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View Poll Results: If replacing your discs, you would chose

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  • OEM stocker discs FTW!

    4 10.26%
  • DBA slotted

    31 79.49%
  • DBA slotted and crossdrilled

    4 10.26%
  • Rotora crossdrilled and slotted

    0 0%
  • Rotora slotted

    0 0%
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Thread: Opinions on Front Slotted & Cross Drilled Brakes

  1. #21
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    Quote Originally Posted by Nuliaj View Post
    I don't mean this towards anyone in particular as this is just an observation in general, but it seems sometimes people feel the need to justify their purchases regardless of the facts.
    You're probably right to some extent, but there is also sometimes a misinterpretation. Associating slotted with quality is not necessarily accurate, but many people might think that way initially.

  2. #22
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    Nuliaj, Have you tried a set of DBA's over stockers?
    I do not know the science behind it but am commenting on experience.

    When I had my SSS, it definitely stopped shit tins better with the DBA 4000 slotted on the front.. when the rears came up for replacement I put those on too.

    In regards to the rotoras or DBAs, Id go DBA.. support local.. proven quality.

  3. #23
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    Does anyone know the replacement cost of the OEM rotors? I suppose this would be a consideration too! I've found mine to have sufficient stopping power for road use, track would probably be different!

  4. #24
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    Why use drilled or slotted discs?

    Drilling or slotting discs aids the disc in several ways:

    The edges of the slots or holes continuously clean and refresh the pad surface as well as providing increased brake "bite". Additionally, they prevent gasses from collecting between the pad and disc interface.

    The disc is lightened, thereby decreasing its rotational inertia.

    Improved ventilation increases the disc's ability to shed heat, resulting in cooler operating temperatures

  5. #25

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    Quote Originally Posted by kmh001 View Post
    Brakes convert kinetic energy into heat energy. The greater the mass of the rotor the better it will work to absorb heat. If you remove mass from the rotor by cutting slots or cross drilling it be less capable of absorbing heat and fade will occur sooner.

    The slots and holes do not aid cooling, the only technical reason they exist is to mitigate the effects of fade by providing a pathway for the gasses that cause brake fade to escape, but this is a band aid solution. It's better to design the brakes properly so they don't fade in the first place, and the MPS is pretty good in that area as long as the correct pad material is chosen.

    The other reason slots and holes exist is because they have become fashionable, but trust me, they reduce braking efficiency and fade resistance. You would only choose slotted or drilled rotors if your stock brake setup is hopelessly inadequate and plagued by fade and you need to get the gasses out.

    If your brakes have gone off it sounds like they need maintenance, not a redesign. Some things to consider include how many km have they done, whats the pad thickness and rotor thickness? Are the slides well lubed or dry? How long since the fluid was changed? Old rotors that have worn down by 2mm will have lost an awful lot of mass and will fade much sooner. That's why I prefer to discard rotors instead of machining them.
    ^ See kmh001's comments.

    Because I'm too lazy to type I'm just going to quote this from another forum. Brake article I wrote, publishing? - Corner-Carvers Forums

    The Working of Brakes
    There is a common fallacy out there that increasing your brake pad size will increase the stopping power of your car through greater friction. This is in fact false. The force of friction is determined by physics as the force down on the object times the coefficient of friction. The only way to change the coefficient of friction is to modify the material or design of the brake pad. The only way to modify the force down is to change the brake piston force (by size changes or number for example).
    This does not mean that a larger brake pad does not help braking! The benefit of a large brake pad comes into effect when you consider thermal dissipation. The larger the pad the more this thermal temperature (created by the interaction between the pad and rotor) is spread amongst a pad. This means less temperature is concentrated at one point on the pad and the rotor absorbs more heat. This decreases the likelihood that the pad itself will heat beyond operating temperature. If the pad were to go beyond operating temperature it would glaze over resulting in brake fade. Furthermore, a larger pad results in a longer service life of the pad since there is more pad material to consume. **Note: This is not to say that a huge pad is the way to go. I am simply telling you the benefits of a bigger pad. Do not. I repeat do not buy a huge pad thinking that will be the end all. However, consider a pad with a better material makeup for a large difference.

    Cross-Drilled /Slotted Rotors
    The second thing you can do to improve your brake performance is often to go to a larger rotor. We all know that this gives the rotor further ability to dissipate heat away from the pads through itself and through the air (conductive and convective heat transfer). It also increases the effective radius of the force acting on the rotor. Since actual brake torque equals force of pistons* effective radius * coefficient of friction of the pad. So obviously a larger pad, a larger rotor, or both result in better brake performance by avoiding brake fade. It is also obvious that a larger rotor will give you a larger brake torque (stopping force). But what about cross drilled or slotted rotors? Well the common belief in the main stream is that somehow slotted or cross-drilled rotors allow for better performance by handling heat. This is 100 percent false. The individuals involved in such fallacies mention that air through the holes works to cool the rotor (convective heat transfer into the air from the rotor). The issue is that from physics we know that metal transfers heat better then air by a significant amount. (The larger mass of the rotor becomes more important then the larger surface area of the rotor in any situation other then the optimal. Cross drilling is not an optimal manner of creating metal to air transfer through larger surface areas. There is not much airflow through the holes.) As such the rotor begins to work as a heat sink. Now by cross drilling or slotting we are decreasing the overall amount of metal to transfer this heat to. Clearly we are decreasing performance of the rotor to dissipate heat amongst itself. We are also damaging the brakes structural rigidity. The iron in a brake rotor is made of a crystalline structure. By drilling holes in said surface we cut the end grains creating a situation that breeds cracks. Furthermore, even if we were to cut the rotors correctly to avoid cutting the end grains structural rigidity is still decreased. The temperature around the holes will be slightly less then that of the entire rotor leading to temperature stress. Moreover, the decreased mass will result in lowered rigidity. Lastly, the holes of a cross-drilled rotor decrease the area of the pad that contacts the rotor. This concentrates the heat more on certain areas of the pad (similar to the idea of using a smaller pad where the pad heats up more quickly).
    So what do cross drilled and slotted rotors accomplish? Well cross-drilled does not do anything for a car but perhaps give you a certain bling look. In a motorcycle or other extremely light vehicle the decrease in rotational inertia and unsprung mass might perhaps be useful (once other more efficient avenues are exhausted). However, in a street car or race car the speeds and weight of such vehicles will make the relatively miniscule decrease be outweighed by the need for more heat dissipation.
    Slotted rotors meanwhile serve a few purposes. The main original purpose of a slotted rotor was to vent gases that buildup between the pads and the rotors. However, this reasoning is no longer valid. As the years have gone by pads have been designed that produce very little gas. Furthermore many pads come with groves in themselves that allow for the removal of any minor gas that is created. So does that mean that slotted rotors fall to the same fate as cross-drilled? Well, no. A slotted rotor always decreases the rotors capability to dissipate heat amongst itself, but they have their applications. A slotted rotor will clean off the brake pad as it passes the slots. As such it works really well for rally and dirt tracks. Furthermore, the slots themselves can serve to wipe off the top layer of glaze that tends to appear on your brake pads. Some racers say this last part is beneficial while others question whether the slots will fill before the deglaze affect is ever helpful. I have yet to determine the answer to this question. The answer of slotted brake usefulness seems to lie with whether the benefit of cleaning the pads outstrips the loss in heat dissipation. This question depends on your application.
    And guys, if you're not going to listen to me, at least read this article by Crossbow - one of the most respected and technically minded guys in the Mazda community. http_://www.mazdaspeedforums.org/forum/mazdaspeed-3-6-suspension-brakes/1990-crossdrilled-rotors-what-you-should-know-before-buying.html

    MODERATED by Nexus : URL trigerred malware warning, currently modified to prevent a click working. Checking it out....
    Last edited by Nexus; 21-06-2009 at 11:43 PM.
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  6. #26
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    My understanding was that slotted makes bugger all difference to heat handling, gives a higher coefficient of friction and cleans the pad.

    Mu understanding was that cross-drilled will further increase the coefficient of friction (more bite) but weaker and apparently I was wrong thinking that it helped them stay cool.

    How much any of that is necessary if any and whether these products will achieve the result are the questions, yes?

  7. #27

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    My 2 Cs,

    What you have to ask yourself when deciding whether to go standard, slotted or slotted and drilled is what you will be doing with your car and whether you suffer from brake fade.

    Upgrading the rotor alone will not improve the breaking capacity.

    When a brake starts to overheat (different pads have different operating temps.) it releases gases from the face of the pad where it makes contact with the rotor. This is ones cause of brake fade. The slots acts as wipers or gullies so the gas has a place to escape and prolongs your braking capacity under high loads.

    Another way to tackle fade is to improve cooling. Your stock rotors are already ventilated. This draws air through the middle of the two faces to keep the temps under control.

    To dissipate heat, you need surface area. By drilling holes through the rotor, not only are the gases are released, it also allows the air through the vanes to pass through to the contact face of the rotor to improve the cooling. This is why radiators consist of lots of closely bent fins. It’s all about surface area.
    However, with drilled rotors, due to less “meat” on the surface, their lifespan is limited. Ideal for track work where they are changed and checked regularly.

    If you are looking to increase breaking capacity, you will have to look into upgrading your pads and in some cases, upgrading callipers to suit larger pads and larger diameter rotors.

    I have just recently upgraded to slotted RDAs and QFM pads. My reason is that I was getting shuttering and fading after 4-5 hot laps on the National circuit at QR. I haven’t been back there yet, but with only the brake upgrade alone, I shaved off 3 seconds at Lakeside. Braking capacity have only increased marginally with the new pads, but what the greatest improvement is the confidence it gave me to break a lot later and harder time after time knowing that it will pull up.

    So that’s MY experience with standard Vs slotted rotors. It gave me -3sec and that all I need to justify my purchase.

    Hope this gives paints you a better picture for you to decide which way you want to go.

  8. #28
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    Default Malware identified in included link

    The mazdaspeed link Nuliaj posted has been flagged malware infected by my systems. I have disabled the link, by adding an underscore after http in the URL:

    http_://www.mazdaspeedforums.org/forum/mazdaspeed-3-6-suspension-brakes/1990-crossdrilled-rotors-what-you-should-know-before-buying.html

    If you wish to view it copy paste and then remove the underscore.

    If this is a false alarm I'll remove this notice and restore the link.
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  9. #29
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    Some great info here

    Ok not a brake expert, so can someone then explain why (based on the information in the previous posts) many performance car manufacturers (Porsche etc) and Superbike manufacturers fit slotted/drilled or both types of discs to their hi po machinery?

  10. #30

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    oh..... interesting comments about drilled rotors...... learn something new every day.

  11. #31

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    Quote Originally Posted by shakespeare View Post
    Some great info here

    Ok not a brake expert, so can someone then explain why (based on the information in the previous posts) many performance car manufacturers (Porsche etc) and Superbike manufacturers fit slotted/drilled or both types of discs to their hi po machinery?
    Which would you prefer, cross drilled or standard looking brakes on your million dollar super car? How many of the people who can actually afford these things are actual enthusiats and understand things like brakes? Then there's enthusiats who believe the common myths and this is part of the perpetuating cycle. What makes the supercar brakes so good is the size (as we've been saying all along) and material of the brakes (carbon ceramic). Most of them are running 350mm and bigger discs. This and the brake pads/calipers is what gives them their braking power. Would it suprise you that there have been reports of more than a few new GTRs showing cracked rotors?

    Are there any Benefits?

    The primary benefits of cross drilled rotors are in unsprung weight and rally applications. In a situation where unsprung weight is critical to the performance of the vehicle, xdrilled rotors can shave off ounces of weight to give you an edge over the competition. (Think sport race bikes). In rally applications, the holes allow dirt/water to be pushed through to allow for a clean braking surface.

    Many manufacturers will claim "better pad bite" and "fresh pad surface" as the holes will continuously grate away at the exposed pad surface, preventing glazing. Of course what they fail to mention is that you can get exactly the same effect from a slotted or dimpled rotor.

    Of course, they also look cool, which is the main reason they exist in the first place!


    If This is All true, Why Do Sports Cars Use These Systems?

    Aesthetics and racing pedigree. Bigger wheels, bigger brakes, and lots of holes...these are much more aesthetic modifications then performance minded ones. Larger wheels tend to be heavier (to maintain strength) which increases unsprung weight, which reduces acceleration, handling, and braking ability, while decreasing tire availability (especially in R comps). Some companies actually specialize in making smaller rims for some major performance vehicles, just so the owners don't have to purchase custom tires for their outlandish rim configurations. (Fiske is one of them). The larger rotors tend to have the same negatives, as increased size/mass adds to the unsprung weight increases...which is one of the reasons they get so many holes drilled in them. (Less mass = less weight basically the counter to the increased braking size).

    Larger wheels, larger rotors, and xdrilled holes sure do look cool, but that doesn't mean it’s the best solution. Don't mix aesthetics with performance! You can search most of the manufacturer forums, (like the C6 forums, Porsche and Audi Forums etc) for many examples of rotor failure, cracking, and premature pad wear from this aesthetic bling.
    The comments about gases need to be researched I think. Everything I've read says that modern materials used to make brake pads do not generate gases (or enough) to even be an issue.

    Birdhouse and Jmac, just out of curiousity what size rotors were you running before upgrading in your Skyline/SSS and were they OEM?
    Last edited by Nuliaj; 22-06-2009 at 01:06 AM.
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  12. #32
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    O.K

    So after some reading, It seems as if cross drilled is a definite no go. So still tossing up between the Slotted DBA's or the standard DBA's.

    2 of you have spoken from experience saying that going from OEM to slotted felt a lot better, but they weren't on mps'. From driving the car when it had a good set of brakes and from what ive heard, the MPS has pretty good brakes standard.

    However, would the DBA standard be as good as the standard brakes which come with the 3MPS when new? DBA is a good brand so I assume they would be, if not better.

    I don't experience any brake fade driving how I do, as I don't do any street racing or constant hard cornering, but there is no way im sticking with my machined jelly brakes. So, would the jump between standard DBA and slotted DBA be big enough to warrant getting the slotted? Cost isn't an issue. I guess the only way to know is to try it. When i say "would the jump between standard DBA and slotted DBA" i mean the brake bite of standard compared to slotted, keeping in mind that i don't experience fade.

    I have new pads and brake fluid, as of 2 weeks ago if that matters.

  13. #33
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    45 years in the trade, Auto TAFE teacher for 29 years, race car driver, involved in many forms of motor sport - sort of give me some experience, lol.
    As a teacher I find that if I have to justify my comments, I can, but it would make too long a post.
    Back in the mid sixties we used to drill holes in the disc pads, as well as hacksaw slots in the pads for various reasons, mainly disc pad chatter, The fact of losing friction area is correct, but it is so small a percentage it has no effect. I have fitted hundreds of slotted and cross filled discs and never had a problem. I have only ever heard of one drilled disc shattering and that was on a track car, so I have no real proof. I have seen a few discs with a hair line cracks from one of the drillings, upon Xray it was found to be only a surface heat crack. Heat cracks are fairly common and so fine they mostly dissappear with machining.
    Warped discs are caused by the disc cooling quickly, but the area where the caliper and pads are cools much slower causing the warp. Sometimes can be reversed by getting the brakes hot and then driving without using the brakes thus allowing the disc to cool evenly.
    As for machining discs - a good money spinner for mechanics - but read the workshop manual or manufacturers recommendation on minimum disc thickness. Normal disc wear is usually beyond wear limits. The DBA catalogue has disc specifications listed, listed for a good reason.
    Heres a controversial statement for you - "drum brakes actually stop better than disc brakes" - disc brakes just don't fade with heat as drum brakes do. Drum brakes have a larger surface area and for any single stop are far more efficient. Why do heavy vehicles use drum brakes and downhill roads have signs "trucks use low gear". Before I get too many comments YES some trucks now have discs, but their payload is reduced because of the disc weight.
    Last edited by rd415; 22-06-2009 at 10:17 AM.

  14. #34
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    Quote Originally Posted by tone View Post
    O.K

    So after some reading, It seems as if cross drilled is a definite no go. So still tossing up between the Slotted DBA's or the standard DBA's.

    2 of you have spoken from experience saying that going from OEM to slotted felt a lot better, but they weren't on mps'. From driving the car when it had a good set of brakes and from what ive heard, the MPS has pretty good brakes standard.

    However, would the DBA standard be as good as the standard brakes which come with the 3MPS when new? DBA is a good brand so I assume they would be, if not better.

    I don't experience any brake fade driving how I do, as I don't do any street racing or constant hard cornering, but there is no way im sticking with my machined jelly brakes. So, would the jump between standard DBA and slotted DBA be big enough to warrant getting the slotted? Cost isn't an issue. I guess the only way to know is to try it. When i say "would the jump between standard DBA and slotted DBA" i mean the brake bite of standard compared to slotted, keeping in mind that i don't experience fade.

    I have new pads and brake fluid, as of 2 weeks ago if that matters.
    Mate, Best bet would be to see what the price difference is between the non slotteds and the slotted rotors, then make your choice.


    Nuliaj, I have no idea what the standard sizes were, but upgraded to Ad22vf. http://www.pulsar.org.au/tech_ad22vf.php
    Prior I had the normal GTIR rotors, then upgraded to DBA slotted rotors.
    Last edited by Jmac; 22-06-2009 at 10:22 AM.
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  15. #35
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    [QUOTE3]Mate, Best bet would be to see what the price difference is between the non slotteds and the slotted rotors, then make your choice.[/QUOTE]

    the Standard are A$287 , the slotted pair are A$389 and then their is a slotted pair 4000 series for A$413. the $413 is still $100 less then i was willing to spend so I guess it depends how much I want to make my girlfriend spend. haha

    But yeah, If the brake bite between the slotted and standard is minimal. I guess id just get the standards. As I said, I don't race my car or brake hard constantly.

    btw. Im not sure on the difference between the 4000 series. If i get the slotted id just go the standard slotted i guess

    Ok just got off the phone to DBA. The 4000 series have a hardening coat on them, been painted with a heat absorbing paint which allows for better heat tracking and monitoring when going around the track. Said it would be beneficial if taking it around the track or around the mountains. Probably not that beneficial going the 4000 slotted over standard slotted if your not an aggressive driver or go around the twisties too often.

    He did say the slotted brakes are better for street use as the first 0.3 seconds of braking, you are braking on gas, so the initial bite with slotted is better then standard OEM style brakes because the slots remove the gas.
    Last edited by tone; 22-06-2009 at 10:38 AM.

  16. #36

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    Interesting comment about warped brakes on Commodores. Not that long a go I picked up a rental car from the airport. It had just come off the truck and had 9km on the odo. It also had warped brakes and a pulsing pedal. They obviously have a design and/or production problem.

    Anyway back on topic. Before BBK's were invented I used to fabricate my own brake systems for club racing. I did a lot of experimentation with various different hats, rotor sizes and surfaces. I even got to the stage of developing my own pad material and working with an Australian manufacturer to produce it. Along the way I got a good feel for what works and what doesn't.

    If I were trying to improve braking performance I would proceed in this order:

    1. Chose the appropriate pad material for the application. This may take a bit of experimentation because what works for one car doesn’t always work for another.
    2. Increase the flow of cooling air. Using ducting is not recommended for road cars because cooling ducts are incredibly effective and will over-cool the brakes. However minor improvements can be achieved by using wheels that aid brake cooling.
    3. If fade/warping/cracking continues, install larger rotors that have more mass. This works EVERY time. Calipers are less likely to need attention and usually only become an issue if their design is so poor that they lack rigidity and give a spongy pedal.

    But something that hasn’t come up in this conversation is driving style, which in my view is the greatest contributor to damaged rotors. It’s possible to brake very hard without damaging the rotors, but it’s a learned skill.

    However the MPS doesn't have crap brakes and if you're not tracking the car you'll get as much performance as you need from DBA standard rotors, and you can put the money you save toward other go faster bits. I've been running DBA standard rotors at the front for over 50,000km. No cracks, no warping, better hardness and wear characteristics than OEM rotors. The only time I ever had fade was when I used the wrong pad material.
    Last edited by kmh001; 22-06-2009 at 11:58 AM.

    Gone to Volvo


  17. #37

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    DBA have agood reputation and use good materials.......just go slotted. they look cool!

  18. #38
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    Quote Originally Posted by MaN|aC View Post
    DBA have agood reputation and use good materials.......just go slotted. they look cool!
    I think the mps rims are too spokey to really see the slots through them dont you think?unless they are gold or something

    Is it just me or did streetunit just start selling EBC pads. saw some Red Stuff for 99US each for the fronts. and Green Stuff for 76 each

    sorry for going off topic.

    but yeah, Still pondering.

  19. #39

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    Quote Originally Posted by Nuliaj View Post
    Birdhouse and Jmac, just out of curiousity what size rotors were you running before upgrading in your Skyline/SSS and were they OEM?
    I kept the same size rotors and replaced the plain stock rotors. F 296mm and R 297mm.

    Have a look at the RDA range. They were a bit cheaper then DBA range and i've heard good and bad things about the two. If you're not going to take your car to the track, you may save a few $$ there. I went for the cheaper option and have not had any problems yet.


    I've also upgraded my break lines to braded ones which gave better feel as well. Something else to look into Tone.

  20. #40
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    Hey tone,
    I have just put a set a DBA Slotted with hawk pads on my MPS3, got them from MPS Garage. I reckon they brake better(but that could be just because they're new)and they look pretty good. Have only had them on for 200k so can't say much about pad wear but have had them on my sooby for the last 2 years, after i swapped from stock, and the wear wasn't noticeable different. They're a great quality disc and arn't very expensive, easy to install as well if you have a couple of hours to spare(even tho my mate did it!).

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