675.cc • Triumph 675 Forum

Why do racers stick out their inside knee?

Discussion in 'Riding Tips' started by Craig, Oct 29, 2007.

  1. Craig

    Craig

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    It lets the bike lean less for a given speed. By sliding off the inside of the
    seat, the rider's body weight is moved towards the inside of the corner. This
    means the bike needs less lean for a given speed and turn radius. As ground
    clearance is often the limiting factor in cornering (particularly at higher
    speed) this allows the rider to corner at higher speeds.

    Here's some nerd info that describes turning geometry:

    t= arctan [ v^2/(g*R) ]

    v is your velocity, R is the radius of your turn, g is the gravitational constant.
    t is the "lean angle."It's the angle between

    1. the horizontal, and
    2. a line from the contact patch of your tires through the center of
    gravity of the bike-rider system.

    Hanging off and sticking out your knee moves the CG of the system to the
    inside, while leaving the bike more upright, so you don't run out of ground
    clearance.

    Aside from running out of ground clearance, a second limiting effect is
    caused by excessive lean. At lean angles below 45 degrees from the
    horizontal, tires no longer purely roll and are rotating more about a vertical
    axis rather than a horizontal one. This makes them act more like a rotary
    brush of a street sweeper than a rolling wheel. With steep lean, the contact
    patch twists in place scrubbing away traction and power so that leaning
    farther reduces cornering ability and ultimately causes a washout in the turn.
    Incidentally, since cars do not lean, they do not exhibit this behaviour, and
    can corner with greater G-forces than motos.

    Some riders like to 'feel' the road so they know their lean angle. (You can't afford to look down). It doesn't hurt - they wear pucks on their knees to
    avoid damage. Only problem sometimes is the rumble strips on car circuits.

    Top riders can use their knee to change the balance of the bike, for example
    taking some of the weight off the rear wheel when they want to induce a bit
    more slip.

    Some will claim it also aids braking (because of air drag) going into a
    corner. Every little bit helps....

    Credits: (Thanks to Duncan Hardy ([email protected]) for the bulk of this answer,
    and to Jobst Brandt ([email protected]) for the effect lean has on the tire
    performance.

    Source: http://www.uponone.com - Become A Roadracer Guide (PDF)
     
  2. Stu

    Stu

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    Thanks for the info, now how do I get my knee down :D
     
  3. Daytonadave

    Daytonadave

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    only time i get my knee down is when i secure the anchor lock :lol:
     
  4. DANO

    DANO

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    Like this...........


    ai92.photobucket.com_albums_l3_FDNYDANO18_TPM_0269.jpg
    ;)
     
  5. Craig

    Craig

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    Nice, if only I could make it look so smooth :p got the theory behind me it's just doing it :)
     
  6. SV_Justin

    SV_Justin

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    Thanks for that Craig. Some of us are already professionals!! hahaha

    [​IMG]
    Wheelies on the other hand, they're slighty trickier! ;)
     
  7. Craig

    Craig

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    Impressed, good action shot photo; did it take long to master on the roundabout? :)
     
  8. SV_Justin

    SV_Justin

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    About 45 minutes attacking a smooth quiet roundabout and I was scraping away!
     
  9. Now I find it the other way round :?
     
  10. Keith Code has a section about knee out/hanging off in his Twist of the Wrist books.

    As well as the science/equation bit, which is exactly why riders do this, he suggests there is also a confidence aspect to it. By sticking you knee out it is like pointing which way you want the bike to turn....much like looking where you want to turn....and also if you are able to get your knee down then it gives you that feeling off safety (a little weird!) as you know exactly where the road is and how far you are going to fall should you come off....you will slide along the road form this position rather than fall and bounce!

    Hope this adds another aspect to the answer above!
     
  11. Coz it would look bloody funny if they stuck out their outside knee :D

    [​IMG]

    Taken at Buell Performance Academy Castle Combe 20May09
     
  12. spike

    spike

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    i would like to see you try that on a set of corsas on a cold and rainy day :shock: :shock: ;) :D :D :D :D :D :D :D :?
     
  13. I bet they would do it :D
     
  14. Show offs ;) ;) ;) ;) ;)

    Just cause some of us can't do it - yet :lol:
     
  15. Didn't you see the Motogp from Le Mans on Sunday?

    They went faster in the wet (even on 125's,) than I would dare to go in the dry lol.....
     
  16. Getting Knee down.. My Mate learnt me by going round n round a round abo, i know its cheating but it gets u started..

    In 2nd/3rd, gear sole of foot on the outside of peg pointing towards the deck, get ya arse cheek right on the side of seat n lean like fuck! lol

    Gather ya Balls together n gradully pick up speed as u go round n round leaning more n more!!

    I found it easier wit someone watching u go round giving u indication how close u r t floor..

    Then when u nearly there pick up LIL speed n pick ur spot on the road where u wanna scrape the deck wit ya slider, then again gradually keep going!! I found once i got my knee down it improved my riding SOO Much on the twisty roads cos know how far can push the bike now.. Heres my video of my first time!! :)

    3/4 time round i did full 360o round the roundabout!!

    Hope this makes sense.. enjoy lol :)


    http://www.youtube.com/watch?v=PTEzEJ9aHlg
     
  17. SV_Justin

    SV_Justin

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    Thats the way to learn it, I did pretty much the same
     
  18. D41

    D41

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    I need a roundabout!! :cry:
     
  19. SV_Justin

    SV_Justin

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    Roundabouts + USA = Chaos!!!!!
     

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