Originally Posted by rpenmanparker

While it is impossible to know for sure, speed wobble (or death wobble) is usually not the fault of a wheel or any other individual part of a bike, but rather a systemic failure of the entire bicycle. Various stiffness characteristics (or the opposite -flexibility), weight distribution, vibrations from the road, speed, etc, all combine to produce the resonant harmonic vibration that results in the catastrophic outcome. It is not thought to result from something being loose like a headset or hubs. In fact things being too tight can be a contributing cause since that allows the vibration to be transmitted undamped throughout the frame. The best analogy for it is the catastrophic failure of a bridge when an army is crossing it in lockstep or when a windstorm starts it vibrating. There is just a resonant frequency that when reached throws the structure into violent oscillation.

The one corrective action that is routinely recommended is to clamp the top tube between your thighs to dampen the vibration before it gets out of hand. Of course that is a lot harder these days than in the past due to sloping top tubes.

There is no way to test a bike for this characteristic a priori, because you can't predict what frequency it will take to start the oscillation. Some say too much trail is a cause, others say too little.
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here is an article by Jobst Brandt about it: Shimmy or Speed Wobble by Jobst Brandt