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Bike has a case of the deathwobbles

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Unconnected, May 6, 2012.

  1. Hey all, so my new VFR has been going very well since i got it from ad91on.

    However recently it has developed a case of the death wobbles if i take my hands off the bars at anything above 70ish, the shaking becomes quite violent after about 5 seconds or so.

    Im really not sure what could be causing this, the bike used to be super stable with no hands at 70+, as in, so stable i remember remarking to myself just how long i could ride it with no hands compared to my old hornet.

    In the last few days the following has happend which i think might be causing the issue, and would like some advice:

    1. i recently changed tire pressure, am now running 30 front and 32 rear down from 40 front and 40 rear, which is what ad91on was running, honda adivce 32/34 FYI.

    2. i recently dropped it (again) after i locked up the front (prior to dropping pressures, which may have been a contributing factor to locking up). This shifted my RHS clipon, i have since loosened and remounted the clip on and lined it up with the LHS ones angle as best i can.



    3. perhaps bike lost a wheel weight when i dropped it?


    anyway the bike rides fine, so long as i have my hands on the bars that is.

    any tips?
     
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  2. Wack the tyre pressure back up and try again. Simple trial and error.
     
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  3. Eeeek.

    42 rear, 36 front is what is recommended. At least according to a web search. Sounds much much more reasonable than 32/30.

    Don't ride it again till you check for sure. What does the tyre say?
     
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  4. If it's had a fall there's a chance the fork legs are twisted in the yokes, which could put the front wheel out of alignment enough to set up the instability. It will pay to check it.
     
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  5. That sounds like wheel bearing to me or slight chance maybe head stem bearing.....check it out.
     
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  6. 36/42 is usually the recommended tyre pressure for bikes with a 180 on the back. I'd double check with Honda - maybe the first guy you spoke to was the intern?
     
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  7. just to make sure everyone saw my sig and realised that i have a 24 year old VFR400R not a VFR800fi or anything reliable.

    i think fork twisting could be the cause, ill get it checked out.

    as for pressures, my tires are extremely skinny and i have quite a lot of power and very bad bais ply tires (no radials fit).
    my sizes are:
    130/70/18
    100/90/16

    this bike thus has very tiny contact patches, i felt with 40/40 the bike would have even less as the tire would not deform as much and spread out under load. hence why i dropped them after i locked up twice and dropped it due to that lock up once, i figured the brakes stopping power massively outweighed the tires stopping ability.

    after i dropped the pressures the bike has been much much better, however i have noticed it is very tiring to ride the bike, counter steering and such at high speeds must be done with much more force after a 5 hour ride i was ****ed.

    i will increase them to 32/34 this is apparently what honda said. The reason the tires are so low is because i wanted to prove my theory, so i went to the lowest psi i though was acceptable. This was to ensure i noticed the changes.
     
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  8. 30/32 is good for track, but definitely not good for road. I'd try and bump the tyre pressure up a bit more. Try 34/36 and then 36/38 and see how you go. 40/40 is a bit excessive I think though.
     
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  9. If your rear rim is 3.5 you could run a BT92 Radial,they come in a 140 rear.I loved them but the 55 aspect made for a gearing problem so I dont use them anymore.I had a BT023 front and they gave very impressive grip.BTW I would go higher tyre presures and start of the front and work my way completely through the bike looking for play.Wheel bearings,steering head bearings,swingarm and rear suspendion bearings ect ect.Wheel alinment as well.
     
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  10. I found the same with my XJR1300, when i changed the front tyre it dissapeared completely. I was told that a front tyre that has a flat spot from too much highway riding develops the issue.

    Not sure whether it was BS or not, but seemed logical at the time... How worn is the front tyre?
     
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  11. definitely tyre pressures, in particular the rear. Also check for scalloping in the front.
     
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  12. if the tyre's worn abnormally you get the tyre scalloped and it handles very weirdly. run your hand over the tyre and see if it feels bumpy
     
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  13. Everybody above is right. The order I would be addressing it would be:
    -Tyre Pressure (smaller tyres need larger pressure, so low 30s for these is definitely not correct)
    - Tyre wear (just because it's easy to do)
    - Triple clamp misalignment (things can shift in minor accidents without bending forks)
    - Steering head bearings
    - Wheel bearings (though you can usually hear these when they are shot)
    - Bent forks.
     
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  14. ok so upped the tires pressures to 32/34, which is what im told Honda reccomends. It did not however stop the shaking, though i do think its improved the handling. Will step it up to 34/36 and 36/38 and see whats best over the next few days. Also on a side note, whats the deal with tire pressures and the two times tables?

    Tires are wearing fine no scalloping or anything of the sorts.

    I will be taking the bike into the mechanics soon to have the front suspension measured so i can get some new fork springs/spacers etc made for the bike. I will get the mechs to also see whats causing the issue re the deathwobbles.

    Hopefully i have not bent the forks just twisted them, it was not even a crash just a lock and drop at 10kph, somehow i think its going to be hard to find new forks for a 24 year old grey import bike that shares no suspension components with any other honda.
     
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  15. Hey buddy,

    When i put those clip ons on the bike which are substantially lighter than the stock bars, i noticed slightly more shaking than stock. You may want to put some bar end weights into the counteract it a bit, i know other bikes have them.

    Whenever I ran lower pressures death wobbles were much more readily available. That's why I always had that rock hard 40/40 as i found it best for the road. On track I dropped it to 30/30 which was a lot grippier but only at those higher temps.

    I doubt the forks are the problem. I would have replaced the bearings if they needed them. I would put the pressures back up and maybe put some bar end weights on and if it is still happening THEN freak out.

    Hope the bike is treating you well otherwise! I miss that things ridiculous noise!
     
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  16. Nothing, I think it's just a round number and people don't like primary/odd numbers. I mean if 32/34 is meh, and 34/36 is also meh...then go with 33/35...or 33/33, or 33/34...it's up to what's comfortable for you.
     
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  17. Yep ad91on, it was the tire pressures for sure. currently running 34/36 and there is significantly less deathwobbles / its fine again. Ill pick up some bar ends and see if that kills the vibrations even more so, though even coming from an I4 i cant say that the V4 is significantly worse for vibrations.

    Anyway thanks for your help guys.

    Hope your enjoying the hornet as well ad91on.
     
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