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  1. #1
    RoadBikeReview Member
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    How are Avid road and mt disc brakes different?

    I don't get it; the literature says the pull is different, but shouldn't set up be able to account for that? Regardless, I can't get the brakes to set up, so there must be something to it. Could someone please explain it to me - thanks.

    Another thing, there is a bit of a wobble to my rotor, is how tight I have the rotor bolts going to play a roll in the wobble?

    Thanks in advance.

  2. #2
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    The only way to make the two compatible is to use an in-line device that modifies the pull ratio, like a Travel Agent.

    Front:

    Attachment 283371

    Rear:

    Attachment 283372

    I've researched the possibility of changing the internals before, but was never able to get the proper parts through QBP, so SRAM may just not sell them to the general public. The gist of it is that the caliper lever arm doesn't affect the pull ratio, it's the internal cam that changes between the road and mountain versions.

    Rotor Wobble:

    No, tightness of the bolts should not affect the "wobble," because if it goes away when a couple bolts are looser, this means you aren't equally (or properly) torquing all six T25s. Torquing them all down to the listed spec should simply make apparent any inconsistencies in the rotor's true (read: inherent round nature).

    To rectify this in order to run your pads properly close to the rotor, slip on some grease/oil/contaminant free work gloves and go to work on truing the rotor. This is as easy as deflecting the bent section of rotor by a few millimeters, holding for a few seconds, and letting go. Work slowly and focus on one spot at a time, much like truing a wheel. Also keep in mind that once you ride around and brake, you're putting heat into the system which may cause the rotor to attempt to revert back to its original bent state. This just means you're getting closer to a point where the rotor is completely true, so don't freak out! Just do this cycle a few times and your rubbing rotor should be a thing of the past.
    Note: if you don't have gloves to work with, be sure to have a degreaser on hand; the key idea here is that whatever you do to your rotors, they should be free of oil-based contaminants, which includes your skin oil.


    Hope that helps!

  3. #3
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    I was hoping to get to see the attachemnts but the wouldn't open, However if (LIKE ME) you have a disc specific frame you have a challenge to get your STI style levers set up 100% with bb7 MTB discs. In the end i got some of the new shimano 515 calipers. I will see if i can get my Apex brifters to work with the bb7 MTB, but i have the other option now if i cant

  4. #4
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    Oh dear, my apologies to all, RoadBikeReview doesn't like me as much as MTBR. :/

    That being said, I've never personally gotten the long-pull MTN BB7 to work with any drop levers other than Cane Creek's specific long-pull drop levers. However, mechanics I know have had luck with the Travel Agents. Since picture links don't seem to work for me, feel free to Google Image "BB7 Travel Agent" and you'll get hits showing front and rear setups.

  5. #5
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    Thank for the input. Happy 4th.

    How does the internal cam affect the pull ratio? I would think, if the brake pads are dialed in, pull is pull, and I should be able to get the brakes set up the way I want regardless of the the internal cam? Its not like the act of pulling brake cable is a whole lot different between MTB and road brake levers.

  6. #6
    Cranky Old Bastard
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    Quote Originally Posted by RoadLoad View Post
    How does the internal cam affect the pull ratio? I would think, if the brake pads are dialed in, pull is pull, and I should be able to get the brakes set up the way I want regardless of the the internal cam? Its not like the act of pulling brake cable is a whole lot different between MTB and road brake levers.
    Why do you think Avid goes to the trouble to design different cams for the calipers? If they worked the same it would be easier and cheaper to only make one.

    The cam in the road unit moves the pad farther for the same amount of arm movement.
    So if you use mountain calipers with road levers you have to adjust the arm so that the pads are closer to the rotor or you won't get enough travel for full power. When the brake lever is released the pad won't back away as far from the rotor.
    They will work but it is much more likely you'll get rotor drag and noise, especially when you get dirt or mud on the pads or if your rotors get warped.

    TRP just introduced their Spyre dual-piston calipers. With those both pistons move so they should be quieter (less drag) and they say you get 20% better braking because the rotor doesn't have to be bent to be squeezed between the pads. They are making road and mountain models also but I haven't found any for sale yet.
    "When you know absolutely nothing, anyone who knows 1% more than nothing sounds like an expert."

  7. #7
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    Travel agents work fine but are kind of a drag to keep clean. You can find deals on sets of BB7 road calipers. IMO might as well spring for the right set.

  8. #8
    jrm
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    The castings are the same but the innards are different. They are interchangeable though.

    Convert BB7 to BB7 Road

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