trackbird

iTrader: (4)

Ok, a few things.

You will increase surface area by drilling holes. However, the airflow through those holes seems to be "minimal". Meaning they seem to just create hot "pockets" of air. I'm sure there is some additional cooling from the additional surface area, but any positives do not seem to offset the negatives.

The negatives (for lack of a better term) have to do with pad temp ranges.

Meaning this. The rotor with holes in it will heat up faster and to a higher temperature. The problem is that brake pads operate in a specific range. So, it is important to try to minimize the temperature range that the pads must operate in. So, if you use a drilled rotor that is light in weight, the peak rotor temps will be higher than the peak temps on a heavier rotor (more mass to absorb heat). Say the top temp reached by a solid rotor in this application is 1400 degrees. We have pads that work from 250-1400 degrees available today. Now, use a lighter rotor (drilled or just a thin casting, could be either one) and the peak temps may be 1550 degrees. The problem is, we're beyond our upper temp limits. Even if they did cool off faster, we still have the peak temp issue to deal with. The other problem is that you will see peak temps when you are using the brakes the hardest (and need them the most), not a good time to over heat your brake pads and see a brake fade condition. So, one of the issues is that the drilled rotors will operate in a wider temp range and will cause us to need a pad with higher and higher maximum working temps. This will cause us to suffer during any low temp parts of the track (if you brake from 160-20 mph and then have a long straight and a car with effective brake cooling, you may cool the brakes enough to have an issue when you need them next. So, we are better off to minimize the temp range by using heavy rotors (heavy enough).

Now, eradispeeds are fairly heavy rotors (even drilled), the problem is drilled rotors still have cracking issues. They do, if you run them hard enough, they will crack. And, Mitch already stated that they are not suitable for track use (per the Baer rep he spoke to).

And, we've not yet been able to prove that rotors with cast holes actually exist, but we've been trying. So far it appears to be a myth.

Anyway, I'm rather tired and hoping that this all actually makes sense (I'm too tired to proof read it, I'll edit it tomorrow if I find a problem).

I'm out for the evening.

lsx24

iTrader: (45)

I have a question about the rotor area, not the cooling or diameter. More specifically the number of grams and the pad area.

This is somewhat perplexing, now regarding the surface area of a rotor and the amount of heat able to be stored in different kinds of metals. If I understand correctly it means that a drilled rotor has more surface area, it has more grams of iron and may or may not weight proportional to the amount of holes, because of the math required to calculate the volume of a cylender. So the more surface area the more amount of solid is able to transfer heat. When you talk about cooling I believe that is more pertinant to the size of rotor including the holes, not necessarily the amount of holes or not including the holes.

However when you say it has more mass, how is that possible? Wouldn't you have to look at how much mass is required for ok braking, instead of how the rotor is cooled? Basically what I'm wondering is, how can the mass of a rotor go up when it's drilled, this doesn't make any sense at all. Is it possible there is a non direct correlation between the area of the metal and the mass of the metal?

trackbird

iTrader: (4)

In the case of eradispeeds, they seem to use a thicker rotor facing which allows them to "make weight". The problem is, this reduces the surface area (by making the veins thinner) in the center of the rotor where the cooling air actually cools the rotor. So, you can use a thicker casting, drill holes in it and remain as heavy as a thinner casting that is not drilled. However, you will somewhat restrict cooling flow through the center of the rotor (where the rotor pumps air to do the actual cooling). This can be good and bad. The good news is that a heavier rotor will heat up less (making the same 150-20mph stop) than a lighter rotor (the effect of cooling is minimal during brake application, there is some cooling, but for the sake of the discussion, we'll assume it to be minimal). So, the peak temp will be lower, however, the restricted cooling passages in the center of that rotor will cause it to cool at a slower rate than a rotor with more cooling vein surface area. Eventually, you could run into a "heat soak" problem with enough hard use (there are many variables that would have an effect on this situation making it difficult to predict exactly at what level this may occur).

Again, for mild street use, it's not an issue. We are really discussing the "hard core" race aspects of drilled rotors at this point.

Louis

iTrader: (7)

Wow! Where do I start? Or Do I?

Lemans teams rarely change brakes nowadays. After the BMW team went 24 hours with no brake change, and the super fast Toyota team got beat because they DID have to change brakes, Everyone opts for no brake change strategy.

Thats all Carbon/carbon stuff, that has not the slightest bearing on what we do with Steel rotors and good old fashioned brake pads.

Cup cars at the super speedways use non- ventilated discs that look like a piece of swiss cheese. They do that for weight, nothing more. When you are flat-footed 100% of the track, why invest all that weight in brakes?

Martinsville is a different story.

trackbird

iTrader: (4)

Thanks Louis. I forgot about the super speedway rotors, I was discussing the "real brakes" they use for short track/road course.

HPP

Is there a way to compromise on the weight vs heat issue?

Dealing with heat is obviosuly desired, but isn't reducing unsprung weight and rolling mass desired as well (for accel, cornering, and even decel)?

What about those carbon-ceramic rotors, do they work for the street? I heard on Top Gear that the Enzo has carbon-ceramic brakes that supposedly work cold, whereas previous iterations of the technology hadn't.

lsx24

iTrader: (45)

Well yes it makes sense that there is a variation in cooling. A stock rotor does not move the same amount of air as aftermarket, since they were just not designed to do so.

For performance rotors, the middle or meat part of a rotor is where a large chunk of the mass sits. This is where the cooling fins are built. Since rotors are directional, as they spin they create a venturi effect sucking air from the front of the rotor and spinning it around. There will be some debate about how much cooling is increased with ducts (and it makes more of a difference with weak rotors) but that will be along the lines of another dimension of physics if you visualize that aspect.

However, what still is mind boggling, is the width to mass ratio. Most passenger car rotors are approx an inch thick, or less. Most racing or performance rotors (ie, porsche or moveit) are approx 1.25 in thick and more. Thing is, without this added thickness, there would be no offset advantage of a drilled rotor. There in fact would be less mass if it was not padded with thickness. That is not to say there's a correlation between the amount of mass added by thickening and the amount of mass removed by drilling. It's just more variables that will effect the thermal properties of the rotor.

Now, without trying to beat a dead horse, how does this not help braking when lapping? If I understand correctly, Baer increased the thickness of Eradispeed rotors to compensate for drilling all the holes. And the holes do not go through the cooling fins. Now at least that's what they wanted us to believe. But I have yet to see even a single road racer feeling confident enough to take them out on a track. Is that not counterintuative; doesn't Baer have a responsibility to jump all over any false advertising and claim that their rotors are beefy enough for open track? In fact what you will see is it's far easier to simply buy another rotor.

Don't get me wrong, I'm not advocating the usage of drilled rotors for hard lapping at all. Nor am I saying you should get distracted by the amount of media frenzy of all the cross drilled fandango. Rather I'm trying to illustrate that there is less chance of a rotor overheating if there is ducting. If you mention to a manufacturer over and over and over, there is an increased possibility they might respond and add thickness to the rotor, or alternatively recommend going to another line of product. But that involves research, developement, and considerable chunks of testing in various applications.

mitchntx

iTrader: (14)

How about answering the question with a question ...

If you can get more mass and gasses are not an issue, why would you WANT to drill them, but for weight?

lsx24

iTrader: (45)

Well I'm glad you mentioned that Mitch. I considered the Baer/Alcon 4-piston setup for quite some time. It was a 13 or 14 in rotor and the Alcon caliper iirc. Pads are easy to get.

However the 13" rotor was thick enough to be great on the street, and with slotting options would look good too. But to step up to the 14 inch two piece hat/rotor combination would run some serious dough. I have no personal reference whether or not the Alcon setup is available for quite some time, nor how easy it is to adapt to an fbody. It might take some work to make it work.

Instead, I'm considering rotors for my Porsche kit now. I have all the hardware in the attic and have not looked into shipping and time. Actually the thing is, the only cross drilled rotors that Porsche sells is on backorder from what my sources research. They are not easy to get! This means that I either have to wait till after the drivetrain is sorted to complete the brakes, or look for another 'kit' without cross drilled rotors that are not on backorder and can install immediately. If you have any suggestions on options or prices I would certainly appreciate any opinions or feedback, but that's the scoop.

So, long story short, there are only a few select options and those are going to be difficult to complete with a certain time frame. Regarding brakes in general. And I'm not sure if I want to have rotor blanks drilled at a machine shop because that would weaken the structural integrity of the iron piece, and that sounds somewhat jerry rigged to me. Porsche rotors have known to be good during club races and hundreds of hours on twin turbo 996s. I suppose it depends on the application, and what kind of heat you drive into the rotor, but cost would be a factor as well. So an option is to save for a short while and then look at availibilty and pricing end of summer for a solid rotor or drilled rotor kit, as I'm in process of moving to Phoenix next couple days and have an HPDE even scheduled there in May I may ungrade rotors and pads before then but cost and time is a factor right now.

lsx24

iTrader: (45)

I forgot the mention the application is track days and canyon carving for a daily driver.

mitchntx

iTrader: (14)

It depends upon your source, I guess ...
http://frrax.com/rrforum/index.php?a...f=13&t=3837&s=

As for those fantastic Porsche rotors, I had Porsche 996TT brakes adapted to the fronts on my car. After a 20 minute session with PMS enduro pads (Hawk Blacks), tiny cracks formed around 50% or more of the cast in, chamfered holes. And each hole was almost completly plaugged with coagulated brake dust.

Why did I use CD rotors? It's all they offer ...

HPP

Porsche's rep is a little overblown and unearned.

I remember reading somewhere once that Dr. Porsche was all about refining something until it was perfected. This suggests that the famed 911 is simply an out dated idea that continues to linger because there's always refinements to be made, not because it's an inherently good design these days.

The theory is sound, sure - easier to put larger rubber in back, so put the engine back there for increased acceleration traction, and for having more traction to move the heaviest chunk laterally, while simultaneously reducing mass in front which would work better with the necessarily smaller rubber, and cut in quicker, particularly when the added traction of weight trasnfer comes into play.

Sounds like a total win/win all around. Trouble is, they are notoriously twitchy. And while it may indeed be a great solution within the traction limit, if you end up past that point, for any reason, you stand a very good chance of swaping ends. And you are also more prone to acceleration understeer as well.

I guess my point is, just because the might Porsche does something, doesn't make it inherently better, or even "good" in absolute terms. Yet I can't but think that many people who swear by CD rotors do so because they are used by Porsche.

Jpr5690

iTrader: (13)

WOW! TRACK BIRD THAT PRITTY MUCH SAYS IT ALL, i feel good now knowing i got some good pads on the way along with my generic rotors...... the only thing i can think to add to this was taken from a raybestos ad i once saw.. in it they showed a cross sectional view of a "white box" rotor and theirs and then a factory rotor there was differences in the design of the vaneing inside if the rotor that they said made a substantial impact in the cooling copasity they also said that cheeper rotors can be made of lower quality metals that dont repsond to abuse as well.... but this all came from a pamplet i was reading so who the **** knows.....just my.02