chaadster

Saying an unbalanced wheel would cause a bike to shake is one thing, but saying a wheel unbalanced because of a valve stem would cause the bike to shake so violently one has to hold on tighter, is saying something else, i think.

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.

Homebrew01

Workstand <> real world on the road riding.
On a workstand there is nothing to resist it, so even a tiny unbalance appears significant.

CanadianBiker32

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

gc3

Sample size = 1

Homebrew01

I suppose, if "performance" on a workstand is important to you, go for it.

My carbon tubulars do that. I have never considered "fixing" it.

Trucker Dan

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.

DXchulo

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.

CanadianBiker32

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.

chaadster

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.

achoo

If what you say is true, none of the methods of dealing with a speed wobble would work. Tjhey do work. And the wobble from the valve stem - if it were really there when you ride - would be perceptible all the time. It isn't.

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.

gc3

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.

Homebrew01

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.

Trucker Dan

404s clinchers have been full carbon since the firecrest wheels came out in 2012.

Trucker Dan

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.

Trucker Dan

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.

Homebrew01

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.

pdedes

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.

gc3

No mountains here but plenty of hills where I approach or exceed 40 mph with some regularity....

achoo

A LOT less - bike wheels are bigger so they turn slower. Bikes go a lot slower, too, at least for us mortals. And radial acceleration is proportional to rotational speed squared.

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?

achoo

Also, forces from the valve stem, however small they may be, are directly in the wheel plane and will not induce any side-to-side wobble.

I <3 Robots

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.

chaadster

And this brings us back, full round, to post #10 by Carpediemracing, which said that in windy conditions, some shimmy is normal.

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?

I <3 Robots

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.

springs

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.

CanadianBiker32

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?