Canyon Aeroad Disc - Shimmy

Discuss light weight issues concerning road bikes & parts.
DamonRinard
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by DamonRinard

Miller and sungod nailed it.

Every bike has a natural frequency (as does every physical system), and you found yours. Changing anything can change the system, so TonyM found changing spoke tension changed his system.

To repeat sungod's good advice, the main two ways of stopping shimmy are:
(1) clamp the top tube with your knees, or
(2) stand up off the saddle, just a little.
Just pick one, no need to do both.

Both these techniques work by changing the system's stiffness, thus its natural frequency, to one which you are not experiencing at the moment your bike starts shimmying. Gripping the top tube stiffens the system, standing up makes it more flexible. Stiffening raises the natural frequency (you'd need a higher speed to get wobble going); making the system less stiff decreases the frequency (the bike would wobble at a lower speed, but that's okay, you're not at that lower speed at the critical moment).

With either of those two reactions you can immediately stop shimmy on any bike, any time, any where.

To cure the bike, increase the system stiffness. Usually the most flexible parts are the frame & fork, maybe wheels or tires (higher inflation pressure raises the stiffness thus the frequency thus the speed at which shimmy can occur). So if you're thinking of new wheels, give 'em a try, they may change the stiffness in a beneficial way.

In the 1970s I had a high-end Holdsworth racing bike that would shimmy at 17.5 and 35 mph. So you can get multiples of the natural frequency. In those days everyone knew to clamp the knees on the top tube. But with modern bikes that are stiffer, the occurrence of shimmy has decreased and there's now a generation of riders, many of whom have never experienced shimmy, so the knowledge of how to live with it and control it is less commonly known. Narrower frame tubes, whether for styling or in an effort to reduce frontal area or weight, are typically less stiff and so we have modern bikes that are just flexible enough to wobble sometimes if conditions are just right (or just wrong, depending on how you look at it).

More explanation from Jobst (as always) in his FAQ:
https://www.sheldonbrown.com/brandt/shimmy.html

Here's a nice video where I induce shimmy in a road bike:
https://www.youtube.com/watch?v=xODNzyUbIHo
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

by Weenie


dcorn
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by dcorn

Check the headset for play. I have a helluva time keeping the Acros headset feeling tight, which can make the steering a bit wobbly.

Mr.Gib
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by Mr.Gib

Bordcla, judging by some of the questions you are asking, I would encourage you to make sure ever detail of your bike is in perfect condition. The wheels obviously need to be serviced by someone with the appropriate skills. Once properly tensioned, ask them to secure the nipples with wicking loctite (290 iirc).

You are about to undertake some ambitious riding and you cannot do that with doubts in the back of your mind. In addition to the very good information posted already, remember the bike and all its parts are a system. Sometimes simply changing a stem can make a difference, although handlebars are likely to do more. Of course short of changing the frame itself a different set of wheels (heavier/stiffer) are your best bet if you can't get the current set-up working properly.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

Bordcla
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by Bordcla

The handlebars are indeed very loose (they move side-to-side super easily), but do not knock in any direction. As long as it's not knocking, does the steering need to be any tighter? (My understanding has always been: as loose as you can as long as it doesn't knock...)

check6
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by check6

Bordcla wrote:
Tue May 29, 2018 12:27 am
The handlebars are indeed very loose (they move side-to-side super easily), but do not knock in any direction. As long as it's not knocking, does the steering need to be any tighter? (My understanding has always been: as loose as you can as long as it doesn't knock...)

I *just* got my Aeroad 9.0 SLX disc and had to make sure the headset was right after a ride where it just seemed a little too loose for my liking. Here is what I did that was a little out of order for what I do on my other bikes: Lossen the dust cap and the stem bolts. Tighten the "internal" headset tension bolt to 4nm as prescribed. Then tighten dustcap to 2nm, finally evenly tighten the stem bolts to 5nm. Since doing this in the proper order the headset has been tight like a tiger.

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TonyM
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by TonyM

Bordcla wrote:
Tue May 29, 2018 12:27 am
The handlebars are indeed very loose (they move side-to-side super easily), but do not knock in any direction. As long as it's not knocking, does the steering need to be any tighter? (My understanding has always been: as loose as you can as long as it doesn't knock...)
You may have found the problem..... :smartass:

I would recommend you to tighten your headset correctly and also look at the torque recommendation of the manufacturer.


Remember also that headsets have to be checked a few hundred/ thousand kilometers after the first setup (or after the bike purchase if your purchase it already assembled etc...) as they are usually slightly loose.

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Miller
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by Miller

People, it's not about the precise spoke tension or headset adjustment. Damon's post above explains what's happening with shimmy. The basic takeaway is that if you grip the top tube with your legs as you go into a descent, shimmy will not happen.

jeanjacques
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by jeanjacques

Miller wrote:
Tue May 29, 2018 7:24 am
People, it's not about the precise spoke tension or headset adjustment.
But as Damon explained, if I understand right, tighten the headset "increase the system stiffness" and change the shimmy fequency.
Now it will occur at 30km/h for a more regular training :lol:

bm0p700f
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by bm0p700f

It is resonance. If you go faster it goes away. It is caused by particular wheel fork combinations combined with head tube angle.. air flow around the wheel and fork seem to set it off and once the ocillation starts it is self reinforcing.

Change the wheel and the residence point should shift and hopefully go away. In fact changing the tyre maybe enough.

mattr
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by mattr

TonyM wrote:
Mon May 28, 2018 5:22 pm
You have anyway to check the tension of your spokes regularly, especially if you ride a lot or ride on bad roads, descents etc.. It is for your own safety.
Same applies for all bolts etc.....I know so many stories of people not checking all these points and having all kinds of problems or even accidents and injuries.
Sounds like time for a new LBS then. I pretty much only ride average/poor roads and never check anything unless i'm doing "other" work on the bike. (it gets a visual check when cleaning obviously)
Wheels only get checked when i'm changing tyres, or if they've gone out of true..........

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Miller
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by Miller

jeanjacques wrote:
Tue May 29, 2018 8:17 am
Miller wrote:
Tue May 29, 2018 7:24 am
People, it's not about the precise spoke tension or headset adjustment.
But as Damon explained, if I understand right, tighten the headset "increase the system stiffness" and change the shimmy fequency.
Now it will occur at 30km/h for a more regular training :lol:
The headset has an optimal setting where it allows the steering to be free and without friction while not allowing any play in the bearings. Sure you can tighten the headset so that the steering gets tight but that will be annoying all the time and will make riding no-hands dangerous. Don't use the headset to correct some imagined problem with shimmy.

Shimmy is about system resonance where the system is bike+rider. What YOU do affects shimmy and as already mentioned, you can exclude it by adjusting your position on the bike.

alcatraz
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by alcatraz

I'm a bit amazed that so many people in this thread are willing to accept this phenomenon. It's not a vintage bike. It's an aeroad disc brake.

There must be something that can lessen the issue. I'd ask canyon directly. They might know which part is commonly the problem and maybe can help torque it better or something.

/a

Mr.Gib
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by Mr.Gib

alcatraz wrote:
Tue May 29, 2018 2:17 pm
I'm a bit amazed that so many people in this thread are willing to accept this phenomenon. It's not a vintage bike. It's an aeroad disc brake.

There must be something that can lessen the issue. I'd ask canyon directly. They might know which part is commonly the problem and maybe can help torque it better or something.

/a
But the rider is also a part of the system which is what makes this type of problem so vexing. Certain bikes with certain components, with a certain rider in a certain position can all add up to create a shimmy at certain speeds. Modern frames are much less prone to shimmy but if all the ingredients are just right, it can happen even if the equipment is all in good order.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

Hexsense
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by Hexsense

Question: if it's resonance of many equipment vibrate at synchronous frequency,
Would multi material on the system help?
Like fork, bar, steerer tube, rim are all carbon, alright. But instead of using carbon stem too we use aluminum stem which has different natural frequency.
Also, use bar from different company to the fork so eventhough both are carbon but they may have different resin and different natural frequency?

I heared on youtube there were a prototype airplane which happen to resonance with pilot's eyeball frequency. Render their eyes temporary unusable during landing/take off. The fixing is quite simple changing a small detail on the plane.

leandrofresh
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Joined: Mon Jul 13, 2015 12:45 am

by leandrofresh

Check this. You won't be able to fit it in an Aeroad, but for those who are experiencing it in other bikes. Cane Creek has the Viscoset, a headset with dampening technology to address issues like this.

https://blue.canecreek.com/products/headsets/viscoset

BTW: Now I recall that the aeroad has a setting in the fork to modify the trail. I don't know which one is the default position. Maybe you can switch it to the more relaxed position since I read somewhere that increasing the trail reduces chances of resonance.

by Weenie


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