Shakes on descents with 404
#26
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I can't believe that people are trying to say that an unbalanced wheel can't cause the bike to shake at high speeds. I made a video of my bike's rear wheel spinning down from about 40 mph. This is a heavy reynolds assault clincher rim with a michelin pro 4 tire, vittoria latex tube, and a light hollow valve extender. A lighter rim would shake much more and the effect would be doubled with two wheels spinning. In the video the bike is securely attached to a sturdy stand.
Unbalanced Reynolds Assault Clincher - YouTube
Unbalanced Reynolds Assault Clincher - YouTube
As I said before, I'm not saying it isn't true, only that I'm surprised if it is, because the weight we're talking about for a valve stem, even an 80mm one, I'd think would be too little. But hey, if you're saying that the effect you experienced in the video was due only to valve stem (what length?), and not manufacturing issues in the tube, tire, or rim, then I guess I need to reevaluate my ideas.
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I can't believe that people are trying to say that an unbalanced wheel can't cause the bike to shake at high speeds. I made a video of my bike's rear wheel spinning down from about 40 mph. This is a heavy reynolds assault clincher rim with a michelin pro 4 tire, vittoria latex tube, and a light hollow valve extender. A lighter rim would shake much more and the effect would be doubled with two wheels spinning. In the video the bike is securely attached to a sturdy stand.
Unbalanced Reynolds Assault Clincher - YouTube
Unbalanced Reynolds Assault Clincher - YouTube
On a workstand there is nothing to resist it, so even a tiny unbalance appears significant.
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#28
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Hi thanks for the video. Exactly what i have happening on my bike when i spin the wheels on the stand.
Now from the advice here. If i were to find a way to balance the weight, would i see the difference when spinning the wheels on the stand?
thanks
Now from the advice here. If i were to find a way to balance the weight, would i see the difference when spinning the wheels on the stand?
thanks
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I can't believe that people are trying to say that an unbalanced wheel can't cause the bike to shake at high speeds. I made a video of my bike's rear wheel spinning down from about 40 mph. This is a heavy reynolds assault clincher rim with a michelin pro 4 tire, vittoria latex tube, and a light hollow valve extender. A lighter rim would shake much more and the effect would be doubled with two wheels spinning. In the video the bike is securely attached to a sturdy stand.
Unbalanced Reynolds Assault Clincher - YouTube
Unbalanced Reynolds Assault Clincher - YouTube
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My carbon tubulars do that. I have never considered "fixing" it.
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Last edited by Homebrew01; 06-15-14 at 02:51 PM.
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All carbon wheels will do this unless the manufacturer added weight on the opposite side of the valve stem. I am not aware of any that do, however some might. It's much less noticeable on aluminum wheels because the valve is opposit of the rim joint, which is the heaviest spot on rim. Carbon rims don't have a heavy spot. Also the valve makes up a higher percentage of rotating weight on a light rim.
I don't ride much in the mountains so I've never bothered to balance my wheels. I can defiantly feel a shimmy at 35 mph and above but it doesn't bother me enough to do anything about it. I don't understand why everybody is so butthurt in this thread. I don't think any of the doubters own a set of light carbon wheels, or they live somewhere flat and never see sustained high speeds.
I don't ride much in the mountains so I've never bothered to balance my wheels. I can defiantly feel a shimmy at 35 mph and above but it doesn't bother me enough to do anything about it. I don't understand why everybody is so butthurt in this thread. I don't think any of the doubters own a set of light carbon wheels, or they live somewhere flat and never see sustained high speeds.
Last edited by Trucker Dan; 06-15-14 at 02:32 PM.
#32
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OP, just try adding some weight opposite the valve stem. See if it works. It would take 30 seconds to try.
As others have said, it's more likely that you're either misinterpreting more pronounced effects of the wind or something is out of adjustment.
As others have said, it's more likely that you're either misinterpreting more pronounced effects of the wind or something is out of adjustment.
#33
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The day i did the descent was a very windy day. Going direct into head wind and a cross wind at same time at 75km on a descent.
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If that's the cause, it all gets very specific and down to grams, stuff you've not discussed specifically or convincingly, which is why I'm so dissatisfied with your valve stem weight hypothesis as an explanation for the OP's bar shake. Again, may be true, but I just want a little better understanding of why it's happening in this case.
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All carbon wheels will do this unless the manufacturer added weight on the opposite side of the valve stem. I am not aware of any that do, however some might. It's much less noticeable on aluminum wheels because the valve is opposit of the rim joint, which is the heaviest spot on rim. Carbon rims don't have a heavy spot. Also the valve makes up a higher percentage of rotating weight on a light rim.
I don't ride much in the mountains so I've never bothered to balance my wheels. I can defiantly feel a shimmy at 35 mph and above but it doesn't bother me enough to do anything about it. I don't understand why everybody is so butthurt in this thread. I don't think any of the doubters own a set of light carbon wheels, or they live somewhere flat and never see sustained high speeds.
I don't ride much in the mountains so I've never bothered to balance my wheels. I can defiantly feel a shimmy at 35 mph and above but it doesn't bother me enough to do anything about it. I don't understand why everybody is so butthurt in this thread. I don't think any of the doubters own a set of light carbon wheels, or they live somewhere flat and never see sustained high speeds.
The wobbles come and go. The valve stem is there all the time.
We're not butthurt. We're telling you that you're wrong.
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I've got two sets of Zipp 202 clinchers and another set of 38mm generic Chinese carbon wheels. Probably over 7000 miles accumulated. I've yet to experience this phenomenon.
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Someone do the math. How much outward (upward) force does a valve stem exert when riding at 50 mph ?
It would have to be lot to counteract the weight (downward force) of rider and bike to the degree that it is noticable.
It would have to be lot to counteract the weight (downward force) of rider and bike to the degree that it is noticable.
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Again, what are you saying? All carbon wheels will cause front end shimmy at high speeds? Obviously that's wrong, right? And, let's not forget that the 404s are not some super light wheel set-- it's 1640gm-- and it's not a carbon wheel set; it uses a carbon fairing bonded to an aluminum rim, which presumably, is held together at the joint as any alu rim is, which is going to add weight whether it's sleeved or pinned or welded.
If that's the cause, it all gets very specific and down to grams, stuff you've not discussed specifically or convincingly, which is why I'm so dissatisfied with your valve stem weight hypothesis as an explanation for the OP's bar shake. Again, may be true, but I just want a little better understanding of why it's happening in this case.
If that's the cause, it all gets very specific and down to grams, stuff you've not discussed specifically or convincingly, which is why I'm so dissatisfied with your valve stem weight hypothesis as an explanation for the OP's bar shake. Again, may be true, but I just want a little better understanding of why it's happening in this case.
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Do you live somewhere where you get up to 40 mph coasting? It's not a hard vibration but it's there. It's light enough that if you are pedaling in a sprint you probably wouldn't notice it. I've noticed it on all my carbon wheels on several different bikes. I have a set of Reynolds dv46 tubular, Reynolds assault clinchers, and neuvation carbon tubulars. The Reynolds tubulars are the worst because they are the lightest. I would have posted a vid with those instead of the assaults but they have cross tires glued on right now.
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Car wheels/tires are balanced to within 1/4 ounce. That's 7 grams, about the weight of a 80mm presta valve. If you can feel 7 grams on a 60 lb car wheel, what's it going to feel like on a 2 lb bike wheel.
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Cars have suspensions. Different scenario.
You won't feel it on a car either, but it could affect tire wear, if the wheel slightly unweights every revolution.
You won't feel it on a car either, but it could affect tire wear, if the wheel slightly unweights every revolution.
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Last edited by Homebrew01; 06-15-14 at 09:17 PM.
#42
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I suspect a cascade of issues causing your speed wobble. Resonant frequency due to the wind/speed/yaw angle of the bike and rider system, wheel balance (I'm with TruckerDan on this) and bearing play. Focus on correcting one issue at a time and testing. Let us know how you make out.
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And for the non-mortals? If it's such a big deal, why don't the pros who descend at over 60 mph bother to counterbalance the valve stem on their wheels?
Bikes have been around for over 100 years, and you're the first one to think this is a huge deal? When no one else does?
What are the odds?
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I have a pair of 404's tubulars and don't experience what the OP is talking about. I'll feel the front wheel push on a strong gust of wind...but otherwise I don't get any kind of front end shimmies. Only time I've ever felt a lump in my tire is when it wasn't seated properly at the valve stem.
#47
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If the OP is only experiencing the phenomenon, as they said on windy downhills, then wind is probably the correct answer.
If it happens all the time, it's probably a maladjustment of bearings, skewer, etc.
If everything is adjusted properly and it still happens, it's probably a bad tire, or improper spoke tension.
If those things are right and it still happens, it's probably the valve stem ( ), and the wheel should be sent to GS Astuto in Tokyo for dynamic balancing: Truspin? by GS Astuto
In fact, we should probably send our wheels in for a Truespin to pickup those extra 5-7 watts PER WHEEL! Hot damn, non?
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I hope the OP has taken his wheel to his LBS...and if they can't figure it out...they can send the wheel back to ZIPP to get it checked out.
Last edited by I <3 Robots; 06-16-14 at 02:41 PM.
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Getting back to valve stems, I notice that my carbon wheels will come to rest from spinning with the 80 mm valve stem up in the 2 or 3 o'clock position (after some back and forth rocking). Another data point.
#50
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When i spin my rims on the Stand. The valve stems both on front and back always come to rest at the 6 o clock position. so indicates i assume weight is heaviest at valve stem? as i use 80 mm tubes. the rims are clincher?
so should i put some weight opposite to that then?
so should i put some weight opposite to that then?