Countersteering of Motorcycles & Bicycles

Discussion in 'Physics' started by thingmaker3, Oct 6, 2008.

  1. thingmaker3

    Thread Starter Retired Moderator

    May 16, 2005
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    My wife and I took a beginner's motorcycle class this weekend. One of the concepts taught was "countersteering." The notion is to briefly press the handlebars the wrong way to initiate a lean in the correct direction before using the handlebars to steer. Rephrased: press forward on the left handlebar to initiate leaning into the left turn; press forward on the right handlebar to initiate leaning into the right turn.

    It is counter-intuitive, but it does work. I saw it work and I made it work.

    But how the heck does it work? Why does the bike begin to lean right when the front wheel is moved from in-line to left?
     
  2. Mark44

    Well-Known Member

    Nov 26, 2007
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    I've been riding my "scooter" long enough now that the counter-steering business is subconcious. I think that the reason it works is centrifugal (really, centripetal) force.

    Let's assume you're going down the highway and the road curves to the left. As you enter the curve you pull back just a little on the right handle bar, and push a little on the left handle bar. So even though you're entering a curve that goes to the left, the bike is starting a curve to the right. The bike's center of mass wants to conserve its momentum, and continue in a straight line, which causes the bike to lean to the left. At this point, you can steer into the curve.
    Mark
     
  3. thingmaker3

    Thread Starter Retired Moderator

    May 16, 2005
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    So, the inertia of the bike bike is forward, but the tiny turn from the push changes our reference?
     
  4. Mark44

    Well-Known Member

    Nov 26, 2007
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    I believe so.

    It also seems to me that just leaning the bike in the direction of the curve doesn't cause the bike to turn, but instead keeps the bike from falling over. That is, if you were following the curve to the left, if you didn't lean the bike into the curve, a radial centripetal force toward the right would be acting on the center of mass of the bike. When the bike is leaning to the left, its gravitational force acts straight downward toward a point to the left of the bike's centerline. The radial centripetal force is horizontal and to the right. The resultant of these vectors is a vector from the c.m. of the bike and through the tilted plane of the bike.

    Anyway, I think that's what's happening.
    Mark
     
  5. triggernum5

    Active Member

    May 4, 2008
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    The purpose is to swing the contact patches of the tires out from beneath the center of gravity, thus creating a lean in the desired direction upon steering correction by countering interia's desire to continue in a straight line.. The higher the speed, the more energy is required to initiate the proper lean, and the correction time allows more energy to be transfered through the mass of body/bike.. If you can throw enough weight into your turn you don't need to counter-steer with the handlebars, but with motorcycle weights and velocities, it takes quite a bit of energy to skid the tires out far enough from the center of mass to accomodate a tight turning radius..
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    Lets say the bike is not moving and you hold it as not to fall down with its front wheel in a straight direction. If you release the bike it will fall to the right or to the left depending on which side it is leaning a bit more. Now, if you turn the front wheel to the right, and release the bike it will fall to the left even if it had a small initial lean to the right when you was holding it.

    Below is the explanation:

    Imagine you have a straight line connecting the front and real wheels when the front wheel is facing straight. This line is connected on the center of the axis the wheels spin of. If you hold the front wheel facing straight then the mass of the bike is distributed equally on the left and right side of the imaginary line so if you release the bike it will fall to the side where it was leaning a bit before falling.

    If you turn the front wheel to the right this imaginary line declines to the right because the front wheel axis of rotation moves to the right (remember the line is connected on the center of the axis the wheels rotate). Thus, the center of mass of the bike is no longer distributed equally on the left and right side of the line, there is more weight on the left side of the line, thus a greater force pushes the bike down to the left side than the right, thus it falls to the left.

    The same holds if you turn the wheel to the left and the bike falls to the right.

    If you do it while moving it helps you leaning in the direction you would like because of the above explanation. In other words the mass of the bike helps you to lean.
     
  7. thingmaker3

    Thread Starter Retired Moderator

    May 16, 2005
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    That matches what the instructor drew on the board.

    This is beginning to make sense to me now. Thank you!

    AHA! So countersteering is akin to pulling one of the legs of a tripod in between the other two! Thank you!!
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Here is what happens if you can't lean into the turn.
     
  9. thingmaker3

    Thread Starter Retired Moderator

    May 16, 2005
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    I don't think the Oregon DMV issues driver's license endorsements for for those...
     
  10. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    Do you rely on the state road department to make steep hills
    easy to manage.What about the physics of a heavy machine
    stalling on a hill,do you train for that.
     
  11. Mark44

    Well-Known Member

    Nov 26, 2007
    626
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    No, my bike's 90 horsepower engine makes steep hills easy to manage. The Wa DOT (Dept of Transportation) doesn't have anything to do with it.

    What about the physics of a heavy machine stalling on a hill? I don't ponder the physics of it--I use my eyes to look out for such things.
     
  12. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    If a heavy machine stalls on a steep incline some thing related to
    physics has to happen. In auto racing the cars that get into
    trouble are pulled to the outer wall by force. Race tracks are
    designed by experts in physics .Every thing fails some time.In a
    post someone said computers have more than there share of
    unknown failure.This should not happen in physics,Can the rules of
    physics bend.Do you have an example of physics going wrong
    and self correcting.
     
    Last edited: Oct 9, 2008
  13. Mark44

    Well-Known Member

    Nov 26, 2007
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    This doesn't make any sense to me. As I recall, we were talking about the physics involved in steering a motorcycle around a curve in the road. There wasn't anything about heavy machinery in the road or the rules of physics bending.
    Mark
     
  14. thingmaker3

    Thread Starter Retired Moderator

    May 16, 2005
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    Loosewire, do you refer to a steeply banked curve? If so, the bank helps counter the centripetal influence. This allows the cyclist (or any other vehicle) to safely use the curve at higher velocity.

    Stalling only happens if one is in the wrong gear - not going to happen while going up a hill.
     
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