mapep Posted January 21, 2009 Posted January 21, 2009 i won't mention a brand name, yet (an american brand), but it's a 10 speed with a semi compact crank (50/34 T), alu. with carbon stays & fork. When engaged in the biggest gear, 50/11, there is a noticable vibration on the pedals. This is the second new bike with the same problem, the bike rep., the shimano rep. & the head mechanic were unable to fix / resolve the original vibration problem & therefore replaced the entire bike. The shimano rep. reakons the casette, crank & chain need to be worn-in but that is such bullsh........!besides i've now done approx. 700 Km's & the vibration persists. Any comments, previous experience would be appreciated, ulimately the bike needs to be returned again, bought in November '08
turtlek Posted January 21, 2009 Posted January 21, 2009 is it while you are peddaling????? sorry might be a dumb question
mapep Posted January 21, 2009 Author Posted January 21, 2009 hey turtlek, no comment about the "dumb question", after all it's after 10pm, but thanks for the interest. Yes, my theory was the crank was not perfectly aligned with the frame @ 90 deg. & therefore when the chain was engaged the furtherest from the frame, ie the 50/11 gear, the error would be @ it's greatest. Just find it strange that this would be a problem with 2 brand new bikes !
Little-Ben Posted January 21, 2009 Posted January 21, 2009 crank probably not spaced properly or the chain could be gliding against the derailer causing a vibration to transfer into the frame and then the bb and then the crank, now that i completely drained my brain with useless info i think i will go to bed
mapep Posted January 21, 2009 Author Posted January 21, 2009 hey little ben, tried those options, put a da utra slim chain, different casette, checked adjustments, no joy !!! speak later
turtlek Posted January 21, 2009 Posted January 21, 2009 Mapep i have heard about a vibration caused while freewheeling downhill that the guy thought it was his pedals but ended up being his headset in the end thats why i asked have you checked that your front derailer is not touching on your chainring in any way through your pedal stroke and have you also checked that your front derailer is not under-tightened if it is a braze on derailer???
turtlek Posted January 21, 2009 Posted January 21, 2009 also another idea have you checked that your lockring is the right size lockring for the smallest cassette sprocket???
Johan Bornman Posted January 22, 2009 Posted January 22, 2009 Small sprockets do have a different feel to larger ones. If you look at the tooth design carefully, you'll figure out why. We don't ride in that gear forever so it is not a big deal. You say you think the BB is not aligned with the frame? That's easy to see with the eye or if you can't see it with the eye, put the bike sans wheels in a bike stand and wrap string from several fixed positions (not the fork all around the bike. This way it is easy to see if there is any a-symmetry on the frame. Frame-builders shudder when the string comes out. Thirdly, put the bike in a sturdy stand and slowly pedal in the offending gear. Is the frequency of vibration related to chain pitch? In other words, is there one vibration per link? Look for the chain rubbing aginst the no 2 sprocket when in the no 1 sprocket. If you can't see that, spray some market onto the sprockets and see where the chain rubs. Let us know what you find so that diagnostic session 2 can proceed.
Red Zone Posted January 22, 2009 Posted January 22, 2009 I find on all my bikes that there is normally one gear that causes a vibration through to the pedals when pedaling at a certain cadence. I assume that at a certain speed / cadence the chain builds up a wave pattern which starts to create a wave superposition which causes resonance in the frame and cranks which feeds back to the pedals.
Johan Bornman Posted January 22, 2009 Posted January 22, 2009 I find on all my bikes that there is normally one gear that causes a vibration through to the pedals when pedaling at a certain cadence. I assume that at a certain speed / cadence the chain builds up a wave pattern which starts to create a wave superposition which causes resonance in the frame and cranks which feeds back to the pedals. You've been reading too many hi-fi magazines. You are right about one gear that causes a vibration but the reason is much more innocuous though. It is simply that gear's tooth profile. It is easy to disprove the harmonious happy wave theory. Put the bike on a stand and pedal slower. The vibration persists. Pedal one link at a time. The vibration persists. Harmonious vibration needs energy. With a rampant standing wave significant energy is required before the wave starts to vibrate the number plates off the bike and this is not the case. Tooth profiles vary as the size of the sprocket varies and sometimes they simply don't engage as smoothly as the rest of them.
Wyatt Earp Posted January 22, 2009 Posted January 22, 2009 Harmonious vibration needs energy. With a rampant standing wave significant energy is required before the wave starts to vibrate These are known as nodes and are very common in lower frequencies, they actually resonate and build up massive deflective standing waves. In smaller spaces the nodes get bigger with every deflection and eventually becomes almost deafening, the only way to deal with this in concealed spaces is to use Helmholtz resonators or in some less extreme instances, traps. In open spaces they simply go from wave to ripple till they eventually die or should I rather say, they flatten out. I agree with you here Johan, I cannot see this theory being applied to bicycles.
mapep Posted January 22, 2009 Author Posted January 22, 2009 good day all, thanks for the tips & "engaging" replies, for a sec. i thought i was back in physic's 3 !will try out all the recomendations asap. One question i do need to open to the panel is this:- the vibration senario, is it common place & acceptable or do i persue the issue until it is resolved, that is if there is a solution to the problem ?Thanks again
Johan Bornman Posted January 22, 2009 Posted January 22, 2009 Don't worry about it. It is common and acceptable. No use having the rep break his head over it as well and you can only break in so many new horses before it gets boring. Go for a ride and enjoy the vibe.
Minion Posted January 22, 2009 Posted January 22, 2009 which causes resonance in the frame and cranks which feeds back to the pedals.I have experienced what, for want of further study, I will call resonance when using my bike on the IDT.I got vibration at one specific speed (~16km/h), regardless of the gear I was in. That fact that it occured only at one speed made me think of some kind of resonance. I believe it's got something to do with the wheel I use on the IDT, or possibly the IDT itself (or both) since it's gear-independent and doesn't seem to occur on the road.I played around a bit with speeds and gears at the time, but never really thought about it beyond that, so my theory could be completely off. Just some random ramblings, not entirely relevant to the original question.Edman2009-01-22 14:02:56
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