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This is what I mean. Start at 2:38.
This happens because there is not enough trail, and because I've reduced the weight of the bike significantly. The rear of the bike is lifted 1" over the design spec with a 17" tire. It's lifted even more because I'm using a knobby 80 profile tire instead of the stock 70 profile tire. Then it's lifted further because I have the shock preload set very high. Finally, I removed the side cases and racks, which resulted in the center of gravity of the bike to shift slightly, and also the rear to ride higher. Lifting the suspension even more with my dogbone modification was enough to cause the bike to develop a high speed weave right around 70mph. Going back to stock fixed it.
To make a bike more stable, you increase the trail. The easiest way to do this is by putting a larger wheel or tire on the front, to raise the front end. To make a bike turn quicker, you'd generally lower the front end by raising the fork tubes up in the trees. Lowering the front end or raising the rear gives the bike a "flickable" feeling, at the expense of high-speed stability. There is only so high you can go before the trail is too short and a high speed weave can develop.
Charles.
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