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PostPosted: Sun Dec 09, 2007 12:29 am 
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Hi guys, great forum.

I recently purchased a pair of Fulcrum Zeros from the LBS. They're light, fast, stiff, and alarmingly red. I weighed them on the digital scale and they were (f) 660g and (r) 870. Over their claimed weight, but that isn't bothering me much. Every aspect of these wheels is superb...

...with one glaring exception. At speeds from 5kph to around 30kph, and on the smoothest of roads, the rear wheel wobbles back and forth. It's enough to shake the chain, tool bottle, my calves, etc. In an attempt to fix things, I've:
Re-seated the tyres (both new, new tubes too)
Tightened the bearings around the axle
made sure the quick releases are done up properly
checked for loose, or turned, spokes, etc.

Do any of you have ANY idea what could be happening? My previous wheelset (SH-W601) didn't do it, and it is not the bike (Bianchi XL carbon). The rim is true and they're no flat spots. The mechanic suggested it may be the aero properties of the spokes - but at 5kph? I weigh 76kgs, FYI.

Cheers guys.

F.

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Posted: Sun Dec 09, 2007 12:29 am 


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PostPosted: Sun Dec 09, 2007 12:38 am 
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Location: Western Australia
That's God's way of telling you you should have bought handbuilts :lol:

My best guess is it's a freehub problem. Check that it's all tight, greased, blah blah blah.

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PostPosted: Sun Dec 09, 2007 12:52 am 
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Location: New York
The mechanic is a fool...

Take the wheel out and put it on a wheel stand. Spin it on the stand and get to the root of the problem.

If you don't have a wheel stand then use your hands.

Or take it back to a different LBS and have them check it out on the wheel stand.


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PostPosted: Sun Dec 09, 2007 1:09 am 
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Location: Lyon, France
And undo your tightened bearings again, before you kill them.

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PostPosted: Sun Dec 09, 2007 4:49 am 
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Location: New Zealand
Alarming shaking back and forth can only be imbalance.
Strip the tyre and tube and check to see if it still does it (a good set of wheels will only be out by a few grams and should spin well without the tyres on). Put a valve in the hole (or tape a similar sized mass over the hole....perhaps a small coin if your country has suitable sized small coins)
Retry....is the problem gone?
If it has...you have a poorly moulded tyre. They are not common, but they do happen.
Assuming it is the back one (surely you will have found any weight imbalance in the front, simply by seeing what part of the wheel stops down the bottom)...shift the chain out of the way and reclamp the back wheel in the frame. spin it.
With the chain out of the way (and therefore the freehub not ratcheting) the back wheel will be free to spin so you can find the heavy part of the wheel. Mark that part with a white board marker (erasable ).
re -install the tyre and tube....recheck. By now you will have your answer.

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PostPosted: Sun Dec 09, 2007 5:05 am 
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oh yeah.....and I agree with Stella-azzura....I think your mechanic is either pulling your leg , or he/she is less skilled than I'd like to have working on MY bike. I somehow doubt that fulcrum will let a spoke set, that could cause such an effect, be used for their better wheels. As far as I'm aware, fulcrum are a reputable company.
If it is imbalance...find a new mechanic (he/she is awful)
If it is an insecure free hub (unlikely but possible) put your mechanic on probation but give him another chance.
Since your vibration problem has a specific range of speed...I'm guessing at imbalance (sadly). There is a tiny possibility that the wheels are duds....I'm betting tyres and imbalance still tho : (

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PostPosted: Sun Dec 09, 2007 9:43 am 
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Location: Lyon, France
theremery wrote:
Alarming shaking back and forth can only be imbalance.

At 5km/h? Maybe at 80km/h, but it's simply not possible to build a bicycle wheel that far out of balance.

Try to get somebody to ride behind you to watch what is happening. My guess is that the spokes are very loose, so that although the wheels appear true when unloaded, as soon as you have some weight on them they are pulling sideways as some go loose under load.

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PostPosted: Sun Dec 09, 2007 10:21 am 
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Good point.(re.5 kmh). Does the wheel remain straight when it's being ridden, and does the shaking continue when the wheel is spun without weight on it? (i.e. in a stand)

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PostPosted: Sun Dec 09, 2007 11:12 pm 
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I'm taking the wheel in to the shop again this morning and I will run through all of your ideas. T

Thanks for all of your help, fellas, I'll let you know the outcome.

F.

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PostPosted: Mon Dec 10, 2007 4:24 am 
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very possible there could be a weight discrepancy in the rim itself, or the bearings could not be pressed all the way into the hub.

Spokes would be my first target though...


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PostPosted: Mon Dec 10, 2007 10:51 pm 
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Zeed wrote:
very possible there could be a weight discrepancy in the rim itself, or the bearings could not be pressed all the way into the hub.

Spokes would be my first target though...



I think you're right. I tested my bike with Ksyriums, Velomaxs and even a Fulcrum Racing One rear wheel (identical milling); none of the other wheels produced the same vibration.

The shop corrected the dish (which was out) but that only produced a more even vibration right through the speed range! The mechanic said that "the harmonic resonance produced by the wheel was overwhelming the outdated nature of my Bianchi" - I.e. THe BB was not stiff enough.

Hmm...

Anyway, I suspect I have a poorly milled rim (the Fulcrums have a lot of milling) and I'm heading in today to ask for a replacement.

I'll let you know of the outcome.

F.

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PostPosted: Mon Dec 10, 2007 11:08 pm 
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Feideaux wrote:

The shop corrected the dish (which was out) but that only produced a more even vibration right through the speed range! The mechanic said that "the harmonic resonance produced by the wheel was overwhelming the outdated nature of my Bianchi" - I.e. THe BB was not stiff enough.

Hmm...

F.


That mechanic is a trip... comical :lol:


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PostPosted: Tue Dec 11, 2007 12:32 am 
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Location: Lyon, France
Feideaux wrote:
The shop corrected the dish (which was out) but that only produced a more even vibration right through the speed range! The mechanic said that "the harmonic resonance produced by the wheel was overwhelming the outdated nature of my Bianchi" - I.e. THe BB was not stiff enough.

Hmm...

Anyway, I suspect I have a poorly milled rim (the Fulcrums have a lot of milling) and I'm heading in today to ask for a replacement.


I can't believe it's a design issue... they wouldn't be selling these things if they behaved like that.

Your mechanic is a fruit loop... it's either spokes or bearings. I did once have a harmonic vibration issue... but it was with a 6kg motorcycle race tyre, at speeds over 180km/h, resonating with 5mm of freeplay in the rear suspension. You really don't have the same amount of force at work :lol:

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PostPosted: Tue Dec 11, 2007 1:16 am 
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On the Racing Zero, I did have a tub that wasn't glued on right (actually a Deda Tre early version that had a high spot on the base tape near the valve), the effect it gave was the rear wheel 'chugging' along, both in sensation and sound - the riders around me could hear it. Tried regluing, and finally replaced the tire before the 'chugging' went away.


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PostPosted: Tue Dec 11, 2007 1:25 am 
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Sybarite wrote:
On the Racing Zero, I did have a tub that wasn't glued on right (actually a Deda Tre early version that had a high spot on the base tape near the valve), the effect it gave was the rear wheel 'chugging' along, both in sensation and sound - the riders around me could hear it. Tried regluing, and finally replaced the tire before the 'chugging' went away.


Yeah, tried a different tyre, still vibrated!!

Thanks

F.

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Posted: Tue Dec 11, 2007 1:25 am 


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