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 Post subject: flexy bars
PostPosted: Tue Jun 19, 2012 8:33 pm 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
Hi.I put fsa k-light nano carbon bars on my Bianchi infinito and found when descending ventoux recently,with a very windy decent,coupled with xentis squad4.2s , that the wobble or oscillation that kept happening was very scary.the combination in normal conditions,eg no wind,was great.
The question is this.i know the wheels are far from perfect for the purpose but the bars seem very flexy, does anyone have any experience of the bars and if so, how do you find them?
Cheers.


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 Post subject: flexy bars
Posted: Tue Jun 19, 2012 8:33 pm 


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 Post subject: Speed Wobble
PostPosted: Tue Jun 19, 2012 9:04 pm 
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Joined: Fri May 25, 2012 6:02 pm
Posts: 81
Are you sure it was the bars? In other words, do you have a lot of experience at speed in gusty winds with the exact same setup EXCEPT that bars were different and never had a speed wobble issue? I ask because speed wobble issues are notoriously difficult to diagnose, because the bike/rider unit gets into a harmonic state where the wobble "builds" on itself, increasing in severity, as opposed to when the bike wobbles for a moment (perhaps even imperceptibly) and then recovers and acts normally. You may have "felt" the wobble in your bars (because it was the bars that were violently shaking your hands), but even bars that are "flexy" don't necessarily mean you will get a speed wobble riding them (though you certainly may) - it really could be anything from your wheels, frame, fork, headset, bars, and in many cases, riding position.

Here is a video of my last speed wobble - was only at 33 MPH but still not a lot of fun: https://vimeo.com/42816611. (wobble starts at about :40)

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S5 VWD | 9070 di2 | Rotor 3D+ SRM | Enve 6.7s
Cannondale SuperX Hi-Mod Disc | Sram Red | Rotor 3D+ SRM | Zipp 303s
P5 | 9070 di2 | TriRig Alpha/Sigma | Quarq Elsa | Zipp 808/Super 9 Disc
T1 | Scatto | Rolf Prima FX58/Zipp Super 9 Disc


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 Post subject: Re: flexy bars
PostPosted: Tue Jun 19, 2012 9:17 pm 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
hi.your wobble looks very much the same.i take your various points but i did the same decent in non windy conditions and the bike descended like a dream. I'm hoping that changing the bars will do the trick as it's the cheapest option.taking one bit of flex out the equation might work???!!!!


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 Post subject: Re: flexy bars
PostPosted: Tue Jun 19, 2012 10:24 pm 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
also the wobble was very evident at very low speed in very high cross winds at the top.so it's not just a speed thing although the wobble at 45 mph was quite horrific!!!!!


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 3:53 am 
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Joined: Sat Jun 13, 2009 4:02 am
Posts: 1960
Location: NoVA/DC
speed wobbles or "shimmy" is a harmonics situation, as you seem to be aware of. with that, changing almost anything in the bike/rider/road system to one that is noticeably different (size, stiffness, position, etc) will likely move the speed wobble. keep in mind that you could make things worse, or merely change the speed/conditions of its happening.
if youve never had this happen until you installed this bar, i'd change the bar as it seems the most sure-fire way of getting rid of the problem. but as i mentioned, you could go with a FLEXIER bar and it may also improve. you could also just try lowering the stem on your steerer with your current setup..


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 4:05 am 
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Joined: Fri May 25, 2012 6:02 pm
Posts: 81
jeza wrote:
also the wobble was very evident at very low speed in very high cross winds at the top.so it's not just a speed thing although the wobble at 45 mph was quite horrific!!!!!


Speed wobble at 45MPH? That's really scary stuff. Glad to know you are OK - that could have ended badly.

No reason not to swap out the bars and see if that helps. If not, you will want to systematically change one variable at a time on your bike until it goes away and you regain confidence on your bike.

_________________
S5 VWD | 9070 di2 | Rotor 3D+ SRM | Enve 6.7s
Cannondale SuperX Hi-Mod Disc | Sram Red | Rotor 3D+ SRM | Zipp 303s
P5 | 9070 di2 | TriRig Alpha/Sigma | Quarq Elsa | Zipp 808/Super 9 Disc
T1 | Scatto | Rolf Prima FX58/Zipp Super 9 Disc


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 4:11 am 
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Joined: Fri Mar 18, 2005 4:12 pm
Posts: 2308
Location: eh?
Small chance changing bars will help. Changing wheels (sorry) is a better bet. Some frames in some sizes with certain setups can be a problem.

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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 4:26 am 
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Joined: Wed Oct 31, 2007 10:32 pm
Posts: 7520
Location: Los Angeles / Glendale, California
Put your knee up against your top tube.
Wobble stops.

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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 6:16 am 
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Joined: Mon Aug 04, 2008 11:09 am
Posts: 327
Anecdote without any value :lol:

Five years ago I saw a Cannondale in the peleton develop a wobble. I could swear I saw the whole frame ripple, which is quite frankly impossible, so the wobble must have oscilated quite badly to give that impression. As if he were Moses the peleton split around him, everyone dove for safety :lol:


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 7:20 am 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
the whole bike is new so set up is as is.the bars are more flexi than i'd like so i'll change them and wait for it to happen again[or not] although i can't see me on a decent like ventoux to test it for a while unfortunately.


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 8:25 am 
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Joined: Wed Oct 06, 2004 6:55 pm
Posts: 1893
Location: Vienna, AUT
Why don't you post a few pictures of your bike and the current set up for us to review.


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 10:12 am 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
The piks are on the forum somewhere.

Sent from my GT-I9100 using Tapatalk 2


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 10:16 am 
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Joined: Thu Mar 18, 2010 6:37 pm
Posts: 61
Location: uk
If you look up...'infinito in Italian colours' ....

Sent from my GT-I9100 using Tapatalk 2


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 Post subject: Re: flexy bars
Posted: Wed Jun 20, 2012 10:16 am 


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 Post subject: Re: flexy bars
PostPosted: Wed Jun 20, 2012 8:16 pm 
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Joined: Fri Dec 24, 2010 9:37 pm
Posts: 560
Location: it's raining, it must be uk
tbh if it's the only time it's happened, i'd guess it was due to the wind

i had something that sounds similar on a road i've ridden many times before/since, the only difference that day was a strong crosswind, which was really unusual for the area

it started after a slight change in road direction (so wind angle changed too) and though scary wasn't a fullblown wobble, just felt like the front wheel was being shaken side to side, the bike itself seemed stable and both knees hard on the top tube didn't stop the wobble which surprised me, i was going over 70kph and it only stopped after i slowed to about 40kph

in retrospect i think maybe it was the same phenomenon that can affect chimneys etc. where a vortex breaks off alternate sides and drives an oscillation, but here it was the wheel doing it (deep rim)


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