How I wish I could get my knee down
It is a mental thing. Go totally zen and it'll happen much easier than if you think about it. Here are the mechanics:
The position of your outside arm and outside leg are very important - they set you up for the turn.
As is your spine
The position of your butt is too.
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[*]First, align your spine with the center of the bike (so you're starting from the right spot), now, move your spine (start with your head) to the inside of the centerline (if your turning left, move your spine inside to the left)
[*]As you move your spine, your outside arm should relax and your forearm can lay on the tank
[*]Your outside leg, make sure your setting on the balls of your feet, pull your outside leg in and up so that the seat is sitting right behind your knee
[*]Lay your belly on the tank
[*]Pull your inside foot in so that you don't drag your shoes
[*]Put 1/2 of your butt ON the seat and the other half kinda hanging off
[*]At that point, you don't have to try to put the knee down, the knee will touch (or not) as you go through the turn (don't try this in bluejeans . . )
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Either way, you will have moved your CG lower and to the inside of the turn and your bike can go faster THROUGH the turn with less stress on the tires than it would if you were perched on top of the bike in 'standard seating' position.
The same turn, at the same speed, is actually safer if you have moved your weight lower and to the inside of the turn. This does NOT mean dragging a knee - just that being a dynamic part of the experience instead of statically sitting on top of the bike puts less demand on the tires, the suspension, etc. I know it sounds weird, but the lower and deeper you get your body in a turn the less the bike has to lean, the less lean, generally the more stable.