When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Sometimes it's easier to post the content of some articles within this discussion for some who like to read about this stuff below:This article was originally posted by Modified Magazine. Click here to read it.
We’ve received quite a few emails lately asking us to explain what the advantages are of cross-drilled and slotted rotors, as compared to the blank rotors most cars come standard with. We’ve also had requests to explain why many slotted rotors these days have curved or J-hook shaped slots, rather than straight slots. Rather than giving you the Wikipedia answer, we went right to the source by once again contacting Mark Valskis at Brembo North America (some of you will recall his contribution to the big brake kit Tech Talk story in the May ’11 issue).
As most of you already know, the basic function of a brake disc is to provide a mating surface for the brake pads so that when you stomp on the brake pedal the friction material that makes up the pad is squeezed against the rotors (by the calipers), converting forward motion into heat as the car slows. That heat is then radiated to the atmosphere as air flows over and through the rotors (and the rest of the braking system), completing the conversion of kinetic energy into thermal energy.
According to Mark at Brembo, cross-drilled rotors came into being because of the need to evacuate gases or water from the interface between the disc face and the brake pad surface. As Mark further clarified, “Modern brake pads don’t have an issue with out-gassing like they did many years ago, but the cross-drilling is still helpful for use in wet conditions, especially when the pad surface area is large. Additionally, cross-drilling increases the surface area of the disc, and this aids in disc cooling (one factor in brake disc cooling is the ratio of surface area to disc mass). The most significant feature of the holes (when done correctly) is that they continually refresh the brake pad surface, providing improved performance and greater disc life. As the holes pass the brake pad they essentially clean the surface, helping to prevent pad glazing or hardening. This effect can be easily observed on a drilled disc near the outer edge where there are no holes. In this area, the pad surface is not refreshed and you will typically see greater disc wear in this unswept area.” It’s also worth noting that this type of pad refreshing by cross-drilled and/or slotted rotors helps maintain more consistent frictional performance.
Rotor Education Tech Talk Cad Drawing These CAD drawings of a slotted and ventilated Brembo brake disc illustrate just how compl
Some of you may not be fans of cross-drilled rotors because you’ve seen cracks in the disc surface radiating out from the drilled holes, but as Mark points out, not all drilled discs are created equally. “Brembo has a long list of requirements for drilled discs. First, the holes are not just simple cylindrical holes. They have a more complicated shape that requires special tools to create. We also have strict requirements on hole density or the number of holes per given surface area of the disc. Additionally, there are requirements for the hole size and placement of the holes, including distance between holes, distance from braking surface edges, distance to disc vanes, angular offset of holes and more.”
But even with the highest quality cross-drilled discs, there can be issues with thermal shock and fatigue around the holes when using very aggressive racing brake pads. As Mark explained, “Slotted discs were developed to provide the benefit of refreshing the pad surface, while being able to be used with top-level racing friction materials. Drilled discs provide the same benefit [refreshing the pads], but also increase the cooling of the brake disc. With top-level racing materials, the heat input is very rapid and the increase in localized cooling around the holes can cause issues.” So slotted rotors were developed as a solution to a very specific problem associated with extremely aggressive friction material normally associated with racing, though if you’re anything like me and run some pretty aggressive brake pads on the street as well as at the track, then slotted rotors may be the right choice for your car.
Rotor Education Tech Talk Cross Cut These CAD drawings of a slotted and ventilated Brembo brake disc illustrate just how compl
As for the shape of the slots, Mark had this to say: “The different design of the slots is due to extensive research and development, including [brake] dyno testing. Due to the fact that track testing is required, and thanks to strong collaboration with many top-level racing teams, Brembo has developed a very broad knowledge of the many different types of slot shapes possible when machining discs.” Since this type of extensive R&D is really outside the scope of all but the biggest brake system manufacturers, a lot of what you’re seeing in the aftermarket are companies copying what leaders like Brembo are doing with respect to slot shape, slot spacing, slot depth and so on.
Ultimately, the slots are all designed to do the same thing (refresh the brake pads), but different shapes no doubt impact the aggressiveness with which the pads are refreshed and also likely affect localized cooling of the disc. And speaking of cooling, the internal structure of ventilated rotors plays a very important role here. “The mass of the disc is the determining factor in how much energy the disc can absorb, while the design of the internal geometry helps improve the disc’s ability to shed the heat,” Mark explains. “The key factor in the use of a vented disc versus a solid disc is the increase in the ratio of disc surface area to mass. Heat transfer to the air occurs only on the surfaces of the disc that are directly exposed to air; so the more surface area, the better the disc can shed the heat.”
Rotor Education Tech Talk Display Model This NASCAR braking system provides some interesting insight into disc slot design – note
As for the internal vane structure of a ventilated disc, Mark adds: “There are limitless internal vane structures that are possible. Design of the vane structure has a dramatic effect on the performance of the brake disc. Some designs, such as directional curved-vane discs actually improve the airflow through the disc by turning the disc into a centrifugal pump. However, the cost of implementing this is increased due to the need for unique left- and right-hand discs. Brembo has patented a ‘pillar vane’ internal geometry that provides nearly all the airflow advantages of the curved vane discs while being able to use the same disc on both the left and right sides of the vehicle.”
Who knew so much technology goes into these seemingly simple iron discs (the material composition of brake rotors being a topic for another month). But when you consider just how vitally important the braking system is to safety and performance, it shouldn’t come as a surprise that industry leaders like Brembo are constantly looking for ways to improve the design of their brake discs.
Rotor Education Tech Talk David
im sticking to OEM since the car barely gets driven and not even that hard. only thing im currently considering changing out is to ss lines.
any thoughts on that?
OEM drilled are good for street driving. And stainless steel lines are not necessary. That being said, since I track a bit, I got tired of constantly checking the drilled rotors for the progression of cracks. Mine had/ have tiny cracks around the holes but are small enough to not be an issue. However I wanted to be less worried on the track and made the switch to slotted but still run the drilled in the winter.
I do also have SS lines simply because they are an inexpensive mod.
I’ve seen enough drilled OEM Brembos with micro cracking that I am more of a fan of slotted, personally. I have never seen a failure on this platform, but I don’t like any cracks in something so important.
^also curious. I wish more people made 2 piece options for the isf. My brother purchased two piece dba rotors for his g37 for a fraction of what they are for our cars.
The Brembo comments don't apply to our cars. Our rotors crack just fine. Hole do nothing to improve cooling - air moves through the internal vanes because the linear speed of the outer edge of the rotor creates a low pressure area and the air at the center of the hat flows outward into the low pressure region. Holes reduce mass and reduce capacity, create stress risers for cracking no matter how you cut them or mold them, and all the "special" in the world doesn't make them outperform a flat faced disc.
All that said, any disc with any surface - plain, drilled, slotted, combination, etc. is going to crack under hard use. There's no escaping it. So pick your poison and realize it doesn't really matter even for those of us who track our cars. I bought discs from Figs because they're thicker and only slotted, so the extra thickness makes up for the mass lost to the slots a little. Truthfully, you'd be far better off doing bushings before brakes because you can't brake in a straight line from high speed with the OEM bushings, and once you get rid of them, THEN brakes might make a difference. Best thing I ever did for braking on my car was installing solid LCA bushings.
I wanted to clarify the benefits of the 2-piece rotors that we offer as it pertains to the discussion especially on the front of slotted vs cross-drilled.
First of all, the factory rotors and pad combination tend to "wear together" as the ductile iron used is a softer formula and you will see this in the radial rings that form when the factory and replacements rings wear down.This is one thing that you will see is that over time you are replacing both the pad and rotor together. The softer alloy contributes to the fatigue of the iron as it goes through temperature cycling and that is the cause of the fracturing and radiated stress on the iron material. Couple that with the fact that most of the softer metallic pad compound fills the holes, the effectiveness of a cross-drilled rotor and the benefits are pretty much defeated.
I made a diagram this morning to show some of the features and provide closer details of those features.
The biggest things I would emphasize are:
The rotor material: The alloyed gray iron is extremely hard in comparison to stock. This improves wear, thermal capacity and stability, uniform expansion and contraction, and overall rotor life. You will likely never need to replace the rotors again is used on the street and on track when coupled with the correct pad, you will also have much longer intervals and wear characteristics. Our endurance teams use these in conjunction with the larger BBK calipers and they have been able to go an entire season on the same endurance pads and the rotors are not even showing wear.
Open-Slot: This is a feature that Lobux was talking about and the best part about this Patented tech is that is it cast into the rotor. So the structure is integrated and it also windows the internal vent design. It maximizes cleaning action while also creating larger escape paths for the heated air and gas at the friction junction.
The hat material: Our hats are forged, just like a wheel, and then post machined. This means the grain structure is aligned to the end-use, vs just simply making it fit. The pickup tabs on the hat see a lot of stress based on being the primary thermal connection between the rotor and the hat, so this structure is important. It also allows the ring to be center-mounted.
Center-mounted rotor ring: This midplane mounting means the rotor is mounted from both sides of the casting. This allows for uniform expansion under cycling, greater air availability to draw into the cooling vanes and the economy of leveraging RH and LH rotors without unique directional castings on both sides. This means we deliver more value as the rings are less expensive to replace, while also be a better design.
Thicker rotors and convergent cooling vanes: It's a hidden detail, but the internal design of the cooling vanes does matter as the air requires turbulence to transfer heat. So it's just about airflow, it's about disrupting the boundary layer of the airflow. The RB rotors do this with vanes that focus and disrupt into turbulence, making the rotors recover faster. This in itself is a huge benefit because it allows us to run a milder pad on track, generate less total heat, accumulate less heat, and recover braking faster. Heat is the enemy here and the more you can manage it as a driver the better you will be. You may be able to push things to get that last little bit out of the brakes in a time trial format, but in endurance racing, it is more about the total accumulation of heat, resource wear, and what that means to have one less pitstop or in the case of HPDE, a full day on track and getting your money's worth.
We are devoted to the performance of the platform and have tested many solutions over the last 15 years to team up with RB on many of these solutions. They are total solutions with pads designed for the rotor and the environment and they are meant to complement the enjoyment of your track day. Proper bed-in, resource management, and driver adjustment are all part of that system, so there is some aspect that you will need to take responsibility for on track. In addition, we also offer street specific pads that are low noise but still reduce dust and provide good bite. They work best with these rotors, but can also be used on factory rotors.
Beware of thinner faced replacement rotors: When I initially bought rotors to test from Raybestos, the face of the rotor was about 3mm thinner than the factory Brembo discs, this will make all of the above even worse, so know what you are getting, what alloy you get is just as important as the tires compound you run, and picking the right pad compound for your driving and modulation needs is also a keep factor.
Just trying to help, I do not post a whole here anymore, but rest assured we are still supporting what is demanded on these chassis as they age especially and trying to deliver the top overall value to our customers in the long term.
Thanks, Mike
__________________ Redefining Lexus Aftermarket Parts Since 2001 -- We are your Lexus suspension experts--
BCR - KW - PENSKE - OHLINS - HKS - GREDDY - STANCEPARTS
Links - Arms - SuperPro Poly Bushings - Solid Bearing Conversions - Motor Mounts
RB BBK's and 2P Rotors, G-Loc pads, Radium Fuel Systems
Custom Fabrication Design and Machining - Industrial 3D Printing - Laser Cutting 2018 USTCC Sportsman Class Champions - 2018 NASA ST5 National Champions
11-13-20, 12:04 PM
found the front , but still searching for the rear profile to fit the F
Spill the beans....
