Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 31

Thread: Why Rotor Flex?

  1. #1
    Banned. vantassell's Avatar
    Join Date
    Feb 2006
    Location
    SLC, UT
    Posts
    832
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Why Rotor Flex?

    On my BB7 (road) brakes all the of setup/adjustments guides say to have 2:1 ratio of space on the inboard : outboard side of the rotor. This just seems to be setting up the rotor so it has to flex a ton in order to be fully engaged by both pads.

    I'd think that this much flex is a bad thing, why am I wrong?

  2. #2
    surly old man jgedwa's Avatar
    Join Date
    Sep 2006
    Location
    Carlisle, PA
    My Bikes
    IRO Mark V, Karate Monkey half fat, Trek 620 IGH, Cannondale 26/24 MTB, Amp Research B3, and more.
    Posts
    3,300
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I have wondered about that too, and am curious to see if anyone has any informed ideas about it. I would guess that the flex would not hurt anything, and maybe the constant flexing will help bring any warping into line. Sort of like it gets a constant massage!?!

    On the other hand, the "ton" of flex you are talking about must only be a mm or so.

    jim
    Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
    --------------------------
    SB forever

  3. #3
    Banned. vantassell's Avatar
    Join Date
    Feb 2006
    Location
    SLC, UT
    Posts
    832
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jgedwa View Post

    On the other hand, the "ton" of flex you are talking about must only be a mm or so.
    True, it might not be 'that' much flex. I have a ton of squealing right now (having equal space on both sides) and i'm wondering if having the 2:1 ratio holds the rotor in a way to stop the squeal.

  4. #4
    Senior Member
    Join Date
    Sep 2008
    Location
    Maryland
    Posts
    68
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Because there is more of a gradual application of the brakes, maybe it gives better modulation. Or maybe that's just the illusion of greater modulation. I'm not certain just how much braking force would result from only one pad touching the rotor.

    Anecdotally, it reduces the incidence of howling, especially when my brakes get wet. This is probably because the force on the rotor from the outboard pad prevents the rotor from reaching a resonant frequency when bouncing between the two pads. When the rotor is flexing, there's always one pad to slightly damp the vibration.

    All that being said, I don't really pay a whole lot of attention to the setup instructions. I just back the inboard pad out a notch if it's rainy and my brakes are howling.

  5. #5
    Banned. vantassell's Avatar
    Join Date
    Feb 2006
    Location
    SLC, UT
    Posts
    832
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Alright, when I get home looks like i'm going to try setting these up with the 2:1 ratio. We'll see how it goes.

    Anyone else have any experience/thoughts about the 2:1 gap ratio or 1:1 gap ratio?

  6. #6
    MARGINALS
    Join Date
    Sep 2006
    Location
    San Francisco
    My Bikes
    09 Tarmac Pro SL / Sunday BMX /
    Posts
    420
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I do the same thing when I install these types of brakes on customers bikes. The reason is so that you can then adjust the inboard pad in toward the rotor. By setting it up this way the static inboard pad is adjusted so it is pushed out farther than the outboard pad. This reduces rotor flex because the rotor does not need to move over as far to hit the inboard pad and it reduces the risk of the rotor rubbing on the caliper once the inboard pad wears down a bit.

    discbrake..JPG

  7. #7
    afraid of whales Mr IGH's Avatar
    Join Date
    Apr 2009
    Location
    Front Range, CO
    Posts
    2,672
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    If the pads aren't parallal to the rotor then all bets are off. Before I adjust pad distance I make sure the caliper is set correctly by loosening the caliper bolts and pulling the lever so the pads are tight against the rotor, then tighten the bolts. I don't measure the pad's space, I adjust the inner non-moving pad close but not rubbing. Then I adjust the outer pad to be close. The rotor should flex slightly when the brake is applied.

  8. #8
    Senior Member
    Join Date
    May 2004
    Location
    Wilmington, DE
    My Bikes
    2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
    Posts
    8,851
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by vantassell View Post
    Alright, when I get home looks like i'm going to try setting these up with the 2:1 ratio. We'll see how it goes.

    Anyone else have any experience/thoughts about the 2:1 gap ratio or 1:1 gap ratio?
    Look at Ingleside's illustration. That's what Avid is recommending, a pad to caliper gap ratio of 2:1, not a pad to rotor gap ratio of 2:1. I have about 4000 miles on my BB7 road brake (front only) and I can assure you that your braking will feel substantially better using as small of a 1:1 ratio gap from pads to rotor as possible. I just readjusted mine last night to tighten up the gaps and braking is so much smoother and the squeal under heavy braking is gone as well.

  9. #9
    Banned. vantassell's Avatar
    Join Date
    Feb 2006
    Location
    SLC, UT
    Posts
    832
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    If it's supposed to be like Ingleside's illustration, why does Park show it with 2:1 gap?



    I was reading a bunch of threads on mtbr and a bunch of guys there were saying to leave the pads adjusted well, but with light scraping. After a couple of weeks the pads won't scrap anymore, so it'll be perfect.

  10. #10
    Spinning @ 33 RPM Glynis27's Avatar
    Join Date
    Aug 2007
    Location
    NE Ohio
    My Bikes
    '89 Fuji Saratoga, '97 Schwinn Mesa SS, '07 Felt F1X, '10 Transition TransAM, '11 Soma Analog SS
    Posts
    747
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Ingleside View Post
    This shows it perfectly. Do this.
    1989 Fuji Saratoga
    1997 Schwinn Mesa SS
    2007 Felt F1X
    2008 Transition Vagrant SOLD!
    2010 Transition TransAM
    2011 Soma Analog SS

  11. #11
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    The flexing rotor is simply part of the design due to the static pad, nothing to worry about. Been using BBDB/BB7 brakes for 10 years, too. You can use varying distance of the inboard pad to the rotor to tune the brake feel/modulation to your liking. The outboard pad recesses into the caliper, so you're not actually centering the rotor between the pads per se, the 2:1 ratio just optimizes the position of the rotor relative to the caliper body. Avid's recommendation, Park's instructions and Ingleside's illustration all suggest the same thing in any case.
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  12. #12
    Senior Member
    Join Date
    May 2004
    Location
    Wilmington, DE
    My Bikes
    2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
    Posts
    8,851
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by vantassell View Post
    If it's supposed to be like Ingleside's illustration, why does Park show it with 2:1 gap?
    They are showing the caliper to rotor gap, which is what I was confusingly referring to when I said pad to caliper gap. The premise is the same; you want the outer pad extended two times more than the inner pad which requires the caliper to be offset relative to the rotor. When you set the pads gaps to the rotor, you set them as close as possible and even so rotor flex is minimized.

  13. #13
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by joejack951 View Post
    When you set the pads gaps to the rotor, you set them as close as possible and even so rotor flex is minimized.
    Not necessarily. I don't.
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  14. #14
    Senior Member
    Join Date
    May 2004
    Location
    Wilmington, DE
    My Bikes
    2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
    Posts
    8,851
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bikinfool View Post
    Not necessarily. I don't.
    Interesting. What have you found with regards to using offset pads, i.e. what works nicely and what doesn't?

  15. #15
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by joejack951 View Post
    Interesting. What have you found with regards to using offset pads, i.e. what works nicely and what doesn't?
    What do you mean by offset pads? Do I have the inboard pad further from the rotor at rest than the outboard pad? Maybe by a bit (and had to go look at a few as I usually don't even think about it that way). I don't like my brakes to engage right away or have an off/on feel, either, so both pads are dialed back a bit from being as close as possible to the rotor and I don't know if I could measure how much flex I'm getting. I also use the lever's leverage adjustment to fine tune feel, and feel is what I use more than a particular number of clicks or a set distance for the pads. I'm going on about mountain versions rather than road, too.

    Oh, and I never center my calipers on these brakes using Mr IGH's method (do on my Elixir CRs, though).
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  16. #16
    Senior Member
    Join Date
    May 2004
    Location
    Wilmington, DE
    My Bikes
    2003 Specialized Hardrock, 2004 LOOK KG386i, 2005 Iron Horse Warrior Expert, 2009 Pedal Force CX1
    Posts
    8,851
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bikinfool View Post
    What do you mean by offset pads? Do I have the inboard pad further from the rotor at rest than the outboard pad? Maybe by a bit (and had to go look at a few as I usually don't even think about it that way). I don't like my brakes to engage right away or have an off/on feel, either, so both pads are dialed back a bit from being as close as possible to the rotor and I don't know if I could measure how much flex I'm getting. I also use the lever's leverage adjustment to fine tune feel, and feel is what I use more than a particular number of clicks or a set distance for the pads. I'm going on about mountain versions rather than road, too.
    I was apparently confused by your post. I understand now. With the road version of the BB7's, I find that unless I have the pads set as close as possible to the rotor that I get unreasonably long lever travel before the brake really engages. Also, because only the outboard pad moves, I find that a lot of clearance to the inner pads causes a pulsing feeling when braking and extra squeal especially when wet. I've heard other people comment on the lever travel issue when using the road BB7 so it likely is totally different when using the MTB version.

    Quote Originally Posted by bikinfool View Post
    Oh, and I never center my calipers on these brakes using Mr IGH's method (do on my Elixir CRs, though).
    That method is unnecessary with BB7s which allow you to dial in both pads with the adjusters. The cheaper Hayes brakes on my MTB only a dial adjustment for the inner pad so to align the rotor you are forced to use the brake lever to clamp the caliper to the rotor. The outer pad's gap to the rotor is adjusted by cable tension (unlike the Avid's where they specifically warn not to adjust the outer pad position using cable tension). Both systems work but the BB7's are a bit easier to adjust.

  17. #17
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I haven't tried the road versions, but even then from what I've read on the forums the typical road levers don't seem to marry up all that well either. Curious, are there any road levers have adjustable leverage? I had to reread the OP before it sunk in about the road version, thus my mentioning it. The BB7 is the only mechanical disc I'd consider using, I actually favor them over the Elixirs for the most part due to their ability to be easily setup just the way I like.
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  18. #18
    Senior Member
    Join Date
    Sep 2007
    Location
    Gaseous Cloud around Uranus
    Posts
    3,481
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    Unless you have dual piston calipers,you have a primary pad and a secondary pad with sliding calipers.Thus the different pad settings,to combat rotor flex.
    Everything should be as simple as possible...But not more so.---Albert Einstein

  19. #19
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    What do sliding calipers have to do with any of this?
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  20. #20
    afraid of whales Mr IGH's Avatar
    Join Date
    Apr 2009
    Location
    Front Range, CO
    Posts
    2,672
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bikinfool View Post
    Oh, and I never center my calipers on these brakes using Mr IGH's method (do on my Elixir CRs, though).
    Quote Originally Posted by joejack951 View Post
    ...That method is unnecessary with BB7s which allow you to dial in both pads with the adjusters.....
    I do the technique when installing new pads and when the caliper gets knocked on a rock (when mountain biking). It is better way to get the pads parallel when the pads are out of line with the rotor, the other option is to use the brakes and grind the pads back to parallel (with all the squeaks).

  21. #21
    Banned. vantassell's Avatar
    Join Date
    Feb 2006
    Location
    SLC, UT
    Posts
    832
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Just an update, I followed the park instructions for setting the pads and now have significantly less lever throw to engage the brakes (I like less throw). They are still super loud, but they seemed to get better today on the ride to work.

    I'm still am very interested by what everyone is saying, i'm a disc noob. I'm not saying that the park method is right, but i liked the decreased throw it afforded me. I'll post here if the squeal goes away, but for now it's still a work in progress.

  22. #22
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Mr IGH View Post
    I do the technique when installing new pads and when the caliper gets knocked on a rock (when mountain biking). It is better way to get the pads parallel when the pads are out of line with the rotor, the other option is to use the brakes and grind the pads back to parallel (with all the squeaks).
    Huh? Just dial the pads in like in the setup instructions. You knock your calipers on rocks a lot? The CPS washers don't always get everything nice and parallel alone, but that's what they're there for; I still wouldn't use the squeeze the lever method on the BB7s...how do you set your inboard pad for this "method"?
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  23. #23
    I have senior moments... bikinfool's Avatar
    Join Date
    Oct 2008
    Location
    Woodside, CA
    My Bikes
    Many
    Posts
    2,153
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by vantassell View Post
    Just an update, I followed the park instructions for setting the pads and now have significantly less lever throw to engage the brakes (I like less throw). They are still super loud, but they seemed to get better today on the ride to work.

    I'm still am very interested by what everyone is saying, i'm a disc noob. I'm not saying that the park method is right, but i liked the decreased throw it afforded me. I'll post here if the squeal goes away, but for now it's still a work in progress.
    Squealing is more likely from contamination of the pads/rotor, an untrue rotor (easily trued btw) or you didn't get the pads setup as well (square to the rotor essentially) as you think...the CPS system doesn't solve all setup issues, either. Some bikes/forks also can accentuate harmonics from the brakes. Lots of people complain about Avid hydraulic brake noises particularly but personally I think it's mostly in their initial setup, and somewhat that they're a very popular brand (thus more complaints). You might venture over to the brake forum on mtbr, too; here's a link to their disc brake faq for those new to discs http://www.mtbr.com/discbrakesfaqcrx.aspx
    suum quique
    Mountain bikes: Santa Cruz Hecklers (99, 02, 07), Santa Cruz Nomad, Moots YBB, Trek OCLV Pro Issue, American Breezer
    Road bikes: TST, Trek 2300 (Carbon/Alum)

  24. #24
    Senior Member DannoXYZ's Avatar
    Join Date
    Jul 2005
    Location
    Saratoga, CA
    Posts
    11,507
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I find it interesting to see how bicycle disc brakes are going through the same evolution as motorcycles, but 30-years later (same as cars 60-years earlier). We start out with fixed-rotor/fixed-caliper single-piston brakes that eventually evolve into floating-rotor/fixed-caliper dual-piston brakes in the end. The floating-rotor does away with a lot of the squealing, shuttering and uneven wear issues as the rotor will self-centre between the pads.

    I kind of object to the Park tool site's procedure since it does make the rotor flex more than necessary. There is really no relationship 1:1, 1:2, 2:1 between the two sides that makes sense because they're really not related. What I like to do is:

    1. set fixed/stationary pad 1-2 clicks out from where you can hear it rubbing the rotor (this setting is fixed regardless of spacing on other side)
    2. set moving pad as may clicks out as necessary to give you the lever-throw before engagement you desire.

    This minimizes the amount the rotor flexes and leads to flatter contact between the rotors and pads. I like this procedure here: http://www.twowheelblogs.com/avid-bb...set-and-tuning

  25. #25
    afraid of whales Mr IGH's Avatar
    Join Date
    Apr 2009
    Location
    Front Range, CO
    Posts
    2,672
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bikinfool View Post
    Huh? Just dial the pads in like in the setup instructions. You knock your calipers on rocks a lot? The CPS washers don't always get everything nice and parallel alone, but that's what they're there for; I still wouldn't use the squeeze the lever method on the BB7s...how do you set your inboard pad for this "method"?
    Gee, Dude, you make things hard. If the pads aren't parallel, they squeal like a pig until the rotors grind them parallel. While they're getting ground down, there's less sweep area and braking suffers. If you're riding home on a paved rode in the sun, it's not an issue, ignore what I posted and go on your happy way. Yes, between my two sons and myself, we do have rock strikes on our frt calipers, it does happen often enough to need a solution. We also use up pads, sorry, perhaps we're riding too hard for you...I make sure the pad's are not stuck at the limit, after making the pads parallel, then I tweak the clearence.

    Quote Originally Posted by bikinfool View Post
    Squealing is more likely...you didn't get the pads setup as well (square to the rotor essentially) as you think...

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •