running $25 Wagner rotors from O'Reilly's on my CMC Trans AM after Autozone quit doing lifetime warranty on the Aimcos. On my street car, I have the C5 upgrade and run $18 GM Durastops.

sb427f-car

So...who offers Lifetime warranties on rotors though? I do know that they change brakes about every 8 hours (mainly just pads right?) on the enduros. Remember back a few years ago that the corvette teams were obstinant and didn't bother to change brakes @ Le Manns (I think more to prove a point) than anything. Ok, so you answer my question about casting in x-drill, what about slots? same deal? I know those cup cars use a lot of brake ducks to cool them, (usually one to the caliper, one to the rotor and one on the whole wheel, tire, brake assembly to keep them cool.

EDIT/NOTE: NASCAR doesn't like to many exotic matls used thought.

trackbird

iTrader: (4)

Slots are machined into the rotor face. If they are done right, they will only have a minimal impact on rotor durability (and if the rotor facing is sufficiently thick/strong). So, a heavy duty, carefully slotted rotor can work for racing use. And, they only need 500 miles out of them.

jRaskell

iTrader: (1)

I am still surprised when somebody so adamantly supports cross drilled/slotted rotors as an honest performance upgrade. I know I shouldn't be, but I am.

No offense 90ZR1, but you would have failed the Thermo dynamics class I took in college, and you haven't even touched upon the fluid dynamics aspect of this particular debate yet.

Bottom line, cross drilling provides virtually NO additional cooling because there is virtually NO airflow through those cross drilled holes. What it does do though is decrease the mass of the rotor, thus increasing the rate at which it does heat up.

Cross drilling was NEVER done to increase cooling of the rotors. It was done exclusively to address out gassing of organic and semi-organic pads, a problem that no longer exists with today's performance metallic and ceramic pad technology.

Why do Cross drilled/slotted rotors still exist and sell well today? For two reasons.
1. People still like the way they look on their cars. For a street vehicle, a good crossdrilled/slotted rotor doesn't represent a significant risk to braking ability, so they will serve perfectly fine on a street/show car.
2. Simple ignorance. Yes, ignorance is still alive and flourishing in our society today, and yes, businesses are still taking advantage of it, something they've been doing for all of recorded history (and probably well before recorded history)

I don't think anybody is speaking of it as the anti-christ of braking here either.

90ZR1

What I'm basically trying to get across is that they're better over a period of hard braking, but they definitely won't decrease your braking distance.
And my example only took into account the surface area of one hole. Over one hole, the surface area grows so long as the conditions are met. If one hole creates more surface area, multiple holes over multiple discs, well, I figured you guys could get that one on your own
And when you think about it, you don't really require tiny holes or overly thick rotors. The radius of one cross-drilled hole is tiny anyways, the rotor needs not be very thick to meet my stated conditions.
Drilling was/is for cooling. Chamfering the hole entrance helps venting and lightens the rotor at the penalty of further reducing contact surface for braking. Casting the holes allows for simultaneous results of chamfering and surface-stress relief by having the surface of the holes the same surface as the rotor interior. Also, chamfering reduces pad consumption slightly, but here at a penalty of less pad cleaning. Chamfering also has the brake dust build more at the trailing edge of the hole and can be seen to polish it's own bird-eye chamfer.
And as far not passing your thermodynamics class in college...

Again I'm not asking anyone to agree with me, just telling you how I see it, I am done replying on this thread so enjoy!

BrandonSS

iTrader: (1)

Eh... true, but without getting into the serious math of it. The drilled cylinder will actually INCREASE the mass surface area. Increasing surface area increases the ability to dissipate heat at a higher rate. Yes, less mass will allow the metal to heat up faster. What am I talking about?

Example... holes that are .1" across and .3" deep(not close to real just example)

Surface area of original metal (inside and outside contact surface "undrilled holes") = 2pir^2
Surface area of the new cylinder (non chamfered drilled hole sides) = (2pir)*h

SA of original= .0314 sq. in. (picture as outling where we are drilling)
SA of new= .0942 sq. in.

A gain of roughly 66.666% surface area, or .0628 sq. in.

So if a blank 13" rotor has 296.73 sq. in. of sweep surface area (front/back pad sweep)
the drilled rotor with 72 holes in each half has (total of 144 inside and out pieces) .... 305.7732 square inches of surface area which is 9.0432 MORE sq. in. than it had before.

Without drawing out a book of heat transfer, convection (or radiation)... (which i dont remember all of that crap.. maybe one of you do and can formulate this all.... ) I am just showing that the drilled rotors have more surface area to which air can pass (yes the holes will have a turbulance of moving air and more so with the veins of the rotor venting while moving) and dissipate the heat. I am not saying heating is greater than the dissipation rate or that the dissipation rate will be greater than the heating.

Hell, this was probably covered and I may have skimmed over it!?

Not war'ing just looking for mathematical answers now.

I love you guys

RICKY00WS6

iTrader: (1)

I'm no expert, but when my rotors warped I spent the money on eradispeeds 2 years ago. Very happy with the look and performance.

lsx24

iTrader: (45)

Lemans and endurance racing has interesting tech coverage on brakes each year. Next year they are going to have temp readouts per lap and updated graphs of brake pressure and position.

Usually each year of course the occational glimpse of brakes glowing. In fact several cars had glowing rotors, and iirc that happens when temps are over 1200* or so, even with cooling. The audacidy of the tv guys is amusing though, I remember one saying they allow the rotors to become hot enough to glow because it helps race pad friction...I believe they don't run cross drilled during enduros because of the mass, there is just not enough cooling added to justify the reduction in absorbing iron.

I have to say this is a hugly debatable topic for open trackers though. Why do you believe Porsche still runs cross drilled rotors? There must be large amounts of seepage from club racers to Porsche feedback, and I don't know how many club racers have switched to solid rotors...If they are prone to cracking, then they would have some serious problems, no? On the other hand, I firmly believe cracked Porsche rotors are a result of abuse, or alternatively, a lack of cooling. If you have proper cooling ducts and pads designed for the style of driving, then I would assume the chances of rotor damage goes down exponentially. When you sense the rotor/pad combination is getting mushy or fading, you would want to adjust pressure accordingly.

For the casual open tracker, this may not be an issue. I have to say for a serious lapper, there are not many issues that are more important. The last thing you want to do is have to focus on brakes hauling the car down from a buck twenty (!), se la vi.

When I was in Phoenix last year, I spoke to the owner of Bear Brakes. He was working on his kit car at the time, and I noticed he had the GT kit on there, not the 4piston Alcon setup I know he could easily put on. Thing is, he open tracks the car quite often, and since there are brake ducts working in his favor that he custom fabbed, he never had the need to install anything bigger. Of course I told him he was crazy for not running his own 4 piston system, which I'm sure he was able to afford, and he could probably swap them out pretty easily.