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Question about motorcycle emergency braking

  1. Sep 12, 2013 #1
    Hello,

    I don't know if this is the right place to ask this, but here it is:

    Does the brake pad/rotor temp effect the stopping distance at an emergency brake scenario on a motorcycle ?

    Assumptions;
    1) there is enough of traction between the tire and the asphalt
    2) a performance motorcycle loops itself over the front wheel under extreme use of front brake
    3) in this emergency brake, only the front brake of the performance motorcycle is used, and it is used just enough to lift the rear wheel off the ground, but not to loop the bike.

    Edit:
    4) All performed in a track
    5) The temp of rotor and pads are always within the range of operating temps
     
    Last edited: Sep 12, 2013
  2. jcsd
  3. Sep 12, 2013 #2

    UltrafastPED

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    Stopping requires that you reduce your kinetic energy - where the rubber meets the road is the only help you have in standard road vehicle design. The purpose of your brakes is to change the frictional mode from "rolling" to "kinetic", and then hopefully to "static".

    Introducing spin/rotation into the question only invites accidents with possibly fatal results for the driver and innocent passers by.
     
  4. Sep 12, 2013 #3

    rcgldr

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    The pads and rotors meant for a street legal motorcycle should be able to provide maximum braking force even when cold. Some pads and/or rotors could get too hot from repeated usage in racing like conditions, but the pads and rotors used on most sport bikes won't have this issue.
     
  5. Sep 12, 2013 #4
    I edited the assumptions.

    More specifically, I would like to know, if my motorcycle would in theory come to stop at precisely the same distance with pads/rotors at 10c vs at 200c, while all other conditions are constant including tire/road and air temps.
     
  6. Sep 12, 2013 #5

    UltrafastPED

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    That is a very large temperature change ... and yes, it would increase your stopping distance.

    Read about brake fade here: http://en.wikipedia.org/wiki/Brake_fade
     
  7. Sep 12, 2013 #6
    Could you elaborate ?

    Why does it change the stopping distance if at either one of the temps, my brakes are still at full force and lift my rear wheel off the ground ?
     
  8. Sep 12, 2013 #7

    rcgldr

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    In this case the braking distance would be the same.

    A difference would occur if the coefficient of friction between the brake pads and rotors were reduced enough by temperature that they could no longer provide enough torque to lift the rear wheel even with maximum force applied to the front brake lever. Read the wiki aricle mentioned above about brake fade. Some braking materials, like carbon fiber, don't brake as well if they are too cold.
     
  9. Sep 12, 2013 #8
    The reason I posted this question is bec I believe the opposite.

    Reason - because a motorcycle doesn't come to full braking power at an instant (in our example it's the rear wheel off state), the temp of rotors and pads will effect the graph of decel UNTIL to the point where the rear wheel is off.

    Am I wrong to think this ?
     
    Last edited: Sep 12, 2013
  10. Sep 12, 2013 #9

    CWatters

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    Working brakes cannot exert more torque than is required to flip the bike (because the bike will flip!). So in effect that sets a limit... As long as they still work well enough to lift the rear wheel then they won't limit braking.

    On the other hand if they have faded to the point where they can't lift the rear wheel any more then how much braking you have will depend on the state of the brakes.
     
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