Head Shake

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by Edder B, Jan 30, 2013.

  1. Edder B

    Edder B Meister Poser

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    Went out riding yesterday. 65 degrees in January, what a great day. Anyway, as I was slowing for a light going around 60 mph I let go of my handle bars and started to get a head shake or slight tank slapper. Tried it again at a lower speed and it did it again. Never noticed it before and I'm wondering if that's normal for the KTM and if not, what would cause it.
    #1
  2. mcmann

    mcmann Motorcycle Maniac

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    Scoot up on the seat and try it . . . . Need some weight up front. Some tires cause head shake on different bikes. Sometimes, raising the forks in the triple clamps will help . . . Puts a little more weight on the front tire. Sometimes, you can rotate the tire on the rim and it may help.

    I had a MT90A front tire that was fine until I swapped it back and forth with a more aggressive tire (TKC80). I developed a slight hands off head shake that I could not get rid of (re-balanced & rotated) . . . Finally, put the TKC80 back on which was fine. The next MT90A had no head-shake????

    Tires and head-shake can be a mistery:huh
    #2
  3. geometrician

    geometrician let's keep going...

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    "decel wobble" is what you're experiencing , as opposed to "accel wobble" where the front end goes light under accleration and the tire skips over imperfections in the pavement. Yes, it is common on the Adv's as well as many other motorcycles.

    Among possible causes are: steering geometry; suspension settings; tire design; tire inflation; tire wear; distribution of rider/passenger/gear.

    Generally speaking the more quick-steering & "nimble" a bike is the more likely decel wobbles occurs as more weight is shifted to the front end.

    One solution is to fit a steering damper, which damps (slows) the oscillations down before peak energies begin to move the front end from side-to-side, which can increase to what is commonly called a "tank-slapper" where the front end goes from full-lock to full-lock. This wave amplification can build quickly on some bikes to the point of the handlebars being torn from your hands which generally ends in a crash. Steering dampers are included on many newer motorcycles (usually sportbikes) and help greatly when riding offroad to prevent the front end from being deflected by rocks, bumps, ruts, etc. Great investment! Personally I am a fan of the Scotts damper though there are several to choose from.

    Here's an example from the Isle Of Man TT races
    <iframe width="640" height="480" src="http://www.youtube.com/embed/LZ1srcQMa_0" frameborder="0" allowfullscreen></iframe>
    #3
  4. v8toilet

    v8toilet Nothing to see here.

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    Suspension setup and tire wear are the usual suspects. The stock scorpions are known offenders. What changes did you make before you noticed the shake? You said you were decelerating which loads the front so adding more weight there is probably not the answer. Did you remove luggage and not adjust the preload?
    #4
  5. BoulderGuy

    BoulderGuy out ridin'....

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    Mine did the same thing with the stock Pirelli front tire. (but has never done it with any other tire) Go figure...
    #5
  6. geometrician

    geometrician let's keep going...

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    Raising the forks tubes in the triples reduces trail & makes the bike MORE sensitive. Trail give self-correcting steering; ie the less trail you have the more chance of the bike shaking the front end.

    You want less weight not more!

    Oh yeah the front Scorpion is bad even when new!
    #6
  7. drued

    drued Adventurer

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    One simple solution is to tighten up the steering head bearings. My '05.5 950, with 90,000 miles, never had head shake while my '12 990, with 11,000 miles, had decel headshake until the bearings were tightened. Now there is no problem.
    #7
  8. bigkuri

    bigkuri Been here a tad bit longer than a while

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    The tyres are the usual thing, and as said Scores can do this even when new! Suspension set up goes a long way, with tons of theories, but I personally found it cured as a side result of putting 0.64 springs in.
    #8
  9. speedy 1

    speedy 1 Wizard

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    as others have stated tires and or wheel balance is an obvious place to look
    also
    don't overlook the rear wheel alignment i.e. make sure it is on track with the front wheel
    if it's out enough it will steer the bike one way while the front wants to go the other setting up an osculation
    #9
  10. Edder B

    Edder B Meister Poser

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    Thanks for all the responses. I did recently put new set of Heidenau Scouts on but I think I need to check the head bearings.
    #10
  11. marin ktm

    marin ktm Been here awhile

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    Me to. I have had 3 Pirelli Scorpions and every one wobbled. I don't buy them any more.
    #11
  12. Misery Goat

    Misery Goat Positating the negative Super Moderator

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    I've run Scorps in the front and didn't have any head shake. Though the few times I did have head shake my preload wasn't set right. :deal
    #12
  13. DirtyADV

    DirtyADV Long timer

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    Scorpion Tire Shake! All I have had have started shaking after some wear:

    <iframe width="640" height="360" src="http://www.youtube.com/embed/uzzqR_iJrUg" frameborder="0" allowfullscreen></iframe>

    Not that badly in this movie have seen worse on previous tires.

    /Johan
    #13
  14. Katoom72

    Katoom72 Been here awhile

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    Exactly what my adv did on stock tires. The Hidenau's go in a perfect straight line.
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  15. 5 speed

    5 speed Been here awhile

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    Not bad at all, I have plenty of bikes that were way worse, road surface the amount of weight transfer on decel, all play a part as well..
    #15
  16. Orangecicle

    Orangecicle On a "Quest"

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    A. Don't take your hands off the bars when slowing down.
    2. Run your hand over the front tire and see if the lugs are cupped. If so, replace.
    iii. Don't buy Scorpions for the front. Try something else that best fits your riding style/habits.
    #16
  17. DesertSurfer

    DesertSurfer Tail sprayin

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    My Scorps sucked from day 1! There are too many fun experiments to be had testing all the better tire options. If your tires are lasting too long, you're not using the bike properly.
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  18. Maoule

    Maoule Been here awhile

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    How'm I gonna check for cupped lugs if I don't take my hand off the bar? And isn't that gonna be kinda dangerous?:eek1:rofl:rofl:rofl
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  19. Zuber

    Zuber Zoob

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    The early Scorp's were very good, all the ones I used from 05-09 were excellent. Then Pirelli moved the mfg. country or changed the process and now about half of them have a tread that that squirms. This little wiggle in the tread will induce handlebar shake. My original tire on the 2010 Adv was bad. Many I've bought since then are bad. The core is straight, but the tread is not laid on correctly, so it creates a tiny torque that initiates this wiggle at the natural frequency.

    Keep your hands on the bars.
    #19
  20. crofrog

    crofrog Long timer

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    What he said. Same thing for the weight transfer sit on the back of the seat.
    #20