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B Forces at rear brake caliper of motorcycle

  1. Sep 11, 2016 #1

    jcw

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    Looking for some help with a rear brake caliper design.

    The rear caliper bolts to a carrier that slides onto and rotates around an axle. An torque arm (motorcycle term) or brake stay is required to prevent the caliper from rotating when the rear brake is applied.

    I have to figure a way to fabricate a brake stay and was trying to determine the forces involved and whether mounting the brake stay as far from the axle as possible is better than closer to the axle. I mean does the force on the bolts holding the brake stay in place increase as the distance from the axle decreases.

    torque arm.jpg

    Thanks in advance!
     
  2. jcsd
  3. Sep 11, 2016 #2

    Merlin3189

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    Gold Member

    So, how would you push something to stop it rotating?
    Say, for eg, I held a stick out horizontally and tried to turn on the spot, rotating about my vertical axis. To stop me you would push the stick in the opposite direction. For most effect, where would you push on the stick? At the end, in the middle, near where I'm holding it?
    In what direction would you push? Like, at 45o to the stick, perpendicular to the stick, parallel to the stick, etc.? (Rough estimates will do.)

    If that tells you the optimum way to push, presumably any other way is less effective and requires more force, which has to be provided by the mounting bolt.

    Edit: PS there may be another consideration - the bending of the trailing arm.
     
  4. Sep 11, 2016 #3

    jcw

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    Thanks. I knew that was probably the answer but I wanted to make sure I wasn't completely off base.
    Modern motorbikes instead of a long torque arm use a tab on the swingarm that fits in a slot on the brake stay.

    http://burntrubber-burntrubbermotor.netdna-ssl.com/21100-large_default/kawasaki-zx10r-rear-brake-caliper-bracket.jpg [Broken]

    This is a picture of what I'm having to adapt to an older motorbike that previously used a long plate or torque arm.

    I'm thinking the length of the torque arm doesn't matter as long as the angle of the arm to the mounting point and axle is the same.
    And taken to the extreme, a simple tab on the swingarm is the same.
     
    Last edited by a moderator: May 8, 2017
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