flexy bars

Discuss light weight issues concerning road bikes & parts.
Post Reply
jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

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.

by Weenie


refthimos
Posts: 104
Joined: Fri May 25, 2012 6:02 pm

by refthimos

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)
EVO Hi-Mod | 9070 Di2 | Rotor 2Inpower | Aeolus TLR 3/5
P5 | 9070 Di2 | Rotor 2Inpower | Aeolus TLR 7
T1 | Power2Max Type S | Rolf Prima FX58/Zipp Super 9 Disc
SuperX Hi-Mod Disc | Sram Red | Power2Max NG

jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

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???!!!!

jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

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!!!!!

thisisatest
Shop Owner
Posts: 1980
Joined: Sat Jun 13, 2009 4:02 am
Location: NoVA/DC

by thisisatest

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..

refthimos
Posts: 104
Joined: Fri May 25, 2012 6:02 pm

by refthimos

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.
EVO Hi-Mod | 9070 Di2 | Rotor 2Inpower | Aeolus TLR 3/5
P5 | 9070 Di2 | Rotor 2Inpower | Aeolus TLR 7
T1 | Power2Max Type S | Rolf Prima FX58/Zipp Super 9 Disc
SuperX Hi-Mod Disc | Sram Red | Power2Max NG

Mr.Gib
Posts: 3063
Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

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.
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.

User avatar
prendrefeu
Posts: 8608
Joined: Wed Oct 31, 2007 10:32 pm
Location: Los Feliz, Los Angeles, California
Contact:

by prendrefeu

Put your knee up against your top tube.
Wobble stops.
Exp001 || Other projects in the works.

Franklin
Posts: 400
Joined: Mon Aug 04, 2008 11:09 am

by Franklin

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:

jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

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.

User avatar
Stolichnaya
Posts: 2615
Joined: Wed Oct 06, 2004 6:55 pm
Location: Vienna, AUT

by Stolichnaya

Why don't you post a few pictures of your bike and the current set up for us to review.

jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

The piks are on the forum somewhere.

Sent from my GT-I9100 using Tapatalk 2

jeza
Posts: 63
Joined: Thu Mar 18, 2010 6:37 pm
Location: uk

by jeza

If you look up...'infinito in Italian colours' ....

Sent from my GT-I9100 using Tapatalk 2

sungod
Posts: 1462
Joined: Fri Dec 24, 2010 9:37 pm
Location: it's raining, it must be uk

by sungod

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)

by Weenie


Post Reply
  • Similar Topics
    Replies
    Views
    Last post