Hey Terry--hope you're okay first off. Speed wobbles are scary as heck. Second off, just as a courtesy to other readers, accidental caps lock (given the things you seem to want to capitalize are lower case) comes across as you using a megaphone directly into the side of someones ear. Not so pleasant. :)

(pretty sure tridork covered this but to reiterate)

First thing to check is that your front end is assembled and appropriately tight. Loosen that top-cap a smidge, loosen your stem/steer tube clamp bolts, snug up the top cap until it barely starts binding (steering gets a bit "tight") then back off an 1/8 of a turn or so, and tighten up your stem clamp bolts again.

Second, make sure your wheels are squarely mounted in the dropouts and the brakes are centered on the wheels. Yes, I've seen this happen, especially with zealous skewer clampers.

Third, wheels are true? Tires are installed nicely and in good shape? (deflate, walk around the rim pinching it inwards making sure that no tube accidentally snuck under the bead?)

Lastly, while riding, at good thing to do is unweight the saddle and pinch the top tube between your knees when going down hills (feet at 3 and 9 on the crank). This completely changes the resonance of the bike.

Hope these help!

---

The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important.

-Albert J. Nock

Things like valve stems have nothing to do with it.
All those little things are not root causes and the bike is always in such complex motion that without those little things the oscillation will happen because the system is unstable because of positive feedback.

The font wheel makes complex tracks and as it does the bike is lifted and lowered due to head angle and trail.
Fork blades and steerers flex and so do frames.
There are many small wobbles happening all the time, it's just when a few of them coincide and reinforce by all coming into phase together at certain speeds that troubles start.
Large changes in weight distribution can SOMETIMES set up a cancelling oscillation, much like you see damper weights on suspension bridges.
Changing tyre diametre changes the path the wheel describes on the ground and may also cancel or lessen the effect or even cancel it all together if it was a major contributor.
Clamping knees acts as a fluid damper.
Arms can be dampers or sometime contributors after it has started.
Changing the fork is the single most effective way to fix the problem, which indicates that the complex path the front wheel takes due to trail and head angle can be a majority contributor to the system, but not always as it can simply be fork flex.
Even stiffening the frame by adding a folding coupling can kill the problem, showing again that much of this is down to the major frame/fork design and not too much can be done by the end user.

You can be certain though, that valves, bearings, out of true wheels etc are minor contributors, very, very minor contributors.
Raising or lowering a stem is usually more effective than length changes.

Moving far forward almost always makes things worse by increasing forces and flex in the front end of the frame/fork.
The cure above of re-tensioning the spokes may simply have coincided with the user running lower tyre pressures or even a different size tyre.

The subject is way more complex than anybody so far can understand.
If somebody wants a good UNI project, please take this on, we are all curious to see a mathematical model that will predict this.

Interesting though is that it has never to my knowledge been experienced in the MTB world, even though speeds that some road bikes wobble at are easily reached.

While I agree with almost everything you mention, the OP has identified that the bike is fine with all other front wheels they have used. It's just with the one particular wheel that there is an issue.

While many of the small factors involved ARE very very small, it appears that in this case, with this front wheel, that they are conspiring to initiate an oscillation.

I did like that mention that mass can be a damper or a contributor. As this particular wheel sets up an oscillation (yet to be determined why) this may be triggering a change in the rider from damper to contributor.

IF like I do, the OP rides loose on the bike (for lack of better term), and the oscillation starts, then the natural reaction is to hold on tighter and change the rider from a damper to contributor (this is particularly the case if the rider tries to correct the oscillation. It's counter intuitive to consciously try to let go (not completely of course) when your brain screams to hold on for fear or getting launched off the bike.

We still need to find out what is happening with the front wheel on this particular bike to start the oscillation in the first place. Minor factors shouldn't be ignored. It's like sandpaper. One grain of sand makes arguably no difference. Many grains of sand make sandpaper and on a belt sander for example, they can make a huge impact.

If the problem ISN'T caused by the factors I mention, what do you think the cause of the initial oscillation might be. Clearly frame and headtube etc all remain unchanged, so let's leave those out of the discussion for now?

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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"

You can't leave frame etc out of the equation.
The oscillation may possibly only occur locally in the fork due to tyre diametre interacting with the head angle, but be amplified by the frame.
Changing either may be equally valid as a cure as the other.
It is very complex.
What we don't know from the posted information is the speed of onset, whether it is present in a mild form with different wheels or different tyres.

First try changing the tyre to a taller or lower one, or even ride at a much lower pressure.
The low pressure one is the obvious easy one to try.
It doesn't take much pressure change to change effective height of the wheel.
Then try slamming the stem if it isn't, or lift it if it is, to change the bending forces on the steerer.
You can flip the stem to regain original position.
You may also be able to try head tube extenders to lift the top bearing placement.

You can also try filling the tube partially with water and use a thick tube for a significant increase in wheel weight.
Use a standard run down a hill and note any change of speed of the initial onset to see if anything is changing and for clues as to which way to proceed.

There is also a slight chance that it is airflow induced, like the way the old HED trispoke used to get funny side pushes as a spoke went behind the extended aero forks and lost some side force in strong cross winds.
Different wheels may also have different centre of pressure and couple or not couple with with existing minor instabilities.

For example, in strong wind my Zipp 404's tend to make the front wander like I have a really flat tyre, but a set of Ksyrium SL's make the steering jerk violently and quite scarily side to side, even though they are a fraction of the depth.

See if you can find another wheel that shows some of the same problem and tease out the similarities.

This is a lot like a traffic accident, several things come together to create a situation and may be disrupted at different stages.
If the guy behind wasn't following too close at the same time as the guy in front braked late to head for an exit, then nothing untoward would have happened, but the two together create a problem.

Stem length? magnet? decals.? None of these things will cause it ....been riding for 30 years and never heard of it

Hi Terryl,

I have the same bike, but the lower end D-6 3.0, 2013 (red, black, & white) and love this bike, feels like I'm riding a rocket. I live in the foothills of SoCal and routinely hit 35+, 40.. and haven't experienced speed wobble. But I have the 60mm aluminum wheels, heavier than your composite wheels. To add to other responses, 30 mph is not that fast and if you are experience wobble each time, it could be a manufacturing flaw in the frame, a slight frame twist that places the the front and rear wheel out of alignment. Take to a bike shop that can measure the front and rear wheel track. If out of alignment, you may have a case to get a new, replacement frame from Fuji. Here's a good article on speed wobble from (what looks like) a respectable source: http://cyclingtips.com.au/...ike-shakes-its-head/

Good luck!

Stuart

The Fuji d6 still at Performance bike San Antonio, and still no news from them on what the cause of this problem is. The Fuji representative pretty much washed
hands of this frame and was told to take to Performance who sold it. After almost a month, no news, bike sitting there, local management does not seem to care or want to remedy the problem which from the post on this site, the frame has a problem with it. I did speak with local manager about refund and the 100 percent Performance guarantee. And still no final word from performance. I am waiting but seems they don't seem to care or want to honor the guarantee. Hoping to hear something soon.
Terry