1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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  1. #1
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    Disc Rotor replacement

    Both front and rea disc rotors are slightly bent and I want to get new ones. I already took them to the shop and they flattened twice. So I'd rather get new ones than paying for fixing them imperfectly.

    I have no idea what type of disc rotors I have on my bike. Are disc rotors all same size? I just need generic ones that are compatible with mine. My break system is Hayes HMX-2 front/Hayes HMX-2 Mechanical Disc rear brakes if that matters.

    I don't need expensive ones as I keep bending them anyway. Any suggestion?

    Thanks in advance!

  2. #2
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    You need to make sure you get the same size rotor. If its off the shelf bike then you could easily look up the rotor size. I have used different disc rotors without issue, just be careful of any warranty voiding.

    Any idea of how they are getting bent?

    Here are the instructions for installation.

  3. #3
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    In addition to what Abe said, ensure the replacement rotors are the same type (mounting method) as the existing...

    Here's an image I found via google that should help:

    Disc Rotor replacement-20100104_044320_tech_rotor_type.jpg
    Contact information: http://about.me/marpilli

  4. #4
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    Thanks guys. I measured it and it is 160mm 6 bolt. Looking at the photo above, I assume if it's 6 bolt it must be 44mm BCD, whatever it means, right?

  5. #5
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    Quote Originally Posted by Gotchaman View Post
    Thanks guys. I measured it and it is 160mm 6 bolt. Looking at the photo above, I assume if it's 6 bolt it must be 44mm BCD, whatever it means, right?
    You assume correctly.

    BCD = Bolt Circle Diameter.

  6. #6
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    Quote Originally Posted by Abe Froman View Post
    You need to make sure you get the same size rotor. If its off the shelf bike then you could easily look up the rotor size. I have used different disc rotors without issue, just be careful of any warranty voiding.

    Any idea of how they are getting bent?

    Here are the instructions for installation.
    I don't know exacly why they are bend. I fall sometimes but don't remember hitting them on rocks. Maybe falling on the ground bent them a little over time. Both discs are touching the brake pads slightly although it's not that big deal because I can't notice its resistance. But it makes brake lever adjustment difficult. It has to have lots of play in brake lever.

    And thanks for the instruction, that's helpful.
    Last edited by Gotchaman; 07-12-2012 at 05:17 PM.

  7. #7
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    its possible the caliper position is off due to a crash causing the rotors to bend. When you get the new ones check this gap and adjust the caliper mounting accordingly. See step C-14 in the manual.

    May be a good time to replace the pads too in case there is un even wear. Just a thought.

  8. #8
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    Geologist by trade...bicycle mechanic (former) by the grace of God!

    2012 Specialized Stumpy EVO 29 HT

  9. #9
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    Thanks man! Are Alligator Serration rotors reliable? I'm thinking about this Shimano disc: http://amzn.com/B00629OZ6S. But it says "for rasin pad only." I'm not sure if my brake pads are rasin... How do I find it out? My brake set is Hayes MX-2.

  10. #10
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    I'd recommend the Alligators as well. Lightweight, inexpensive and certainly a rotor upgrade.
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  11. #11
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    Quote Originally Posted by pfox90 View Post
    I'd recommend the Alligators as well. Lightweight, inexpensive and certainly a rotor upgrade.
    Cool. Do you recommend round or wavy one? Do they actually make any difference?

  12. #12
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    The wavy ones cool faster.
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  13. #13
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    I just got my first disc brake setup on a bike and right out of the box, the discs were rubbing almost constantly on one side. Then I figured out that I needed to adjust the brakes so the disc was centered in the pads.

    After they were centered, I noticed the discs still had a slight wobble from side to side, but was in between the pads.

    Now, I'm not an expert, but I don't think you're going to get discs to run perfectly straight through the pads. There's a lot of adjustments involved that could affect that wobble. Your disc and brakes, your hub, how your wheel is mounted in the frame, etc.

    I just went on with the fact that it's not possible to be perfect and it works just fine with a slight wobble. Do you have any pictures of how "bent" they are?

  14. #14
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    It's actually really hard to get a rotor to be true ever again. Much easier to buy a replacement.
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  15. #15
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    Quote Originally Posted by miketrains03 View Post
    I just got my first disc brake setup on a bike and right out of the box, the discs were rubbing almost constantly on one side. Then I figured out that I needed to adjust the brakes so the disc was centered in the pads.

    After they were centered, I noticed the discs still had a slight wobble from side to side, but was in between the pads.

    Now, I'm not an expert, but I don't think you're going to get discs to run perfectly straight through the pads. There's a lot of adjustments involved that could affect that wobble. Your disc and brakes, your hub, how your wheel is mounted in the frame, etc.

    I just went on with the fact that it's not possible to be perfect and it works just fine with a slight wobble. Do you have any pictures of how "bent" they are?
    Thanks for your input. I don't have pics of the rotors. They are slightly bent that it's probably not noticeable on pictures. I brought the discs to a shop once to have them flattened but like pfox90 said they aren't perfectly flat. They charged me $10 for the labor per disc. So yeah, I figured it's better to get a new one instead of fixing it.

  16. #16
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    Quote Originally Posted by Gotchaman View Post
    Thanks man! Are Alligator Serration rotors reliable? I'm thinking about this Shimano disc: http://amzn.com/B00629OZ6S. But it says "for rasin pad only." I'm not sure if my brake pads are rasin... How do I find it out? My brake set is Hayes MX-2.
    Stock pads may be either resin / organic or sintered metal. The only way to be sure of having the resin type pads is to buy some. If I were installing rotors which specified only resin pads, I would buy some resin pads to be sure of having the right ones.

    Try Google:

    MX2 and MX3 pads | Hayes Disc Brake

    Hayes MX-2/3/4/Sole Disc Brake Pad Pair

    Alligator Hayes MX-2/Gatorbrake Disc Brake Pads at Price Point

    Oh yeah, take your mitts off the brake levers once in a while. If you ride with the pads touching or if you ride with the brake levers pulled back all the time, you will end up with hot blue warped brake rotors. Just like people who drive their cars down mountain roads and keep the brakes on the entire time. Eventually the brake fluid heats up and boils, then the pedal goes to the floor. At least with mechanical disc brakes, you can't heat the fluid past boiling.
    Last edited by DavyRay; 07-13-2012 at 06:27 PM. Reason: One last thing...

  17. #17
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    Quote Originally Posted by DavyRay View Post
    Stock pads may be either resin / organic or sintered metal. The only way to be sure of having the resin type pads is to buy some. If I were installing rotors which specified only resin pads, I would buy some resin pads to be sure of having the right ones.

    Try Google:

    MX2 and MX3 pads | Hayes Disc Brake

    Hayes MX-2/3/4/Sole Disc Brake Pad Pair

    Alligator Hayes MX-2/Gatorbrake Disc Brake Pads at Price Point

    Oh yeah, take your mitts off the brake levers once in a while. If you ride with the pads touching or if you ride with the brake levers pulled back all the time, you will end up with hot blue warped brake rotors. Just like people who drive their cars down mountain roads and keep the brakes on the entire time. Eventually the brake fluid heats up and boils, then the pedal goes to the floor. At least with mechanical disc brakes, you can't heat the fluid past boiling.
    Thanks man. I think I'm going to get the Alligator rotors and pads.

  18. #18
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    GREAT INFORMATION ON THESE POST THANK YOU! I learned a ton about brake selections!

  19. #19
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    Quote Originally Posted by pfox90 View Post
    It's actually really hard to get a rotor to be true ever again. Much easier to buy a replacement.
    AmenI've tried bending rotors and all is good for a couple rides,.....then that annoying Zinnnnnng.....Zinnnng....Zinnnnnng comes back

  20. #20
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    I figure, it is mechanical brakes? Then the rotors may be bent due to poor adjustment of the pads. The inner (passive) pad should be as close to the rotor as possible, without rubbing, of course. MX-2 has an adjustment bolt on the inner side of caliper. If my memory still serves me, it is Allen 5mm. Turning the bolt clockwise pushes the inner pad closer to the rotor.

  21. #21
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    Quote Originally Posted by Gotchaman View Post
    Thanks man! Are Alligator Serration rotors reliable? I'm thinking about this Shimano disc: http://amzn.com/B00629OZ6S. But it says "for rasin pad only." I'm not sure if my brake pads are rasin... How do I find it out? My brake set is Hayes MX-2.
    Resin = organic. I would just get something like the Alligators; they are fine.
    Geologist by trade...bicycle mechanic (former) by the grace of God!

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