You could trying getting forward more on the bike.
You should decsend in the drops cause it helps get more weight over the front wheel and lowers the center of gravity..
You could always get a parlee that'll fix the problem..

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Skunkworks Bikes

not to beat a dead horse, but rake is the distance the front axle is from the steering axis. just because the fork legs are "straight" or "curved" means nothing. what matters is where the axle ends up.
trail is the distance the tire contact patch is from the steering axis.
please look at eric's diagram again. note that, even though the fork pictured is curved, one could draw a straight line from the head tube to the axle and it would still have the same rake (and trail)

It could be worth going over to the VeloNews archives for Lenard Zinn's tech articles - he's covered this topic, and is a bit of an expert on big frames.

Judging by that video there must be different kinds of shimmy.

The violent shaking that I've experienced would not be cured by hands on bars like that.

The last time it happened to me was with my Supersix, on which previously I'd had no problems decending at all. Then I'm on a descent when buffeting crosswinds hit, and sure enough the whole bike's shaking. I'm in the drops, relaxed. All I can do is hang on and try to slow down.

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There's sometimes a buggy.
How many drivers does a buggy have?

One.

So let's just say I'm drivin' this buggy...
and if you fix your attitude you can ride along with me.

http://www.youtube.com/watch?v=GekiIMh4ZkM

slow down

I have tweaked my position over time, and like it a lot now. Also tried most of the points brought up so far, unfortunately to no avail.

My bike is a Kuota Kharma Ultralite edition, which has a 73° HT angle, and an 48mm rake. Could it be that the 3mm extra rake over the standard edition make it (so much more) twitchy?.

Here's a picture, please ignore the fact that I'm testing a non-matching saddle at the moment ...

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Bikes: Raw Ti, 650b flatbar CX