high speed shakes- Mtbr.com
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  1. #1
    blet drive
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    high speed shakes

    Has any one gotten the high speed shakes on there way home from work. I did the other night and it was very scarey. shook so hard that my lights went out . i got one foot to the ground. I think that saved me from crashing. wore right threw the carbon sole..
    Attached Thumbnails Attached Thumbnails high speed shakes-curts-shoe.jpg  

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  2. #2
    poser Administrator
    Reputation: rockcrusher's Avatar
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    I got a high speed wobble at 42mph on a mountain descent on my Ti road bike. I think I tracked it down to the Ti frame, a flimsy fork, too light of wheels and a fat ass rider. I now stay below 40mph.

    While researching the effect i found that it is mostly from a resonance in the frame, being over loaded, or having a wheel out of true can enhance the effect as can gripping the bar too hard. Solutions are to not brake as that will add to the effect but to put your knee on the top tube to try to shorten the phase of the resonance. Neither of which i have attempted because i am in no hurry to reproduce the effect ever again.

    Glad you didn't crash scary as hell though isn't it?
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  3. #3
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    I have had the same on an light weight aluminium frame road bike at around 60~65Kmph, and it is pretty terrifying. In my case it was the front wheel setting off the vibrations - this may not sound believable but I had the magnet for the speedo on a spoke next to the valve moving it opposite the valve dramatically reduced the effect. It started occurring again when the wheel went out of true

  4. #4
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    Been to 95 kph never has a speed wobble, but then I am riding an old Rocky Element rather stiff and straight.....with high end wheels.

  5. #5
    CB of the East
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    I'm not sure what I'm looking at in that shoe picture but it don't look good.

    I've never had them that bad on any of my current bikes. I think I might have had some mile ones on a previous bike but never got over critical mass speed. I top out at about 45mph most of the time.

  6. #6
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    The one time I had it kick it responded to moving my hands and letting up on the grip. This is very counter intuitive/instinctive preservation (ancestral genes for clinging to shaking tree branches?). Anyway it shut down immediately. Good as it was just in time for a corner and avoiding a tree right at the edge of the pavement. Not today, boy-oak! A friend had a Peugeot (steel, lugged frame) decades ago do it too, and it backed off with the legs against the top tube but he got rid of it for that 'feature'.

    BrianMc
    Last edited by BrianMc; 08-15-2012 at 06:39 PM.

  7. #7
    blet drive
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    Civia Cycles

    this is the bike that i got it on.
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  8. #8
    blet drive
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    bedwards: that is the heel of my shoe after i put it down to try and stable my self out
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  9. #9
    weirdo
    Reputation: rodar y rodar's Avatar
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    Quote Originally Posted by JUNGLEKID5 View Post
    bedwards: that is the heel of my shoe after i put it down to try and stable my self out
    I know you already said it was your shoe, but it sure looks like kneeburger!

    Man, that does sound scary. I`ve been to between 50 MPH and slightly above on a handful of ocasions with at least two bikes and never had that pleasure- hope I never do. How fast were you going when it happened to you, Junglekid?

  10. #10
    Bedwards Of The West
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    I have gotten that on my Access 29er frame with Big Apples. It started when I was on a downhill and sat up (let go of the bars) to zip up my jacket... I think those tires are so heavy it doesn't take much of an imprefection to set things in motion. I was able to stop it by just grabbing the bars, but it really went crazy for a minute. I was able to reproduce it by letting go of the bars while leaning forward, and then slowly sitting up to shift my weight back. When my weight got back behind a certain point...shakes. I have basically the same set up on my Ogre, and haven't been able to get it to do it. Steel is real, I guess?
    You have no excuse for driving to work
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  11. #11
    DIY all the way
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    Back in the day (like 20 years ago), I had the same issue. I did some testing of air flow and a bit of research, to have an explanation.

    First I did some air flow testing. It turned out that the most messy turbulent place, is in between the fork blades, where the spokes are moving at double ground speed velocity.

    I did a bit of head scratching, and figured the reason for the wobble, had to be the spokes pushing and pulling sideways, when inside mentioned mess.
    I had the issue at around 80km/h and up, but nothing below that.
    I concluded it was a matter of slowing down the air velocity between the fork blades.
    This I sorted by making a carbon fork, with fork blades profiled like a glider wing, with the flat side facing inwards.
    This would in theory reduce the air flow, thus the velocity as well, between the fork blades, by approx. 20%.

    I took the bike up to 95km/h with that fork, and didn't get even a hint of wobbling.

    My conclusions may be flawed, as I didn't have a valid null test, but I think I'm not too far off the mark.

    Still have that fork somewhere


    Magura

  12. #12
    blet drive
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    Quote Originally Posted by rodar y rodar View Post
    I know you already said it was your shoe, but it sure looks like kneeburger!

    Man, that does sound scary. I`ve been to between 50 MPH and slightly above on a handful of ocasions with at least two bikes and never had that pleasure- hope I never do. How fast were you going when it happened to you, Junglekid?
    I dont know how fast it was.. but none the less scarry...
    Save a tree & wipe your butt with an owl.
    Thank your local Sierra Club.

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