Ditto on the saddle issue... Everything works together to produce ideal body mechanics, smooth pedal strokes, stable core... But it would be tough to keep your hips and core stable if they weren't positioned right. When I first got my roadbike, after a bit I notice that I too wobbled when I got into higher RPMs... I took it in to the shop and he tweaked my saddle height. I don't remember which way it went though. I don't wobble any more.