[ADHD]

Originally Posted by Ron************

What's interesting is bmw's new performance rotors, they have cross drilled in slotted format! Thats a pretty interesting design thats for sure, I wonder if we'll see other manufacturers jump into making it - I would love to see some testing on that design.

Any pics of these bmw rotors?? Thanks for taking the time to give a detailed explanation...

[Ron@Modbargains]

Originally Posted by ADHD

Any pics of these bmw rotors?? Thanks for taking the time to give a detailed explanation...

Here is the BMW rotor I was referring to, what I like is how they did the cross drilled in the same proper distance that the slotted would have. I just wonder if this even works, or is a gimick. I know this is only on a replacement rotor, but I am interested in seeing if the BBK world will embrace it. I'll be asking Brembo/Stoptech etc on their opinion on the design - I am more interested on testing results which brembo probably has by some of their F1 teams.
It's great to see new approaches and people trying to innovate.

[ADHD]

^^^ very nice!!! thats bmw oem replacement????
How much they run??

[sg335]

Looks like the same OEM european floating rotor BMW uses for the E46 M3 and I believe the E36 M3, which is a floating rotor with 15 rows of cross drilled holes. The holes are drilled in the direction as the directional interior veins of the disk. And also like the stock units, the hats are "floating" from the disks via spindles that connect the two pieces. This provides better cooling. I don't know if the hats are aluminum. I use the same rotors without the holes on my E36.

[PIMPIN THE E92]

drilled and slotted look the best...not sure about performance

[ADHD]

Originally Posted by PIMPIN THE E92

drilled and slotted look the best...not sure about performance

thats the whole point of this thread to find out what is better for performance!!

[purplewidow]

have drilled on all our AMG cars and not one of them has had a problem....they aren't going to crack unless your tracking it all the time!!!

[Ron@Modbargains]

Originally Posted by ADHD

^^^ very nice!!! thats bmw oem replacement????
How much they run??

They are in their performance catalog, they are ridiculously overpriced as most of the pieces they are selling are in their BMW catalog. You could pickup a great OEM replacment rotors- drilled or slotted from stoptech or brembo - we'll have them up on our site soon. As to their design I will see if we can get a company to do the same design setup. I still dont know much about how effective that design is on replacament rotors - but it is innovative, I like their thinking.

[midlife]

Originally Posted by Ron************

Do I dare jump into this thread??? .....here goes.

Lets see I've had this argument in the **********s office about 20x last year or so, so we kept going to all these different sources for information. Eventually after sifting through everything, I'll break it down as simply as possible. Even addressing what I've just read in this thread seems like the typical thread I've read on many forums.

Cross-Drilled -Out performs slotted - False. Best Performance on the Street- Yes one could easily make that argument. I'll get into it.

Cracks- easier with Drilled - Not necessarily, since you wanted personal experience (I've cracked every type of rotor even blanks, and yes some serious cracks) Multiple factors contribute to cracks - the main reason being that the rotors are worn down. Stress fractures are still ok to have on your rotor it doesn't mean its bad yet, but if the fracture/crack is going from one hole to the other hole then now you're in need of replacing the rotor, same if the crack travels to the edge. Other contributing factors are the brake fluids used, and the heat cycles that the rotors go through. Each rotor has different ratings, hard to say this right now cause there are BBK rotors and replacement rotors which are different. A replacement rotor is typically cross drilled right through - that is not the proper way for a cross drilled rotor to be made, it should be cross drilled mathematically in proper areas both sides of the rotor being completely different actually - you'll see this on the BBK's from any of the major companies. short answer - debunked myth/with slight truth in it.

Cooling is better with the Cross-Drilled- does it dissipate heat quicker - Yes which helps performance somewhat - but who here is driving on some serious track races and needs that type of cooling? Your brake fluids you guys use is going to be more important down the line. Anyway short answer - yes helps cooling.

Cross Drilled Rotors- eat up at the brake pads quicker acting like a shredder- sorry not true, I believed that one cause it seemed to make sense. That it gave an uneven wear on the pads. The reality is it doesn't eat up the pads any quicker, if anything they last longer, meaning they are actually the street pad most would want. Short answer - they are fine on the pads.

Cross Drilled - are better in the rain - I remember reading about the answer being true - I don't remember the reasons but the water passes escapes through the holes.

Cross Drilled - less weight - reality the weight difference is negligible. No this don't really matter on the weight, you can save more some where else. Don't do it on your brakes!!!

Slotted - Better for performance- yes this is true. Reasons being is that each time the pad goes through the slate of the rotor, its cleaning the pad one more time through. Its giving a clean swipe on the pads each time.

Hence this cause's - Pad wear down much quicker. Cross-drilled wins between the two in the longevity on pads, hence making them better for street. But Slotted perform better making them better for the track/performance.

Looks - well this is subjective. So you can all have your own opinions on this. But Cross drilled wins on looks in my opinion - I like the way it looks for the street.

Cross- drilled - Street Choice
Slotted - the Track choice

Now to debunk some statements made on here.




Asked this question of Brembo is the only real brake company out there for the F1 - Reason for it is certain race teams want to experiment with different rotors/ for different settings. In the end the majority more then 75% all use slotted. Brembo indulges them in the experiments, some for rain purposes, and to gather data by different race teams, plus other various reasons each team has. But slotted is the choice on the track and what is proven to work. - Please no one starting bringing up the Ferrai Enzo or other super cars with the cross drilled -I asked this as well -Answer: Looks, its not unsafe and they know the person buying that car is rightly concerned with the looks being of major importance. The other reason is those buyers are driving a car built for the street.



Where is this bold statement coming from?? No drilled rotors are safe and used by Porsches, Ferraris etc in their OEM rotors. There are increased benefits from uising Drilled rotors as mentioned above.



Yes, you are right say they stay cooler. But the cracking again is not the main issue. NASCAR uses slotted on their vehicles that are actually racing(not talking about their show cars), I am wondering why people seem to not notice this.



There is a reason these companies dont want to sell into distribution like how most vendors get them and just sell without being informed. It's mis-information that non-direct vendors end up generating. Reasons for both is again to give the proper the choices based on each customer's driving styles/abilities/purposes and matching him up accordingly.

My 2 cents into your discussion. Again welcome to ask me any brake question or discussion you may have in terms of replacment brakes or Big Brake Kits. We carry replacment brake rotors from Stoptech/Brembos, multitude of different pads, BBK's from Stoptech/Brembo/Wilwood, not all of our stuff is up on the site but I'll be working on getting it up there for you guys in the coming months.

bump

[stressdoc]

Materials are more significant than surface effects. There are unavoidable compromises in using alloys that have lower residual stresses (more durable going through heat/chill cycles to avoid stress fractures). Ceramics have better material properties in this application.

[6Zylinder]

I prefer slotted discs because they actually clean the pads in daily driving. They also prevent the pads from getting glazed. The drilled discs as far back as the 80s go, were optimized for wet weather breaking. With the 335i break drying feature I'm not concerned about it. IMO, the pads, the disc size and break caliper is more important than slotted or drilled. I'd rather have 6 pot than floating though.

[6Zylinder]

The choice is yours.

[de.abeja]

JGTC-N1 skyline


Rally Evo


JGTC MR-S

AP racing and all of them slotted.

And for those who really need to stop quick, we have the carbon fiber disks.



Some Formula car carbon- not slotted or drilled! Also AP racing

All the guys I know who run fast street cars at autoX and Solo etc... all run blank discs, the most surface area for the most friction. Then all of them will tell you the obligitory "crappiest OEM system will still lock up bad tires...blah...blah...hoosiers...blah...blah...bla h.

I would rather have larger diameter blank rotors floating on aluminum hats than drilled and/or slotted. My .02

[Ireland]

for performance drilled but slotted look way better

[ADHD]

[spacedogg]

Rob from UUC Motorwerks posted a very detailed post awhile ago. Essentially he stated that drilled rotors are mainly for the marginal weight savings. (They do look sweet though.) He recommended regular or slotted brakes for performance. Drilling, originally, had nothing to do with enhancing cooling. In fact, poorly designed, drilling can actually hinder proper cooling.

http://www.e90post.com/forums/showthread.php?t=43656

Cross-drilled rotors were originally designed to reduce rotor weight. That's an odd concept to sell to a street user, so the industry came up with this "enhanced cooling" myth.

There are often heated debates about whether rotors should be drilled or not, which I frankly never understand... the problems, proofs, and examples of the downside to drilled rotors is overwhelming, and without proof of benefit.

The reality is that in terms of cooling, a conventional vented rotor without drilled holes cools better and has a more consistent cooling spread across the entire surface.

The rotors that I am recommending people avoid are the type that are a standard rotor design that is then simply drilled. This is different than a rotor that is designed with holes in the first place. As far as I know, no aftermarket rotors fall into this category... the only "designed-in" holes are the original equipment rotors from BMW, Porsche, and a few other marques. Beyond that, rotors that are simply "drilled" are prone to heat-induced stress cracks, eventually resulting in catastrophic failure of the rotor. This is principally due to the interruption of the metal grain structure formed during casting, creating a "stress riser" affected by differential temperature. The OE drilled rotors are usually "cast perforated" - the holes are cast into the disk in the first place, allowing the metal grain structure to form around the perforations, thus maintaining strength. BMW Motorsport uses such rotors on the E46 M3 Competition Package, Z4 M Coupe, and E60 M5 (and likely on the new M3 when released).

If you examine the BMW brake system (and look at the racers using brake cooling ducts), you will see that the rotors have a central inlet on the back side of the rotor. This is designed to take cooling air in at the center and literally act as a centrifugal air pump to move that air through the rotor, cooling it evenly throughout the entire radius. Cross-drilling this type of rotor "short circuits" the cooling path, allowing all the cooling air taken in at the backside/center to exit frontside/center... never getting to the extreme radius, which is the hottest area in need of most cooling.

The only form of cross-drilled rotors that should ever be used are those that are designed that way... not the same as a solid-face rotor that is drilled. Rotors that are designed with holes often have a different internal vane structure that takes the holes into account, allowing for proper cooling.

I generally prefer more than a one-line "FAQ" answer to questions like this, which is why I prefer the competition car in-depth information provided by Wilwood, who quite simply are the largest manufacturer of competition brake systems and rotor components in the USA:

"Caution on drilled rotors: There is a common mis-perception that rotors are drilled to improve cooling. The reduced mass of a drilled rotor will dissipate its retained heat quicker, but it also builds up heat at a much faster rate. The decision to use drilled rotors should be solely based on the merits of the lower rotating and unsprung weight, and not for improved cooling. It is not wise to use drilled rotors in sustained high heat on hard braking tracks unless the team budget affords a high frequency of rotor and brake pad replacement."

"In categories where every ounce and thousandths of a second count, drilled rotors provide maximum weight reduction. For heavier cars, or cars competing in bracket or throttle stop categories, the additional mass in the solid face rotors provides higher thermal stability and will increase the service life of the rotors and pads."

Now when a company tells you not to buy one of their products because it's not suitable for your type of use, they earn my respect in a very big way. There's no marketing involved... just the plain facts.

By the way, remember my first post where I said "There are often heated debates about whether rotors should be drilled or not"?

[judec]

I've seen that quiet often. Not the case of all drilled rotors, but quiet a lot of them

[TurboFan]

Originally Posted by hunter399

Here's a post that I did that summarized thoughts about slotted vs. drilled vs. normal.
--------------
Darrick Dong; Director of Motorsports at Performance Friction: "Anyone that
tells you that drilling makes the disc run cooler is smoking crack."

Power Slot: "At one time the conventional wisdom in racing circles was to cross-drill brake rotors to aid cooling and eliminate the gas emitted by brake pads. However, today's elite teams in open wheel, Indy and Trans Am racing are moving away from crack prone, cross-drilled brake rotors in favor of rotors modified with a fatigue resistant slotting process."

Stop Tech: "StopTech provides rotors slotted, drilled or plain. For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors." (Note that even though Stop Tech sells both drilled and slotted rotors they do not recommend drilled rotors for severe applications.)

Wilwood: "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."

From Waren Gilliand: (Warren Gilliland is a well-known brake engineer in the racing industry and has more than 32 years experience in custom designing brake systems ...he became the main source for improving the brake systems on a variety of different race vehicles from midgets to Nascar Winston Cup cars.) "If you cross drill one of these vented rotors, you are creating a stress riser that will encourage the rotor to crack right through the hole. Many of the rotors available in the aftermarket are nothing more than inexpensive offshore manufactured stock replacement rotors, cross drilled to appeal to the performance market. They are not performance rotors and will have a corresponding high failure rate"
From Baer: "What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors? In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads...However, with today's race pad technology, 'outgassing' is no longer much of a concern...Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer's offerings."

Grassroots Motorsports: "Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause
temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean
the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)

AP Racing: "Grooves improve 'cleaning' of the pad surfaces and result in a more consistent brake performance. Grooved discs have a longer life than cross-drilled discs."

+1 wow you just saved me a lot of typing. Thanks

[OC Guy]

Interesting discussion. One must keep in mind in F1, Nascar, etc. they will replace their pads, rotors, etc. far earlier than end of life (if not every race).



Note the slot does not go to the edge. If you see slotted rotors that go to the edge, they are definitely more prone to cracking.

It's interesting to read discussions like this on here, rather than what body kit or what not I should buy for my car. Just a personal note.