ive heared that its drill or is it sloted rotor or is it both together will crack over time.

 

any rotor could crack over time. heat and internal stress is the cause.

 

Drilled rotors are prone to cracking. Under daily driving they will be fine. Keep in mind that drillled rotors, while they tend to run cooler, do not increase braking performance. The amount of braking surface is reduced, giving the pads less area to grab onto.

When in a high stress/high heat situation, a drilled rotor cannot withstand the same temps as a slotted or full rotor. This is when cracking tends to occur.

Rotors on passenger cars are drilled mainly for cosmetic reasons. In auto racing, rotors are drilled primarily for weight savings. Every little bit helps on the track.

 

I second what Bret said.

I went with slotted rotors for my 1LE swap since they will help cool them a bit better, release the gases created by the braking for a better contact patch and not as weak as drilled.

 

Sorry, but this is not entirely true. The only part that you have correct is that drilled rotors will crack easier in a high-heat situtation.

You stated that the braking surface is reduced giving less area for the pads to grab. Let me explain why this is wrong. When rotors are drilled the pads can make full contact to the rotors under hard braking because the gases that build up between the pad and rotor that cause brake fade can now escape through the holes thus minimizing pad float and maximizing contact area.
Under lighter braking, the minutely smaller rotor surface area due to drilled area has no noticible hinderence at all. (you may have to step on the pedal 1/16' max. harder to get the same braking capacity) Once the brakes are at running temp., you have a lot larger sweet spot in the pedal with drilled rotors.

Sweet spot is the area of pedal pressure control from when one first applies the brakes-- to---when the brakes lock. A larger sweet spot will allow you to maintain harder pressure on the pedal with out the brakes locking as soon as the point the stock brakes will lock at. this will allow you to drive deeper and harder into corners without brakes locking as easily causing loss of steering or control.

Brake are not drilled with the intention of weight reduction either. This is where people go to aluminum or carbon rotor hats for cooling and weight.

An added note: You will probably end up in jail long before you ever crack a drilled rotor on the street.

 

There was a time when this was true, BUT today's brake pads are more advanced and do not "gas" so this principal doesn't hold true anymore.

As I'm sure you're aware, Wilwood is one of the leading brake manufacturers for both professional racing and aftermarket performance. Let me share a quote from the Wilwood Brakes web site:

Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight._ Drilling diminishes a rotor's durability and cooling capacity.
Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them._ Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.

----------------------------------------

*Here's some more info. from driversedge.com (a site for BMW enthusiasts):

"Gas slots in the rotor face have several advantages over cross-drilled holes:

1.Since brakes are essentially heat-sinks, the more mass you have the better you are. Bigger IS better. When you drill a rotor full of holes, you remove quite a bit of material, and drop the surface area under the pad. This places greater heat stress on what's left, and this is one of the reasons why cross-drilled rotors tend to warp so fast. While there is an increase in COOLING surface area, this is overshadowed by the other factors.

2.Since the internal webbing is only drilled through occasionally, it is usually necessary to re-balance the assembly. Gas slots are only .050" deep, and there are only three grooves per side. Significantly less mass is removed, preserving the brakes' ability to absorb heat. This is especially helpful for autocrosses and driver's schools where rotor warping is common.

3.The entire pad is swept as the groove passes, as opposed to only where the holes would pass. This greatly enhances wet weather performance, and allows removal of the brake backing plates, almost doubling the airflow to the rotors.

4.Because the slots do not go all the way through the rotor, the structural integrity is much greater, and in fact approaches a stock rotor."

 

Hey your the expert.

I'll just smile and wave as I'm passing you into the corners.

"Pads don't gas anymore" whatever you want to say, you obvious don't have any understanding of friction or chemistry. Gases are always produced with friction.

Your quote also says "Partly a carryover" This means that it is merely one reason of many in the development of drilled rotors. It was started in an attempt to reduce weight, but was discovered to in the act to have more positive use than any weight benefit. This is a common thread in any research and development process.

As for the comment that " they have become popular for street use from pure aesthetics value." This is also a true statement but carries no value against the use of dilled rotors. Every one likes them because of the looks--- thus SOME manufacturers took things too far and excessively drilled rotors only for looks and not function thus severely weakening them. Those would be the ones to stay away from. Rotor thickness and drill spacing & offset are critical to durability. This is why one should not drill rotors yourself or just have any machine shop do the work like you would see on many show cars. The drills have to be engineered properly.

ITS CALLED MARKETING. Wilwood spends alot of money on advertising to get you to buy their product. The thing I most don't understand with your quote on Wilwood is that their final phase of " we sell many types of drilled and slotted rotors to choose from " actually goes against what you are trying to state. Why would they offer drilled rotors if they are so bad? Slotted rotors are stronger for allout racing heat (I agree with everything you stated about strength and warpage, But this was not the subject I argued) Drilled are better for daily driving than stock and DO improve street preformance over stock rotors.(this is the basis of my arguement, don't get off on a tangent. You stated that drilled rotors do not improve braking preformance, they're just for looks)

 

If you read the quote correctly, this comment refers to slotted rotors not drilled.

Okay look, I'm not trying to argue here. I'm just trying to pass along valuable information. So your comment is uncalled for.

If you go back to my first reply in this thread, I stated that drilled rotros are fine for street use. I also wanted to provide some info. for those considering using their cars in racing/high stress situations. Drilled rotors in high stress driving aren't going to last as long. If you have the budget for it, then that's probaly not a concern.

My car is driven daily on the street and currently has drilled rotors in front. They made no noticeable improvement on my car. When my 1LE upgrade is complete, I'll be running slotted rotors at all 4 wheels. That's my preference.

The biggest improvement anyone can make to their brakes is to upgrade to larger rotors. Regardless of what style rotor you run, you will see a noticeable improvement.

So do all the other companies. Most claim that if you just install their brand of cross-drilled rotors, your car will perform like a race car. Wilwood is being honest. They aren't making any outrageous claims.

 

Cross drilling and slotting are a carry-over of old technology, when outgassing was a serious problem from older brake pad materials. Manufacturers still make them simply because people still want them, whether because they perceive some performance advantage, or they simply like the looks. All the GOOD manufacturers simply promote and market them as asthetic features (such as Baer).

Want proof? Look no farther then Formula 1 and Nascar. Too distinctly different styles of racing, yet two racing organizations where the teams use solid brake rotors, completely void of any sort of cross drilling or slotting. While it's arguable that braking is not critical in Nascar, I don't think anyone but a fool would argue against the need for quality braking in Formula 1. I don't watch enough of the other forms of racing to comment on them, but I would hazzard a guess that most of them also use solid brake rotors, because with todays materials that would give them the best brake performance they could get.

From a professional racing standpoint, cross drilling and slotting were historically done to address outgassing problems, which have been eliminated through the use of superior brake pad materials.
This isn't true. Friction produces heat. All other results are a byproduct of this heat (with perhaps the exception of material wear, which is still probably heavily affected by heat) Gases form when temperatures reach the point where the material will enter the gaseous state. This temperature is dependant on the material. Using our most basic example of water, it boils at 212 degrees because this is the temperature where water becomes steam, or rather, where it goes from liquid to gaseous form. The materials in older brake pads would become gaseous at relatively low temperatures, in the several hundred degrees range, and thus was a problem with heavy braking. Now scintered metals, carbon fiber, kevlar, and other such materials have a MUCH higher tolerance to heat. These materials require temperatures in the thousands of degrees range to form gases, temperatures that are not seen even in Formula 1 racing. As such, gases are NEVER formed with pads made of these materials. Is that enough Chemistry for you, or should I break out my old Chemistry textbooks and get down to the nitty gritty of it?
So, with newer brake pads made from these superior materials, cross drilling and slotting become unnecessary. Nothing more then cosmetic modifications, even in the street/strip environment. Weight reduction can be achieved far easier by changing rotor size. Inner and/or outer diameter, as well as thickness.

 

Thank you jRaskell.

 

Nascar and F1 are under strict restrictions as to what they can run parts wise.this keeps the speed down and less strain on suspension parts and driver. G's keep getting too high and parts break.

Trans Am Series cars on the other hand do not fall under these restictions and every car runs their own version of slotted rotors to off-gas the pads! Yes still today even with new technology.

Certain types of basic street pads produce a very low heat/friction grip and have realitively no variance when combined with drilled rotors (semi-metalic for example). Performance or racing type pads come in a variety of different materials to improve friction coeficients. With these type of pads come gases. Most cross-drilled rotor manufacturers will recommend a performance type pad to be used in combination with the rotor to utilize the added effectiveness of the drilled rotors over stock brakes ( usually a carbon-matrix material pad). When these pads are used with ordinary rotors, the braking improvement is there but is not near the sweet spot that the pads will have when combined with drilled or slotted rotors.

What you guys are preaching about drills and slotts not being necessary is true under your senerio with regular everyday street pads but not with most performance type pads. These run at higher temps because of (obviously) higher friction and gases forming.

 

JRaskell, Tell me then what causes brake fade? Even with the your miracle non-gas forming brake pads?

I'd like that chemistry lesson.

Everything I preach when I give advice with cars is that " You must have parts that are married or compatible to eachother for things to work great, not good, great."

 

Boy, it was not my intention to create a heated debate, but you have to admit it is educational, if not interesting.

Okay, I've drug out the "Brake Handbook" by Fred Puhn, ©1985.

Quoting the book: "Brake fade is usally the direct result of high temperature, so first consider cooling modifications and harder linings."

Performance brake pads are harder than regular everday street pads. Again quoting the book:
"Hard Street Driving - Use heavy-duty friction material for hard street driving or hauling heavy loads. This is usually a semimetallic lining. Heavy duty material has greater wear resistance and better braking performance at high temperature."

This is why the more extreme performance pads don't operate well when cold. They NEED heat to work properly and aren't suited very well to everyday street use.

Regular everday street pads operate best at lower temps and tend to fade quickly under hard use.

 

This is a riot. There is absolutely nothing miraculous about it. Every material has a certain temperature at which it transitions to the gaseous state. Below this temperature it is not a gas. Above this temperature it is a gas.

Water becomes a gas at 212 degrees
Iron becomes a gas at 2750 degrees
Carbon becomes a gas at 4827 degrees.

I don't have the numbers for steel, because steel is a composite made of iron and carbon, so figure it will be somewhere between the two depending on the percentage of carbon and iron that are used, not too mention there are various steels out there that increase or decrease the carbon content to tailor the properties of the steel for it's usage. High iron content means good stength, but brittle. High carbon content means less strength, but more malleable and better high temperature properties.

So it's pretty simple to understand. If you use carbon fiber brake pads with steel rotors, you need to reach temperatures upwards of 2700 degrees before any gas forms. I can assure you there are NO brake systems out there that reach those temperatures, because your rotor would literally melt before that occurred, since the melting point of steel is close to 1000 degrees lower then it's boiling point.

 

I'll answer my own question. Brake fade is caused by excessive heat causing gaseous build-up between the pad and rotor. In this circumstance, no matter how hard you press the pedal the pads will only float on a gaseous layer between the pad and rotor and will not bite even with excessive pressure.

Try stopping your ordinary brakes twice in a row form 100-0 mph and I promise you that you will exceed your first stopping distance by far. My drilled rotors will stop just as fast the second, third and four consequetive times.

Gases are formed from heat alone, not the vaporization point of the metal. Water is in the air (In case you may have forgotten) and condensation form the rotor heat in contact with the air alone can and does build up gases.

 

Let me start by saying that this is not intended as a flame. Just a continuation of a rational discussion.

With that said, I still feel you are "over stating" the issue of gassing.

Here's info. from the Baer web site. I've highlighted key statements:

"Yes. Although there are some companies which sell cross-drilled rotors as an actual performance upgrade, in our extensive testing we have seen no improvement to be had by simply crossdrilling stock rotors. This is why Baer has developed EradiSpeed™ rotor upgrades for a variety of applications. Although it is true the crossdrilling, the slotting, or for that matter the zinc surface washing, are cosmetic enhancements, EradiSpeed™ rotor packages also feature rotors with thicker cheeks to provide more heat sink capacity in the fire path of the rotor. Also, they all feature directional vanes for greater pumping efficiency, as well as a two-piece design where the hat, or hub/hat section of the rotor is CNC machined from a solid billet of aluminum and is then fixed to the rotor ring using National Aviation Standard (NAS) stainless hardware. In other words, the EradiSpeed™ is much more than just the most visually appealing direct replacement rotor, it is the only upgrade of its type which can actually deliver the benefits of greater heat absorption, increased durability and lighter total weight.

In racing, crossdrilling was designed to alleviate a problem known as out-gassing. In some of the older pad compounds, when the pads reached elevated temperatures consistent with performance or racing use, the binder (that’s the material that holds the friction material in place) boiled off, producing a gas. This gas would build up between the rotor and the brake pad, effectively keeping the pad from directly contacting the rotor. The holes provide a relief path for these gasses, as do slots, so the pad can once again contact the rotor. Crossdrilling was NOT designed to facilitate cooling.

Although Baer offers crossdrilling as an option on their systems, it is offered as a cosmetic option only.
However, with an EradiSpeed™ rotor upgrade, unlike a cosmetically altered stock replacement rotor, you will benefit from improved durability, greater heat sink capacity, lighter total weight and the visual excitement of a 2-piece, aluminum centered, crossdrilled, slotted and zinc washed appearance.


Next:
Key word there is "excessive". YES, excessive heat causes fade. However, Carbon Metallic or other high performance brake pads are designed to operate at a much higher heat range. To push them past their designed range and into "excessive" takes quite a bit. You'll never get them into that excessive range in daily driving on the street, therefore they won't gas and fade.

With the more extreme performance pads, you'll have a hard time getting them into their ideal or "sweat spot" range.

Last:
I currently have cross-drilled rotors on my GTA. They are the standard stock diameter (which we all know is too small) for our cars. My car doesn't stop any better than it did when it had full rotors.

I won't see any serious improvement until I install my larger 1LE rotors, because I will be increasing the braking surface area.