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death wobbles/tank slapper under compression braking???

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by papermate, Jan 23, 2008.

  1. hi. i ride a new kwaka zx6r.

    the last 2 days something wierd has been happening that i havent experienced before.

    the problem is that after medium to full acceleration rate i change up to 4th gear reaching approx 80- 90kmph. i then took both hands off the bars, and therefore the throttle and leaned back and stretched. (i was tired and the lights were going red)

    however upon sudden releasing of the throttle the bike will slow down, obviously, however the handlebars start to perform a tank slapper. the bike holds it self, and i start to grab the bars again, to stop the tank slapper and let the bike slow down.

    it doesnt really happen at lower gears and lower speeds around 50-60kmph and it doesnt really happen at higher speeds such as 100 - 140kmph.

    i repeated the method though, just to see if it was right. at first i thought that it was

    1. bumpy road
    2. leaning bike
    3. my imagination.

    however, i dont think it is.

    do i have a bent wheel? or is my front wheel out of alignment. can it be?

    or is this just a natural phenonmena of physics with engine compression braking and forces being applied to the front wheel under deacceletartion.

    the reason im concerned is that i havent really changed my riding style, im sure ive done this before and not had the reaction, but im also sure that i have not hit anything that may have mechanincal cause this

    does anyone have anyone experience?
  2. My zzr250 used to shake minorly when you took your hands off the bars and leaned back. My front forks had new forks and oil, steering head bearings were changed and new tyres were put on, both making alot more stable.

    If you go on bumpy roads its possible for the alignment weight do-hickeys to fly off. Also, uneven tyre wear / scolloping of the tyres can cause it to be less stable.
  3. Front tyre and or head stem bearings are fagged out :)
  4. Most of my bikes have done this to a greater or lesser extent (not that that's a recommendation), although it's never been so much as to be dangerous.

    If it hasn't done it before, my first actions would be to check the tyre pressure and, if that's OK, get the wheel balanced by someone who knows what they're doing.

    In fact I'd get both wheels balanced.

    Then you're into things like wheel bearings and head bearings. Not to mention the swingarm bearings and maybe the shock linkages. It's worth remembering that front end antics can just as easily stem from rear end problems.

  5. uh.. in english please? lol
  6. Check your tyre pressures.
    Thats what bob was telling you.
    I would also check your Rear tyre pressure as this can cause bar wobbles if it was under deceleration.
    My bet is your tyre pressures are low.
    As for head stem bearings thats the bearings that sit on top of the forks in the yoke between the hadlebars.
  7. He's saying your front tyre has uneven wear and is causing the wobble, or that your steering head bearings need replacing.
  8. The main thing is that, under braking or deceleration, the steering head angle steepens and there is less castor (self-centering) effect on the front wheel.

    It is a common issue. The causes can be (but are probably not limited to):

    1) Removing both hands from handlebars - not advisable (seriously!)

    2) Loose or worn steering head bearings

    3) Loose or worn swing arm bushes

    4) Incorrect tyre pressures.

    5) Worn tyres

    6) Incorrect tyres fitted

    7) Too much compression damping or too little rebound damping, esp on the front.

    Is the problem still very noticeable with one hand still on the bars?

    Have you dropped the forks a little through the triple clamps recently?

    The effect can be noticeable at just certain speeds - as you have found out. That is because the harmonic reaction which occurs is triggered by something, and magnified, at a particular rate.

    A steering damper should help to control it, but changing tyre pressures (always check them cold with a pencil-type gauge) could move the speed at which the problem comes and goes. That's a good way to get an idea of the origin of the problem.

    All the best

    Trevor G
  9. Papermate, Bob DID use english.

    What tyres are on the bike? Are they worn? Some worn tread patterns can induce the wobbles of which you speak. (Mich Pilot Sports, when fagged/worn, were a classic for inducing a wobble when hands were not on the bars)

    In regards to the head stem bearing, jack the front wheel off the deck just a little **, and turn the handle bar slowly from full lock to full lock, feeling for any notches - any roughness suggests head stem bearing is worn. Or, if you hear a knock from the front under hard braking, then that's a sign too.

    **No responsibility or liability is assumed if the bike falls over performing this manouver.

    Seems as TG has given you a bunch more things to consider.
  10. hmm..... thanks.

    all makes sense. the problem is SLIGHTLY noticable with hands on the handlebars.

    it may be tire pressure, i can only assume this is the most probably although i had the 1000km ....well... 1000km ago. i will check my manual, but what should

    1. front pressure be?
    2. rear pressure.

    i doubt that any other componants are worn or damaged. i only have about 2500km on the clock and havent done any extraordinary riding. long trips, pushed hard at times, but nothing extraordinary the bike isnt capable of.
  11. :?

    You ride a brandnew 6R and don't have basic maintenance concepts under your grasp?? :? :-k

    Tyre pressure is not something left to the scheduled service. :facepalm:
  12. Well on a bike that new, tyre pressures have to be No 1 suspect.

    They'll change depending on ambient air temperature. Were they last checked when it was 40 deg C and the weather's now cooled off?

    Check 'em now. Bet they're 5 psi low.
  13. apologies, i dont mean to sound ingnorant, these are not terms ive learnt before.

    no, tires are not worn, i have inspected for uneven wear and there are no indications.

    look - im not a mechanical dummy. my previous zx2r had many issues and learning points, and i did a few minor maintenance things on it such as chain, speedo, lights etc, but this is the 2 month of my new zx6r. in terms of tire pressure maintenance as i mentioned there has not been excessive, or extraordinary riding since the 1000km service, so no reason to assume that it would be an issue. as mentioned i noticed a performance change in the last 48 hours and am enquirying about possibilities.

    so forgive me if i sound arrogant in saying that my questions are fair questions as im concerned about riding habit or potention issues that may occur due faulty parts or treatment of the bike.

    besides tire pressure maintaince, what other concepts are feasible for me to maintain in between schedule regular services?
  14. General safety inspections. Your manual will have a list of things you should check before you ride. I don't know anyone who actually does all these preride checks, I certainly dont. They're checks like tyre pressure, brake pads, coolant levels, headlights + indicators + brake lights working, etc.

    Anything else is scheduled servicing unless you do it yourself - in which case oil every (insert your opinion here, I try to change oil every 4000).
  15. Sorry dude, I'm not taking an attitude to you, but if you're in Victoria, you have ridden around on a 250, possibly the ZX2R, for at least 15months - with all the maintenance that implies, and you have had a BRAND NEW bike for TWO WHOLE MONTHS, ridden 2500km and you still haven't opened the manual to suss out the most basic aspects of looking after your very valued possession...


    Sorry mate... I'm simply amazed.

    'nuff said.

    Go through Trevor's list, then get back to us.
  16. firstly, trevor thanks for the list. most helpful post.

    secondly, i would like to bite my tounge but i just cant do it.

    robslave your bit of a nob head. you have this preconceived notion that i am a showpony who has bought at flashy bike without any of the values or passions that you posses riding/race bikes. you qualify your statements by claiming your not giving me attitude but you'd be lying to say you weren't. im not going to argue i bought the 6r because i think it looked great, and im not going to begin to argue that i may be a better rider that you. un-productive twit you can be, with a chip on your shoulder + a point to prove that your knowledge, standpoint and passion should be a benchmark as to why someone owns a motorcycle. just because of the fact i own a new bike and are asking questions should be enough to allow me leniency even if i have overlooked items in the manual or not aware of what you call basic maintenance concepts. i wouldn't be surprised if you use preconveinced notions in other aspects of life which would warrant you being a twat in your conversation more than once.

    i read the manual.

    i talk and ask about technical things when im not sure.

    however without a a full range of tools or a workshop there is limitations to the maintenance i can do. What else than look at the tire pressure and check my fluids, chain and instrument function can i do on the 6r?? you attitude is worse than your assumptions.

    now that ive had my rant, thank you robslave please note that ive actually edited my post because i called you more than a nob head in lines ive deleted. i know you are trying to be helpful but dont put me in the categerory of wanker bikers you have. it pisses me off because im not one of those wankers.

    so, roblsave - thanks, ive googled "head stem bearings" and gain knowledge on this componant of the bike and its relevance to my issue. ive also jacked the wheel and nothing to indicate a worn head stem bearing, or any iregular signs. note i cannot check tyre pressure atm without the tool, but will invest in one. im sure you would approve. im not being sarcastic when i say thanks.


    /\/\ uh... whats this all about. does my bike have this function, is it easy to adjust, do i need tools, why is the standard setting not right from the manufacturer?

  17. He's talking about suspension, lah - specifically if you've been altering it.

    By default jap race bikes are usually set up for short jap riders, go figure. Even still, shouldn't be causing any huge dramas unless you were at an extreme range of height/weight. And the chances of getting the suspension set up perfectly for your height/weight from stock is very low. Yes, its a 6r so it has fully adjustable suspension. If you want to have your bike set up optimally to go fast, or just to have proper suspension set up, you can get it dialed in to you.
  18. Papermate, thank you for that colourful post. :grin:

    My my my, we have a very thin skin don't we. :LOL: I could play the offended poster too if I chose too paperweight, but that would be childish! :p

    Frankly, HTFU mate. You could have gotten a trolling baiting post from some of the trolls around here, but instead you got a word to the wise which told you should flipping well be better acquainted with the basics of your bike. Sorry you took it the wrong way (By the way, there's a very good chance, some of these trollers now have you marked since your skin is so thin! Stay on gaurd mate.)

    Now correct me if I am wrong, but did I actually say anything unfactual?? Did I actually state or imply an opinion about the type of poser you were?? No, don't think I did, but you felt obliged to give me the benefit of your opinion. :roll: FWIW's I'm a kwaka man and approve of your bike choice.

    BUT let's do set the record straight. You my friend, owned yourself by:
    * showing that you don't even know what your basic tyre pressures are - which is basic info in your manual,
    * nor what the basic maintenance routine should be - which is basic info in your manual...
    * and the question of damping and what it is also answered in your owner manual as well - look in the chapter on "suspension"...

    So you still came on line giving lip WITHOUT having read the manual properly. :LOL:

    Ok, so the manual doesn't answer why the settings aren't ideal out of the box, but most of the other q's are.

    Look, you're probably an alright bloke, cool, this is just the internet mate and this is just a lovers tiff, so relax, don't take it to heart.

    Ok, leaving that and the personal dispersions to one side, it's actually been a useful conversation, because useful resources like Trevor or VTRBob or Phizog will know just how much effort to put into their posts and what level to pitch.

    On the point of tyre pressure, tyre pressure is measured by a tyre pressure gauge. It pays to get a good one because bike tyres are very fussy about pressure. In lieu of having a tyre pressure gauge, check your tyre pressure with cold tyres at a shell servo or similar where the pressure measuring part of the gauge is safely away from being dropped or driven over.

    So take a chill pill mate, let's have a chat over a beer... THEN you might be qualified to make those judgements :LOL: :beer:

    :? So I guess an apology for your attitude is out of the question eh?
  19. all good brother, i like you. apology is not out of the question at all. im stubborn at the best of times. i did actually laughed about how people who find this conversation entertaining. forums can be a bit boring. anyway, now that we have poked each others eyes and and decided to suck each other's corks to make up lets move one. cheers, beer time it is.

    ps - jesus christ, people bother being trolls still?

    pps i am jokin about other forums. will check pressures tommorrow and update. ta.
  20. Rob you are a big suck.