Front End Wag?

Discussion in 'Thumpers' started by meat popsicle, May 24, 2005.

  1. meat popsicle

    meat popsicle Ignostic

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    My 03 KTM 640a seems to have developed the tendancy to become unstable at highway speeds recently. There are a couple of things that may contribute to this:

    1) The front end was a bit out of sorts - the fork tubes were not even. I straightened this out (with the torque wrench to boot :ricky) and this seems to have helped.

    2) The front tire is a MT17 DOT knobby. The tire pressure seems to alter its handling drastically (steep profile = bike DROPPED into turns!), so much so that at first 30psi almost made me remove the tire :eek1 But I found ~25psi to be fine and actually like the tire. Recently I may have snuck 30psi back into it (hurrying, sloppy...). But I don't think that is a major factor in the wag.

    3) Front tire install was 10 bucks! :freaky But the buggas were purdy sloppy (had to take the rear back to have it turned around :bluduh) and the front weight is one big fat weight that they screwed up so it just flops up and down on the spoke while walking the bike (slow speed).

    So my questions are this: can a crappy tire balance contribute to front end wag? What's the deal with static vs. dynamic tire balance? Any other ideas appreciated because its an uncomfortable feeling to have the front end start to ossicilate at speed :uhoh
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  2. Loadedagain

    Loadedagain making chips

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    is your wheel true? are yer spokes torqued?

    only time my wheel has ever shaken a spoke was about to break.
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  3. ChrisC

    ChrisC Amal sex?

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    Come on Loaded....wag your front end a little.... :evil
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  4. Loadedagain

    Loadedagain making chips

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    one more... tcoh had major head shake on his 950 and it tossed him off the bike on the freeway. i believe his problem was due to a loose headshaft. is yours tight?
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  5. txrider

    txrider Been here awhile

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    Yes.

    Mine inproved a lot after balancing, but it was unbalanced with a rimlock so I doubt yours is as far off.
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  6. AusieRob

    AusieRob Just Gas It!!

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    Unstable? a bit of an open a discription, my wife calls me unstable but I don't think I have a front end problem, maybe.. :dunno
    By oscillation you mean - Moving up and down or left and right?

    Yep, that'll do it.

    Yeah, tire preasure is a contributor.

    Not great, I'd crimp that sucker on so it don't move. Anyway, if this was wrong you'd get more a vibration (front moving up and down) that typically gets worst and better at different speeds. Is that what you mean by oscillation? Moving up and down or left and right?


    Like Loaded said, check the headshaft. That can lead to very bad stuff at speed..
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  7. meat popsicle

    meat popsicle Ignostic

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    thank you for the replies. i will check the spokes - not sure how to check the wheel true 'cept for spinning it and takin a gander. loose headshaft... um, whazzit? :scratch can't be the axle; must be the steering head, between the two forks right? :ear I just retorqued it when realigning the front end; will recheck. thrown off! :eek1

    so aboot this "Dynamic" vs. "Static" wheel balancing... :ear :ear

    I hear dynamic means "two plane" wheel balance. nice linkey:

    http://www.toyo.com.au/tech_info6.html

    :D
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  8. meat popsicle

    meat popsicle Ignostic

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    oscillate, or wag, meaning left-right, like when you turn the handlebars left right. it just starts as a light oscillation that grew in amplitude until I would say "woah!" and back off. now I back off and have started avoiding situations that seemed to spawn it (like hitting some groves or bumps at speed while lane changing).
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  9. Hipster

    Hipster Long timer

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    I had the same problem, it was caused by the front tire bead not being properly seated. Make sure the tire bead is centered on rim on both sides of the tire.
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  10. meat popsicle

    meat popsicle Ignostic

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    holy hand grenades batman! that would be a bad install job. might have to go back for "reducation" purposes... :mrskbasa

    although I have done about 1000 miles since the install so I guess its purdy stable.
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  11. AusieRob

    AusieRob Just Gas It!!

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    Would the term "headshake" work? ie is it a high or low frequency oscillation?

    Have you tried lifting the front end (centerstand, have your SO siting on the back :D )
    - Spin the front wheel to see if spins true. A pointer held against a fork can give a good guide. Check the tire is true as well.
    - holding the bottom of the forks (at the axle) Try to move the wheel/forks forward and back.
    - also check for left and right movement.

    -also check the wheel bearings are good. Hold top and bottom of the wheel and try to move it.
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  12. Loadedagain

    Loadedagain making chips

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    good point rob....

    how are yer wheel bearings meat? how are your head bearings also? how often have you re-packed them? manual says once a year. done that?
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  13. Stephen

    Stephen Long timer Supporter

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    Check:
    swingarm pivot
    rear axle and bearings
    rear wheel
    rear spring and damper

    Is that new rear tire real wide? Does it plant a real wide foot print? Does it have tall soft sidewalls?

    Everything is connected to everything else. The Buddha said it, Lao Tsu said it, my chiropractor said it, and some dirt racing guy I ran into once said it.
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  14. meat popsicle

    meat popsicle Ignostic

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    headshake sounds good; its like a wobble. well its more towards low frequency oscillation - definately not in the direction of a vibration.

    great suggestions Rob, I will look into it.

    I just QA/QCed the front and torqued the head nut to spec but I can check it again. Part of that process was lifting the front end and pulling on it to check its play. Seemed ok (is it pretty obvious when its loose? :ear).
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  15. meat popsicle

    meat popsicle Ignostic

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    'taint been a year - well right abouts now! Guess that's on the list now! thanks for the heads up! :thumb
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  16. meat popsicle

    meat popsicle Ignostic

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    check the rear end? grasshopper thanks you :bow

    the Michelin Desert rear seems pretty stiff to me (HD fer shure). it is a 140/90-18 as compared to the Metzeler Sahara III 140/80-18 stocker. Um, the book would say its just a bit taller, but we all know the tire mfgs. make this stuff up so it might be wider. I have a new set of Metzeler Saharas sitting in the garage; I can compare. Come to think of it, the Desert is probably somewhat softer and taller than the Sahara :nod Why? :ear
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  17. Stephen

    Stephen Long timer Supporter

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    Think about it.


    C'mon, you can do this.


    If the rear were to put drive to the ground unevenly (by whatever cause), what would happen? If the rear moves from side to side -- somehow -- where would you feel it?

    You mentioned that a bump often sets your low frequency oscillation -- which sounds like a weave and certainly not headshake (which btw, is started by grab-slip-grab of the rear wheel under power). This implies that something in your suspension is not settling as quickly as it should. If your rear spring rate and damping are good, and all the joints and bearings are free of play, that kinda leaves the tire as the remaining piece of the suspension.

    There are a lot of variables in this phenomenon we call "steering". If you ride enough crappy bikes you eventually begin to get a feel for what's doing what. I can usually ride a bike and start to get an idea, but I'm pretty inarticulate about how I get to a conclusion. Still, this all started when you switched tires, right? That's a clue.

    Another clue -- one that takes us away from the "feel the front, fix the back" chestnut -- is that lowering your front tire pressure seemed to improve things. I have only anecdotes about this: When I put more roadish tires on the old KLR, I put a roadly 32psi in the front instead of the factory spec 21 and got twitchiness and even a few little speed wobbles for my trouble. Back to 21 and it's all good. When I put TKC's on, again I upped the pressure, and got twitchies -- no wobble, but damned uncertain-feeling. Back to spec, okay, so I'm a slow learner. I wouldn't imagine that your off-road tires were intended to carry 32 psi.

    Good luck, have fun.
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  18. meat popsicle

    meat popsicle Ignostic

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    :scratch

    I think you overestimate me...

    well these are knobbies, that can flex. plus i do run them down to 20psi when getting offroad; that would let the sidewalls flex more. i have felt the rear wobble in my seat and recognized it as the rear tire. but that was at slow speeds. at highway speeds - and i am talking 70-80mph here - i believe you are implying that rear wobble gets translated thru the bike and can manifests itself as "headshake". interesting...

    a description of the phenomenons would certainly help clarify and get everyone on the same page. i will have to look around but fear i will not find a dictionary of moto terms. anyone care to elucidate? :ear

    Just a thought: the fact that the oscillation occurs could be from many things, but what would make it continue - that is the key I am looking for; the imbalance to steal from Stephen.

    my phenomenon feels like the bars want to turn right-left-right-left each second, and don't stop until i come off the gas or restrain the bars. certainly not a "vibration" in my sense of the word, more like a shake... but maybe "weave" is more correct? :dunno

    rear suspension is pretty stock, but the WP is a good setup; it is factory setup for 165 and I am 200 so it's undersprung a tad. suppose i could tweak it a bit but really it needs a few hundred bucks to be stellar; same with the forks. the joints and bearings should be fine; it has less than a year of not terribly rough riding on it :cry such is my fate.

    additional info: i had the tires put on prior to a 700 mile trip where i tore across the state at 80mph rode dirt for a couple of days and then tore back. during that whole time I didn't notice this phenomenon and felt pretty secure with the bike at speed on the highway. now it's changed.

    Coulda been partially due to the front being unaligned; what about rear wheel alignnment? I just did chain maintenance... I measure the distance on both sides from the swingarm pivot to the rear axle to align the rear; seems to work well. Could also be tire pressure as you have also found. I was also thinking maybe its tire wear; especially if its uneven tire wear due to a shoddy balance job. that is where my dynamic vs. static tire balancing question came in. anyone? :ear

    i never put more in the tire than the carcass specs as the max. they can hold 30psi - some more likely (tire ain't in front of me) but i don't top em off anymore. i will drop them back down to 25 and see if that helps first. report to ensue in the near future - i will also perform the check suggested by all y'all, iteratively, to see if this can be pinpointed.

    damn y'all are helpful! :D
    #18
  19. potatoho

    potatoho Cheese and Rice!

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    My dealer did that too. Big hunks of lead. Crimping didn't improve, so I auto gooped them to the spoke. I did find some sectioned weight strips at the NAPA store but haven't replaced them yet. I was afraid they'd mount my rear tire backwards, or rather forwards, so I put big arrows on each rotor before I brought them in.

    As for steering oscillation, I was having some recently even with my stabilizer. It was the tiny bit of play between the lever and post, and it went away once I fixed that up. It would oscillate within that small range to where it bugged me, and without the stabilizer attached it was fine. So I would probably check to make sure you don't have any weird binding in the steering. I remember one time I had a cable or some plastic rubbing and that caused enough resistance to mess with my steering.
    #19
  20. Buckster

    Buckster Banned

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    My '04 shakes its head a little at 80mph with the TKC80 fitted, if I run 26 psi it is hardly noticeable, either way it is just a small wag.
    #20