Punishment for having CAPSLOCK turned on...

good one

Not unique to your bike, or that model, in all likelihood.

Lots of good info and hints on where to look for solutions in this article.

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Carl Matson

computer- wheel/spoke weight not mounted right,
weight is not opposite of the valve stem ?
causing wheel hop

forks/headset need to be snugged up ?

front wheel / axle not seated in forks correctly ?

tubes have too long of valve stem = heavy
and additional weight causes wheel hop.
so add weight/lead decals (get at tennis racket store) 3.00
to other side of rim to equal weight of valve stem
or get shorter valve stem tubes

these are long distance guess'

put bike in stand
and spin wheels fast
and see if bike hops erratically in stand

i ride an Orbea Ora (2008) with SRAM S80 rims. i encountered front-end wobble on a fast downhill when the S80 is mounted on the front. scared the shite out of me. i encounter this ONLY with this particular front wheel. i figured it to be the deep-dish nature and the air turbulence past it. so, unless i know i'm going to ride a fairly flat route, i leave that one at home.

i didn't see much reference on this topic as relates to the wheelset. anyone else have a situation similar to mine ?

For years I have read about people having these wobbles. Some people say it is caused by a frequency vibration. I be leave they are correct. Having ridden for more than 35 years on everything from a cannondale to a Colnago to my present Merckx I have never and I mean never had that wobble. I think it is because of position on a bike. If your position encourages the development of that particular frequency for that bike check your position. Move forward or backwards to redistribute your weight. Valves on a wheel won't cause what you are describing. And for the record I exceed 45-50 almost everyday on my training route.

like i said, the ONLY time i have EVER encountered this is on this particular bike (Orbea ORA) with the SRAM S80 front wheel installed, while in the aero bars. any other wheel and i'm golden.

+1

Which bike model, size and what wheels are you running? Also what height/weight are you?

Also, where did you buy it?

Wrong. I had a frame that wobbled and I regularly bomb down hills at 50MPh. Other riders of this frame also complained of the same thing, so it wasn't an isolated incident.

Easy to just say "wrong". Give a better explanation.

Very complicated and only slightly understood problem.
My current Scott can give a very small shimmy but only if I run the stem with one 10mm spacer under it.
Put the spacers in any other configuration and there is no sign of it.
Also gets worse the further back my weight goes, so only shows at high speed when my chin is down on the stem.

I have sat on a small girls bike that was simply horrendous and wobbled it's head off with every single person that tried it.
I don't know how that one ever got out of the shop.

You can try different spacers, stems, seat position and wheel weights.

All of which changes the harmonic frequency of the frame. I am just happy I have never encountered it. Sounds terrifying especially if you are zooming.

My last speed wobble was caused by the fort not being snugged with the headset.

My wife and I have the same bikes, different sizes, though, and same wheels, carbon clincher zipp 404s. I started to get wobbles at an alarming frequency, and I started getting them on my tt bike. I spoke to a Wheel Builder and he said spoke tension might be off. My wife's zipps were to spec, my two front wheels were not tensioned enough, even though they were true. I had the wheels retensioned. I haven't had one wobble since and have done numerous examples 45 to 50 mph descents. It's like I'm a brand new rider. Wobbles, are crazy scary.

Really?
If you know how unimportant spoke tension is to wheel stiffness you would understand why I ask.

I am 5'10' 180 and it's a 54 have been professionally fitted by Houston bike barn lady over off hwy 59
It has the shorter seat post
Originally purchased thru performance bike in San Antonio.
I have used these wheels on my Specialized Tarmac and hit 43 on descents and nothing
Not sure where to go with this!

well, for the benefit of us ignorants, why don't you dazzle us with your brilliant enlightenment ?

Yea, if the spoke tension was low enough to cause an issue, it would probably no longer be true. Because that means the spokes are loosing all tension during essentially normal riding.

Edit: I am betting the real cause was someone fixing the preload on the zipp hub.

It seems like you've isolated the cause of your wobble. That's great.

From my experience, something, (and there are lots of possible causes) starts an oscillation of some sort. This creates a nervous rider and that invariably leads to hanging on tighter. This generally makes the problem worse. When I ride downhill, I virtually don't hold on at all. My hands barely rest on the bars. I've hit some fairly large objects and never actually come off. Holding on tight makes the problem worse believe.

That said, since you've pretty much found the cause of your wheel issue, don't simply stop using that wheel, see what you can change to make the wheel usable again.

Others have suggested, but I'll re-iterate.

Valve weight can be enough to initiate a vibration. Use the shortest, lightest valve you can get away with.Take off the screw on thingy that keeps the valve tight in the hole (assuming you're using it).
Check wheel magnet location. Regardless of where it is, try it in other places. Trial and error will find a sweet spot.
Assuming clincher tires, make sure they're seated properly. I see quite a few people with incorrectly seated tires that in effect, create a hump on one side of the wheel.
Tires? flip them around, to relocate a possible heavy point of the tire. Same with a tube? Use a different (lighter?) tire. Powder your tubes and inside of the tire, so your tube and tire seat properly. Back in the day I didn't do this and once had a lump in my tire from a tube with a small fold! (yes I was in a hurry when I was installing it). Now I powder my tubes so they slide into the perfect position easier.
Wheel. Check the wheel itself. Is it straight and trued? Get it professionally tested. I had some HED3's and while they were within factory spec, the rear had a slight wobble built in it. It didn't cause me an issue, but I could feel it when going fast. Of course, with a HED3, there is no truing possible, but most wheels can be trued. Spin the wheel in a wheel jig to see if the wheel is out of balance.
Check wheel bearings are at the correct tightness. Even a slight looseness can start a vibration.

Finding a wheel imbalance fault can almost as hard as finding a squeak in ones bike. Annoyingly, just about every squeak in a bike sounds like its coming from the BB! Rarely does the squeak ever come from the BB :-)

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

The spoke tension on these wheels was about 1/3 below where it should have been per Zipp's guidelines. The wheel builder, who sells a ton of custom wheelsets per year, adjusted the tension a bit more than spec on every spoke. All I know is that has been the only change, and the handling and lack of wobble is exceptionally better when using the deep dish front- in my case. I'm very happy with the change- and it was literally overnight and instead of fearing descents, I've been attacking them, going for high speed records.

As to wheel stiffness, I understand that tension doesn't change it all that much, and I didn't mention that term in my post above. I'm only commenting on my shimmy/high speed wobble experience and what I did to solve it, and how it might be something to look at.

Most of the things you have mentioned there won't make one iota of difference if there is a true speed wobble.
Wheel bearings and valves pale into insignificance in the face of a proper oscillation.
Changing stack height usually works by changing the flex variables on the steerer and any wheel culprits are usually weight orientated or a change of tyre height changing the trail.
I have seen one bike where even a change of fork didn't cure it, and I would suspect in that case that it is a frame stiffness/damping issue.

Most people that say they have experienced speed wobble haven't and when they do get a chance to ride a problem bike will be amazed at the forces involved and it doesn't matter what you do, relax, dramatically change position, clamp the top tube with your knees etc, you simply cannot stop it.

An incorrectly fitted tyre is usually not noticed by a rider unless they can see a front tyre wobbling in front of their eyes.
Just the fact that the bike is in motion is enough to set off a wobble if it is inclined to do so.
Leave the screw on thingy on there, it will stop latex tubes from creaping around the valve stem and dying.

Any minor oscillation gets worse and worse, primarily due to the rider.

Sorta like the Tacoma Narrows bridge demonstrated, everything has its own natural frequency. Once an ever so slightly out of balance wheel gets an oscillation, it will get worse and worse.

The two ways to fix it (that I know of) are

1. prevent the initial oscillation (my previous suggestions were all about looking for the root cause)
2. change the natural frequency of the bike/rider combination. I usually do this by barely holding the bars so the bike can do its own thing. Another way is to change the natural frequency. Some have suggested sliding back on the seat (unloading the front wheel), or by clamping the top tube with your knees. When I've experienced speed wobbles, I usually do the top tube/knee trick as I've already done the other two.

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"