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  1. #1
    BiTurbo 454
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    Slotted/Crossdrilled Rim?

    Hey all! I'm new, so be easy, and if this is in the wrong place, tell me:

    So I was sittin in my garage swapping the race rotors and pads off of my dad's 1999 BMW M3, and I was looking at these rotors, which are cross-drilled AND slotted (as well as cryogenically treated to resist brake-fade), and than I looked at the rims on my bike (baby-blue '04 HARO F4) and found myself wanting to either slot or cross-drill the rim to increase friction against the brake pad surface. Anybody do any experimenting with this type of idea? Just curious to see if anyone has done it, otherwise, i've got myself a saturday project!

    Thanks!


    These are the rotors in case anyone was wondering what I'm talkin about:
    http://www.frozenrotors.com/store/465PSR

  2. #2
    dillyshotback
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    pretty sure those jawns are to increase cooling, not to increase friction. Theoretically, the smoother the surface, the more surface area the better the braking. That is why chrome stops so well under clean, dry conditions. When they get dirty or hot, thats a whole other story. But, not a real big concern with bmx.

  3. #3
    Senior Member eightdip's Avatar
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    Bummer
    Dip me in chocolate and feed me to the Lesbians, eight times because thats my name.

  4. #4
    Why not? EthanYQX's Avatar
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    That's for cooling, not friction. Your rims won't get that hot anyway. However, I know several people who have taken fingertips off by poking at hot brake rotors after a fast rally stage
    "It is not the critic who counts."

  5. #5
    BMX Veteran live4muzic2's Avatar
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    i would not try it. if so, do it on a old rim, then let us know how it works. the tube may pop through the holes also.
    Quote Originally Posted by Dependent View Post
    Lol where would it break... it has the bigger axles...

  6. #6
    BiTurbo 454
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    yeah, i know the holes are for cooling functions, i've been doing SCCA and road rally events since i could drive, lol, but the purpose of the slots is to keep the surface of the brake pad itself clean and at thier peak amount of grip, and it scrapes a minute amount off the pad to do so. this stuff is for brake pads that are hard, and can be resurfaced that easily.

    with bike brakes, at least for most BMX, it's a rubber compound that is effected completely different than automotive brake pads. therefore, slotting, crossdrilling, or the combination of both, would serve a completely different purpose. as the pad rubs across the rim, each slot or hole would act as a ridge, and increase the resistance as it moves along. it would also (as with automotive rotors) keep the face of the pad "fresh" by removing very minute amounts of "stale" pad surface.

    what i plan to do (on an extra rim i have lying around) is to make a slot with a triangular file every inch around the rim. after i've made the slots, i will file the edge leading to the slot (as it would be when it's rotating) to taper down into the slot, making the other edge of the slot slightly taller than it's other, which will cause the pad to "hit" that edge as it is pressing down on the rotating rim. than, instead of drilling all the way through the rim, i'll set up my drill press to only penetrate about half the thickness of the rim's wall, so it will create a cup-shaped depression. i realize that the rubber pad will not be heated the same way an automotive brake pad would, but i just feel like "cross-drilling" it anyways (it'll look wicked either way)

    i'll do this saturday, and possibly post a picture of the end result when i'm done

    after that i'm planning on looking into figuring out some sort of pad that uses a compound similar to that used on higher-performance automotive brake pads (which contain a higher amount of metal than those used on street-based vehicles, and that is also why a car equipped with race pads/rotors squeel when braking at low speeds), because i figure it should provide more friction than a soft rubber. i'll probably steal the pads off the disc brakes that i've got on my pocket-bike

    i'll update when i've done all this, lol

  7. #7
    Why not? EthanYQX's Avatar
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    Quote Originally Posted by sorestgore
    yeah, i know the holes are for cooling functions, i've been doing SCCA and road rally events since i could drive, lol, but the purpose of the slots is to keep the surface of the brake pad itself clean and at thier peak amount of grip, and it scrapes a minute amount off the pad to do so. this stuff is for brake pads that are hard, and can be resurfaced that easily.

    with bike brakes, at least for most BMX, it's a rubber compound that is effected completely different than automotive brake pads. therefore, slotting, crossdrilling, or the combination of both, would serve a completely different purpose. as the pad rubs across the rim, each slot or hole would act as a ridge, and increase the resistance as it moves along. it would also (as with automotive rotors) keep the face of the pad "fresh" by removing very minute amounts of "stale" pad surface.

    what i plan to do (on an extra rim i have lying around) is to make a slot with a triangular file every inch around the rim. after i've made the slots, i will file the edge leading to the slot (as it would be when it's rotating) to taper down into the slot, making the other edge of the slot slightly taller than it's other, which will cause the pad to "hit" that edge as it is pressing down on the rotating rim. than, instead of drilling all the way through the rim, i'll set up my drill press to only penetrate about half the thickness of the rim's wall, so it will create a cup-shaped depression. i realize that the rubber pad will not be heated the same way an automotive brake pad would, but i just feel like "cross-drilling" it anyways (it'll look wicked either way)

    i'll do this saturday, and possibly post a picture of the end result when i'm done

    after that i'm planning on looking into figuring out some sort of pad that uses a compound similar to that used on higher-performance automotive brake pads (which contain a higher amount of metal than those used on street-based vehicles, and that is also why a car equipped with race pads/rotors squeel when braking at low speeds), because i figure it should provide more friction than a soft rubber. i'll probably steal the pads off the disc brakes that i've got on my pocket-bike

    i'll update when i've done all this, lol
    You probably know this if you've really been racing that long, but there's a reason automotive pads and bike pads are different. The automotive pads need to get much hotter to function properly, temperatures that you won't be able to reach on a bike.

    That is why automotive pads use hard compound, where BMX pads use soft compound. The hard compound needs to get much hotter to function froperly.
    "It is not the critic who counts."

  8. #8
    Why not? EthanYQX's Avatar
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    Quote Originally Posted by sorestgore
    yeah, i know the holes are for cooling functions, i've been doing SCCA and road rally events since i could drive, lol, but the purpose of the slots is to keep the surface of the brake pad itself clean and at thier peak amount of grip, and it scrapes a minute amount off the pad to do so. this stuff is for brake pads that are hard, and can be resurfaced that easily.

    with bike brakes, at least for most BMX, it's a rubber compound that is effected completely different than automotive brake pads. therefore, slotting, crossdrilling, or the combination of both, would serve a completely different purpose. as the pad rubs across the rim, each slot or hole would act as a ridge, and increase the resistance as it moves along. it would also (as with automotive rotors) keep the face of the pad "fresh" by removing very minute amounts of "stale" pad surface.

    what i plan to do (on an extra rim i have lying around) is to make a slot with a triangular file every inch around the rim. after i've made the slots, i will file the edge leading to the slot (as it would be when it's rotating) to taper down into the slot, making the other edge of the slot slightly taller than it's other, which will cause the pad to "hit" that edge as it is pressing down on the rotating rim. than, instead of drilling all the way through the rim, i'll set up my drill press to only penetrate about half the thickness of the rim's wall, so it will create a cup-shaped depression. i realize that the rubber pad will not be heated the same way an automotive brake pad would, but i just feel like "cross-drilling" it anyways (it'll look wicked either way)

    i'll do this saturday, and possibly post a picture of the end result when i'm done

    after that i'm planning on looking into figuring out some sort of pad that uses a compound similar to that used on higher-performance automotive brake pads (which contain a higher amount of metal than those used on street-based vehicles, and that is also why a car equipped with race pads/rotors squeel when braking at low speeds), because i figure it should provide more friction than a soft rubber. i'll probably steal the pads off the disc brakes that i've got on my pocket-bike

    i'll update when i've done all this, lol
    So, let me get this straight. You wanna use disc brake pads on rim brakes? Good luck with that
    "It is not the critic who counts."

  9. #9
    Why not? EthanYQX's Avatar
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    And oh, yeah, wait for the rotors on the car to stop glowing red BEFORE you try and grab them. I've made this mistake more than once, let me tell you
    "It is not the critic who counts."

  10. #10
    BiTurbo 454
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    yeah, good call, and that's also why when cars are rolling into the pits after a race event you stay out of their way, because if they apply their brakes while they are still hot they'll fuse right to the pads lol

  11. #11
    Why not? EthanYQX's Avatar
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    And never hose down a hot rotor with cold water.
    "It is not the critic who counts."

  12. #12
    BMX Veteran live4muzic2's Avatar
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    Quote Originally Posted by CrankshaftYQX
    And never hose down a hot rotor with cold water.
    haha, i drove my go kart through a big puddle once after a long ride and the motor craked to peices
    Quote Originally Posted by Dependent View Post
    Lol where would it break... it has the bigger axles...

  13. #13
    Dig. KinetikBiker's Avatar
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    I don't like BMW's.

  14. #14
    BiTurbo 454
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    Quote Originally Posted by KinetikBiker
    I don't like BMW's.
    well, i guess not everyone on here understands what a true race-bred machine is.

    this is a bike forum, don't rip on my preference of cars poopy head

  15. #15
    BiTurbo 454
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    i got scheduled (without my knowledge, pissants) to work saturday and sunday, so i didn't get much time to work on this project... maybe tomorrow (sunday) i'll get to it if i decide to wake up BEFORE noon... which i will do, i've got to go to my girlfreind's basketball regionals game at 11am anyways

  16. #16
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    trials riders do this sometimes. they normally take an anglegrinder to the rim

    ps - the holes and slots aren't for cooling, they're for the other reasons you describe. the ventilation part is for cooling(the clue's in the name)

  17. #17
    \,,/(^_^)\,,/ new_dharma's Avatar
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    Quote Originally Posted by sorestgore
    yeah, i know the holes are for cooling functions, i've been doing SCCA and road rally events since i could drive, lol, but the purpose of the slots is to keep the surface of the brake pad itself clean and at thier peak amount of grip, and it scrapes a minute amount off the pad to do so. this stuff is for brake pads that are hard, and can be resurfaced that easily.
    wrong...wrong...wrong!
    drilled and slotted rotors actually run hotter than a comparable vented rotor...the rotors are used as a heat sink to move the heat created in braking AWAY from the calipers. the more heat that ISN'T moved, the hotted the brake fluid becomes, and as the brake fluid heats up IT becomes less effective. by drilling and slotting the rotor you decrease the amount of metal the rotor has, lowering its mass and creating a smaller heat sink.
    the holes are [were???]to remove gasses from between the pad surface and the rotor surface, which isn't a big deal these days. The pad materials that are used create very little gas anymore (unless you buy VERY CHEAP pads, but then why buy slotted rotors!?!)
    the main reason for the slots are used to remove the glaze on pads (and clean, i guess)...but here again, we have a problem...where does all the material go that's being scraped off? into the holes.

    ok, i'm done for now...
    You know you're getting old when you look at a beautiful 19-year-old girl and you find yourself thinking, "Gee, I wonder what her mother looks like?"

  18. #18
    BiTurbo 454
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    Quote Originally Posted by new_dharma
    wrong...wrong...wrong!
    drilled and slotted rotors actually run hotter than a comparable vented rotor...the rotors are used as a heat sink to move the heat created in braking AWAY from the calipers. the more heat that ISN'T moved, the hotted the brake fluid becomes, and as the brake fluid heats up IT becomes less effective. by drilling and slotting the rotor you decrease the amount of metal the rotor has, lowering its mass and creating a smaller heat sink.
    the holes are [were???]to remove gasses from between the pad surface and the rotor surface, which isn't a big deal these days. The pad materials that are used create very little gas anymore (unless you buy VERY CHEAP pads, but then why buy slotted rotors!?!)
    the main reason for the slots are used to remove the glaze on pads (and clean, i guess)...but here again, we have a problem...where does all the material go that's being scraped off? into the holes.

    ok, i'm done for now...
    and all over your nice shiny rims! lol yeah, ok this thread isn't going the direction i'd hoped, i mean we're arguing about what purpose the slots and holes serve on a CAR, but i'm doing this on my bike, so lets get back to that, anybody done this? somebody a little back mentioned taking an angle grinder to the rim, i figure i'll do that, just clamp the axle in a vice (with wood blocks, i don't want to damage my threads) and have my brother or someone rotate the wheel slowly while i grind (lightly) outward from the center across the rim. i figure i don't really need slots or holes, but it would be beneficial to have a surface that increases the resistance to the pad moving across the surface. i'll update when i can, i've gotta work 4pm to about 10:30ish, so after that i'll be workin all night.

    see ya'll than!

  19. #19
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    After reading all the responses to this post, I still don't know why your going to bother. Your brakes should work fine as they are. If not, there are other issues. And who still uses brakes anyway?

  20. #20
    vegan cyclist
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    I ride bike trials, you can leave the wheel on the bike while grinding it. The problem is that grinds only last a couple days before they go to ****, especially if you are dragging the brake as opposed to "lock/unlock" trials braking. few people grind anymore now that someone figured out scoring works better. Take a utility knife to the rim and make lateral cuts every inch or so.

    I work at a rally prep/service shop. You'd have to be half ******** to grab a brake rotor right after the car pulls in for service, it feels like you are standing in front of an oven when taking wheels off. The frequent uneducated opinion is that slots clean the pads off. Letting the pads get a break "pun intended" from rubbing the already hot rotor reduces friction and heat dramatically. All machining of the rotor, even the reason they are oversized for racing, is for cooling (not braking power). Still, some guys will get the brakes hot enough to melt the pads. If the rotors where solid, they'd warp quick.

    Anyone who's driven a rally car knows that even 4,000$ racing brakes suck. It takes almost all your strength to stop in normal street driving conditions. They get better when they're hot, but not much. It's not like you need all that power on gravel, and left foot braking will destroy anything else.
    http://myspace.com/thedevilmakesthree

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  21. #21
    Why not? EthanYQX's Avatar
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    Quote Originally Posted by onetrack
    I ride bike trials, you can leave the wheel on the bike while grinding it. The problem is that grinds only last a couple days before they go to ****, especially if you are dragging the brake as opposed to "lock/unlock" trials braking. few people grind anymore now that someone figured out scoring works better. Take a utility knife to the rim and make lateral cuts every inch or so.

    I work at a rally prep/service shop. You'd have to be half ******** to grab a brake rotor right after the car pulls in for service, it feels like you are standing in front of an oven when taking wheels off. The frequent uneducated opinion is that slots clean the pads off. Letting the pads get a break "pun intended" from rubbing the already hot rotor reduces friction and heat dramatically. All machining of the rotor, even the reason they are oversized for racing, is for cooling (not braking power). Still, some guys will get the brakes hot enough to melt the pads. If the rotors where solid, they'd warp quick.

    Anyone who's driven a rally car knows that even 4,000$ racing brakes suck. It takes almost all your strength to stop in normal street driving conditions. They get better when they're hot, but not much. It's not like you need all that power on gravel, and left foot braking will destroy anything else.
    We do rally on pavement, you know.
    "It is not the critic who counts."

  22. #22
    vegan cyclist
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    yeah, and with the same brake setup. Tarmac stages are the shiz, so much fun it should be illegal.

    you can buy trials rims that are drilled where the brake track would be if they where meant for rim brakes. Funny to see a thread like this in a bmx forum btw.
    http://myspace.com/thedevilmakesthree

    "There is no such thing as bad weather, people are just soft"

  23. #23
    ride. premiumbmx2005's Avatar
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    i almost want to read all this stuff but then i realized that it doesnt matter.

  24. #24
    BiTurbo 454
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    well, so much for stayin up tonight working on this idea. i get to work at 3:45, lock up my bike to some beefy pipe outside where i work (suspended license, so i ride everywhere i go), and go into work. at about 5pm, i walk outside to have a cigarette, only to see a big beefy pipe, and that's it. bike was ***** stolen, they cut right through the cable i used to lock it up. i'm beyond pissed, that bike is my means of transportation, it's what i do, ya know, I BIKE!!! and some ******* decides to rip it off???? seriously, i am beyond words as to how angry i am. i've filed a police report, given full description, including serial number off the frame, everything, but i just have this horrible feeling that i'll never see my carolina-blue baby again....

  25. #25
    BMX Veteran live4muzic2's Avatar
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    Quote Originally Posted by sorestgore
    well, so much for stayin up tonight working on this idea. i get to work at 3:45, lock up my bike to some beefy pipe outside where i work (suspended license, so i ride everywhere i go), and go into work. at about 5pm, i walk outside to have a cigarette, only to see a big beefy pipe, and that's it. bike was ***** stolen, they cut right through the cable i used to lock it up. i'm beyond pissed, that bike is my means of transportation, it's what i do, ya know, I BIKE!!! and some ******* decides to rip it off???? seriously, i am beyond words as to how angry i am. i've filed a police report, given full description, including serial number off the frame, everything, but i just have this horrible feeling that i'll never see my carolina-blue baby again....
    oh those b****s . that really sucks man and if you lived by me id loan you a bike. actually i could probably make a bike with all my spare parts. but i hope they find that bike. before i got my robinson, it was jacked from the house (inside)and brang back on the doorstep as a frame. i hope they get their bikes all jacked.
    Quote Originally Posted by Dependent View Post
    Lol where would it break... it has the bigger axles...

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