Advertise on Bikeforums.net



User Tag List

Results 1 to 18 of 18
  1. #1
    Gios my baby hiromian's Avatar
    Join Date
    Dec 2005
    My Bikes
    Gios 96, Mercier 72, Peugeot 74 X 2, Sears full suspension High rise banana seat, Kona 94, CCM Rambler 70s.
    Posts
    1,135
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    high speed wobble

    I experienced this for the first time last week decending a mountan at 70K/h. Ahh that was scary. I got out of trouble by not panicing, siting up a bit, bleading off speed with the rear brake which did not do anything to stop the wobble so I pressed my knees into the top tube. Bingo, presto, wobble gone. I have done these high speed decents plenty and since and it has only happened the once.

    What is the cause?
    "Aiyah...Oh no"

  2. #2
    Slow'n'Aero DrWJODonnell's Avatar
    Join Date
    Feb 2006
    Location
    Driving the pace in the crosswind
    Posts
    2,599
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    sometimes a harmonic feedback frequency can be set up in your fork, frame, or handlebars. Other times it can be equipment failure (out of true wheel, broken skewer, cracked frame or fork). Finally it can be due to extreme changes in gravitational center. If you were in a normal position, that is not it. I would inspect everything VERY carefully.

  3. #3
    Senior Member
    Join Date
    Jul 2006
    Posts
    1,085
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Putting more weight on the front wheel cures this for me, ive had it happen quite a bit decending at 45k/hr with my hands off the bars.
    Cat 1 o-meter 33%

  4. #4
    . botto's Avatar
    Join Date
    Jan 2006
    Posts
    40,335
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    also throw in the possibility of a loose headset into the mix.

  5. #5
    Isaias NoRacer's Avatar
    Join Date
    Sep 2005
    Location
    Essex, MD
    My Bikes
    Ridley X-Fire (carbon, white)
    Posts
    5,174
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by DrWJODonnell View Post
    sometimes a harmonic feedback frequency can be set up in your fork, frame, or handlebars.
    I used to have this occur when I first got my Giant. It stopped when I changed my seat height.
    2009 mileage = 14,738 miles; 2010 mileage = 15,234 miles; 2011 mileage = 17,344 miles; 2012 mileage = 11,414 miles; 2013 = 12,169

  6. #6
    Making a kilometer blurry waterrockets's Avatar
    Join Date
    May 2006
    Location
    Austin (near TX)
    My Bikes
    rkwaki's porn collection
    Posts
    26,028
    Mentioned
    19 Post(s)
    Tagged
    0 Thread(s)
    Yeah, I'd check everything over really carefully. I've never had this happen with my hands on the bars at speeds as high as 60mph.

    I'll add to the mix to check that your front spoke tension is still high enough, in addition to DRW's trueness check.

    My current bike will occasionally shimmy over 30mph with hands off the bars, but what can you expect from a 62cm frame?

  7. #7
    . botto's Avatar
    Join Date
    Jan 2006
    Posts
    40,335
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by waterrockets View Post
    Yeah, I'd check everything over really carefully. I've never had this happen with my hands on the bars at speeds as high as 60mph.

    I'll add to the mix to check that your front spoke tension is still high enough, in addition to DRW's trueness check.

    My current bike will occasionally shimmy over 30mph with hands off the bars,
    but what can you expect from a 62cm frame?
    a jungle gym on wheels?

  8. #8
    Tiocfáidh ár Lá jfmckenna's Avatar
    Join Date
    Dec 2003
    Location
    The edge of b#
    My Bikes
    A whole bunch-a bikes.
    Posts
    5,401
    Mentioned
    0 Post(s)
    Tagged
    1 Thread(s)
    Quote Originally Posted by hiromian View Post
    I experienced this for the first time last week decending a mountan at 70K/h. Ahh that was scary. I got out of trouble by not panicing, siting up a bit, bleading off speed with the rear brake which did not do anything to stop the wobble so I pressed my knees into the top tube. Bingo, presto, wobble gone. I have done these high speed decents plenty and since and it has only happened the once.

    What is the cause?
    3 of my bikes have high speed wobble. They are all big frames and I believe that has something to do with it. Two are lugged steel and the other is AL. My TI compact frame rides straight and true at any speed. Knee on TT is all I need to do so when ever I descend I clench the TT (or just one knee touching) which is a good aero position anyway.

  9. #9
    Making a kilometer blurry waterrockets's Avatar
    Join Date
    May 2006
    Location
    Austin (near TX)
    My Bikes
    rkwaki's porn collection
    Posts
    26,028
    Mentioned
    19 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by botto View Post
    a jungle gym on wheels?
    That makes the price justification that much easier

  10. #10
    Texas Fight! UT_Dude's Avatar
    Join Date
    Oct 2006
    Location
    Austin, TX
    Posts
    2,023
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by waterrockets View Post
    My current bike will occasionally shimmy over 30mph with hands off the bars, but what can you expect from a 62cm frame?
    For it's owner to not be so frigging tall, duh.
    T E X A S F I G H T !
    http://www.chriscollins.org

  11. #11
    Banned
    Join Date
    Jun 2006
    Location
    United States
    My Bikes
    roadbikes and full-suspension mountainbikes
    Posts
    1,929
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Tire pressure correct front and rear? Headset? Too many peripherals/electronics attached to handlebars?

  12. #12
    Isaias NoRacer's Avatar
    Join Date
    Sep 2005
    Location
    Essex, MD
    My Bikes
    Ridley X-Fire (carbon, white)
    Posts
    5,174
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Sheldon Brown has this article from Jobst Brandt regarding Shimmy or Speed Wobble:

    http://www.sheldonbrown.com/brandt/shimmy.html
    2009 mileage = 14,738 miles; 2010 mileage = 15,234 miles; 2011 mileage = 17,344 miles; 2012 mileage = 11,414 miles; 2013 = 12,169

  13. #13
    Gios my baby hiromian's Avatar
    Join Date
    Dec 2005
    My Bikes
    Gios 96, Mercier 72, Peugeot 74 X 2, Sears full suspension High rise banana seat, Kona 94, CCM Rambler 70s.
    Posts
    1,135
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by NoRacer View Post
    Sheldon Brown has this article from Jobst Brandt regarding Shimmy or Speed Wobble:

    http://www.sheldonbrown.com/brandt/shimmy.html
    Thanks for the link. Thanks all for the responces.

    I did a thorough check on the bike and found the rear wheel to be a little more out of tru than I like. The wobble initiated in a corner and I think the freqency of the rear tire wobble (more pronounced in a corner yet undetectable by me), + feedback with the frame built up the resonance. My knee pressing the frame broke the cycle.
    "Aiyah...Oh no"

  14. #14
    Slow'n'Aero DrWJODonnell's Avatar
    Join Date
    Feb 2006
    Location
    Driving the pace in the crosswind
    Posts
    2,599
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Another satisfied customer.

  15. #15
    Senior Member DannoXYZ's Avatar
    Join Date
    Jul 2005
    Location
    Saratoga, CA
    Posts
    11,495
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Glad you found the problem. Yeah, I've found that slightly out-of-true wheels, either at the front or rear and start a sympathetic vibration in the frame. Clamping your knees on the frame will dampen the vibrations.

    A long-term fix is truing the wheels and stiffening up some part of the frame/fork will raise the oscillation-frequency to higher speeds than you'd ever be able to accomplish. On my bike, going from an alloy fork to a stiffer carbon one moved the speed where the wobble can barely be felt from 55mph to 72mph (which I'd hit maybe once a year if I can find just the right mini-van coming down San Marcos Pass ).

  16. #16
    Race to train jrennie's Avatar
    Join Date
    May 2005
    Location
    suffering on the back
    Posts
    3,115
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by recneps View Post
    Putting more weight on the front wheel cures this for me, ive had it happen quite a bit decending at 45k/hr with my hands off the bars.
    Why do you decend with your hands off the bars

    if you see recneps on a downhill

  17. #17
    Junior Member gr8rcake's Avatar
    Join Date
    Feb 2008
    Posts
    10
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    It could also be caused by a wheel that appears true but is supported by a loose hub which aggravates the problem.

  18. #18
    Village Idiot
    Join Date
    Jan 2007
    Location
    Bahstaaaaan
    Posts
    19,916
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jrennie View Post
    Why do you decend with your hands off the bars

    if you see recneps on a downhill
    I've ridden downhill on short descents no handed, I'd just got my CAAD9 and I was just blown away by how straight it tracked. I don't make a habit out of it, especially now...
    Truth, like light, blinds. Falsehood, on the contrary, is a beautiful twilight that enhances every object.
    -Albert Camus

    Hammer Nutrition 15% discount!!!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •