stefmeister Posted September 8, 2020 Posted September 8, 2020 Typically it is a matter of harmonics. Dampening it by clamping the toptube with your knees solves the problem. Yup, boils down to the resonant frequency of the system (harmonics).Similar thing happens when you're carrying a cup of coffee, after 9 (iirc) steps, the resonance causes you to spill your coffee no matter how hard you try to balance the cup whilst walking. DieselnDust 1
TNT1 Posted September 8, 2020 Posted September 8, 2020 Around 50km/h plusAccelerate. Go faster until the wobble goes away. Shaunpr 1
LongDonkey Posted September 8, 2020 Posted September 8, 2020 Accelerate. Go faster until the wobble goes away.Some of this advice is a bit like when they invented cars/motorbikes that could go faster than a horse. The theory was you would die in a fiery ball of death and carnage if you ever went faster than a horse could run. The horse barrier. Shaunpr 1
Edereese Posted September 8, 2020 Posted September 8, 2020 Clamp the top tube and don't look at the wheel, even if it does wobble, looking at it will only make your reaction worse. That is if everything else is in order, wheels trued, tight, headset sorted etc..
TNT1 Posted September 8, 2020 Posted September 8, 2020 Some of this advice is a bit like when they invented cars/motorbikes that could go faster than a horse. The theory was you would die in a fiery ball of death and carnage if you ever went faster than a horse could run. The horse barrier. When you're sliding along the tar at 50+, you at least wont be wobbling... Hairy and Pure Savage 2
Hairy Posted September 8, 2020 Posted September 8, 2020 a Hopf Bifurcation isn't as severe as mechanical resonance i.e. the structure usually won't shake itself apart. It's a point of rising instability which then abates once you go over it. Sort of like the sound barrier for a layman example.So what you are saying the OP should just ride FASTER and hit something like 75km/h to go past the point to where it abates DieselnDust 1
Hairy Posted September 8, 2020 Posted September 8, 2020 Yup, boils down to the resonant frequency of the system (harmonics).Similar thing happens when you're carrying a cup of coffee, after 9 (iirc) steps, the resonance causes you to spill your coffee no matter how hard you try to balance the cup whilst walking.That usually happens to me after the 1st step stefmeister 1
Hairy Posted September 8, 2020 Posted September 8, 2020 When you're sliding along the tar at 50+, you at least wont be wobbling...you will be wobbling when you get up though .... it is knows as the delayed wobble effect TNT1 1
Hairy Posted September 8, 2020 Posted September 8, 2020 So after a couple of off the cuff poor attempts at humour. I used to have a steel roadie that would get a wobble at high speeds, gripping the top tube with the knees certainly did the trick for that bike. Shaunpr and Grey Hubs 2
eddy Posted September 8, 2020 Posted September 8, 2020 (edited) So what you are saying the OP should just ride FASTER and hit something like 75km/h to go past the point to where it abates Yip. If the speed changes sufficiently, the conditions that caused the wobble go away and you have control again. Not sure I'd be brave enough to try it, but apparently it works. Maybe if your goolies are big enough to try it, you can just hang them down either side of the top tube and let their weight dampen the frequency. Edited September 8, 2020 by eddy Hairy 1
Gerhard765 Posted September 8, 2020 Posted September 8, 2020 Decent article on it hereInteresting read, thanks for sharing. I don't see that they go into vortex shedding. I could not help but wonder if that is also a cause of induced vibration. Not that I am saying that this is the cause of the OP's "Shimmying" but this is becoming an interesting technical thread to follow.There is some CFD's shown in the Zipp 454 wheel video showing what the vortex shedding can do on wheels.https://youtu.be/9I3pnXWpDvI look at timeLook at time 3:40. The vortices will act as sideway forces on your rim. For an example of vortex shedding:https://www.youtube.com/watch?v=8OExYy28moc
DieselnDust Posted September 8, 2020 Posted September 8, 2020 vortex shedding..... ROTFLMAO A bicycle doesn't go fast enough to generate a vortex of enough intensity to shake a 80kg ride and bike combo... unless you strap a RATO pack to the seat stays TNT1 1
TNT1 Posted September 8, 2020 Posted September 8, 2020 Interesting read, thanks for sharing. I don't see that they go into vortex shedding. I could not help but wonder if that is also a cause of induced vibration. Not that I am saying that this is the cause of the OP's "Shimmying" but this is becoming an interesting technical thread to follow.There is some CFD's shown in the Zipp 454 wheel video showing what the vortex shedding can do on wheels.https://youtu.be/9I3pnXWpDvI look at timeLook at time 3:40. The vortices will act as sideway forces on your rim. For an example of vortex shedding:https://www.youtube.com/watch?v=8OExYy28mocExcellent marketing gimmick from zipp.
Gerhard765 Posted September 8, 2020 Posted September 8, 2020 vortex shedding..... ROTFLMAO A bicycle doesn't go fast enough to generate a vortex of enough intensity to shake a 80kg ride and bike combo... unless you strap a RATO pack to the seat staysRead my comment. I did not say that this is the cause. As engineer I am curious of what can cause things which should not happen. DieselnDust 1
Shaunpr Posted September 8, 2020 Author Posted September 8, 2020 Are those with the Mavic wheels? I would suggest sitting on the top tube, but its a canyon. Yes Mavic
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now