The "WOBBLE"
My 1st experience with the death wobble was October of 2011 out on a training ride in lake Mead national park in Boulder City Nevada. Descending down a hill with an 8% grade for ¾ of a mile with an easy left turn then you start to make your way up another hill. I have done this many times before and no wobble. To add to my nearly sh*!ing myself 
as a car goes by me while ridding out the death wobble. Took the bike into the LBS told them what had happened to me and asked if my wheels were ok and they were. In the last week I have experienced this twice. I ride a Cervelo P3. None of the times the wobble attacked have I had a hydration system up front. The one thing that has been congruent is that I get a gut feeling (meaning that I feel unsafe and not confident in my abilities) that something is wrong and I go from the arrow position to setting up on the hoods to slow down then the wobble attacks. My follow up question is how does one get over the mental aspect of going fast but in a controlled state when descending after experiencing the death WOBBLE? Now I'm gun shy and not ridding to my potential.
Comments
I can't speak for the mental aspect of it. I went bombing down one hill at 51mph at the Syracuse 70.3 and had the time of my life doing it. I passed plenty of people braking down the hill. I didn't have a wobble to deal with though.
I'm not sure the extra couple of pounds of weight from a front hydration system would cause the issue but I'm just speculating. After all, you can have differing amounts of body weight distribution on the front end depending on your position. I can guarantee that is much more weight and force than a bottle.
Wobble is no fun! I crashed badly due to high speed wobble. Never really did figure out what caused it. I posted in the forms, got lots of good ideas and summarized them in an email to my LBS so they could do a complete look at the bike. Bottom line is the bike checked out OK, I still ride the bike and wheels. My summary:
Tom
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What is the cause of these high speed vibrations? My engineering based opinion is 1) it is not user error generated. 2) Harmonic vibration is the likely the cause. The rotating front wheel is natively out of balance due to the valve stem. 99% of the riders don’t add weight on the other side of the rim to balance for this weigh imbalance. Think what we do to our car wheels.
Ok so now you have a rotating system with a native unbalance to it. You mount that in a front fork on a bike which is a long thin structure set to hold the wheel. In my view all mechanical stems like this have a situation when then can vibrate at a harmonic frequency. This is where heavy vibration occurs with minimal input of energy. Think of a tuning fork – when you hit it, it rings at its harmonic frequency , and rings for quite a while. My view is you and I hit that harmonic frequency on our down hills – it takes just the right speed to set it off then bang it is there. This is not something that 2 mph slower is 40 % less vibration. At that speed it doesn’t happen. BUT once it is started it can continue to resonate through a surprising change in speed – so slowing down 10-20 % did not stop it.
Summary Tom this was not operator error in my view. The solution is to review the overall trueness and balance of your front wheel. The more balanced you can make it in all respects the higher the speed where a harmonic will occurs and also the less energy that the harmonic will demonstrate.
I have experienced the power of what energy is present when a rotating mass goes though a harmonic frequency in other situations than on a bike. My first job out of collage was in the design and manufacture of power plant size turbines and generators. These large rotating machines spin at 3600 revolutions per minute. They would go through a painstaking process to balance these machines in 3 axis. Once they were within specified balance specifications they would be spun up to operational speed. Even with a balanced machine you could feel it got through its harmonics over a foot ball field away in the building.
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Have your LBS check the cones on the wheels.
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I had the same terrifying thing happen to me on Ride the Rockies a few years ago. I love to downhill, and I'm usually pretty fast. However, on some of the long mountain descents, I started to feel uncontrollable shimmying. I ended up talking to the Mavic support guys who work at RTR. They suggested that my shimmy was caused by using a 404 for my back wheel. Even though I was using a narrow rim on the front, they argued that winds hitting the back wheel were causing the shimmy to start. They lent me some Ksyriums, and I didn't have any more problems.
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This maybe very simplistic but I remember during the Northeast century ride last year, Mike had a wobble and it turned out to be his front wheel wasn't tightened sufficiently. I wonder if there is something going on with your skewer or the springs where they feel secure when you place the wheel on, but they actually loosen for some reason once you start riding
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Tom, I would definitely look into the mechanical solutions first: have the frame, wheels, headset, etc looked at.
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Tom – As all have pointed to above. The mechanical system that went into the harmonic condition includes the wheel, tire, Hub (cones), forks head set, frame alignment front to back …. All of the elements interact with each other and will vibrate at some harmonic frequency if conditions are right. There may not be one single item that is the culprit. As Rich said have the mechanical system gone over top to bottom.
On wheel balancing – focus primarily on the trueness of the wheel – sided to side and roundness. The valve stem weight issue I pointed to was mainly to say that the rotation system we all ride is natively unbalanced. If the other elements in your system are solid , I would not worry about the valve stem. On metal rims the joint where the rim connects to its self is often a heavier point than the valve stem. If you want to balance these weight issues out, I have seen a couple of approaches used. One is to use small wraps of lead soldier added to the spokes. Another is sand added to epoxy and this pasted on the rim to add weight to the light side. This is often done on carbon rims.
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The wobble is usually a mechanical issue. Sometimes this is a bike issue, sometimes it is just the natural forces at work on the bike. It can be a combination of aerodynamics, wheel balance, steerer alignment, frame alignment, road surface, weight distribution, etc... At one point or another everyone runs into this issue. On my road bike I can have issues once I get above 45 miles an hour on a windy day. On our tandem it seems to develop above 60 miles an hour.
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As Rich mentioned, first have the bike looked at to make sure there are no structural issues. If everything checks out, there are a number of things that you can do to lessen the impact. You already mentioned clamping your knees to the top tube. A couple of other things to try if you begin to notice the front end of the bike vibrating.
- Start peddling again. By maintaining a constant cadance on the bike you can counteract some of the issue with the front end. You just need to slow peddle soemto pick up the gyroscopic effect.
- Come out of the drops and move your hands to the brake hoods. Being in the drops forces your arms to be more rigid which transmits the vibration into your upper body and just reinforces the vibration and results in instability. This is one of the issues with a Tri bike. The brake hoods are a little farther forward and force your arms into this stiff position. The important thing is to relax your arms and upper body so that they absorb the vibration and dampen the effect.
- Adjust your position on the saddle. Sometimes you may have to move forward on the saddle, or back on the saddle. See what will help, For me I tend to move back off the saddle. I know others that feel more comfortable moving forward.
If you feel like you are getting out of control and freaked out, the first thing to do is sit up. This is the bike equivalent of pulling the parashoot. It will help to either slow you down, or slow down how quickly you are accelerating. You can also rotate your knees out to increase the surface area. Think of this as going anti-aero.
Start applying the back brake. Don't slam it, just slowly apply it. If you are using cork brake pads with a carbon rim this probably won't help much. Then you can start to feather the front brakes to further retard your speed. Again, do not slam on the front brakes or use them to heavily. There is very little weight on the front wheel and they will lock up easily causing you to flip over or lose control of the front end.
A couple of important things to keep in mind. DON'T PANIC. The bike wants to stay up as much as you do. A properly adjusted bike will naturally remain upright. Keep your upper body loose, it is your shock absorber. If you tense up your arms, the front end of the bike will become much harder to control.
Point is nothing wrong with the bike or wheels. I chose to NOT ride it that fast and just sold it. Get another bike sell yours on ebay the vairables trying to figure this out may well bust you up.
Have had wobble problems often.
6 foot 6 inches does not help.
my recent issue was due to hed h3 on the front. changing to mavic cosmic cabones solved.
yes time trial bikes more unstable on the hoods versus down in the aero bars.
for me, state of mind helps. If I am relaxed, no problems. If I am tense, problems.
work on the Rich Rules. Find his wiki on decending.
@ Tom Glynn sorry to hear about that crash.
@ Coach P I went to a Retule bike fitter shortly after I bought the bike. found the wiki on descending!!!!
I feel that I'm armed with some great info on keeping the rubber side down.
Thank you all for your input & will keep you up to date with the "WOBBLE"