So getting back to tip lead. The femur rotation accounts for a little of the resulting tip lead, only if you in fact counter-rotate a lot, as you don't have to and in fact most ski square to the skis - even the racing photos - not all show a lot of hip counter-rotation: as it happens, at the apex, most are square to the skis, so no femur rotation. In fact, if you measure it, it could only account for about one inch, in most skiers. In fact, the femur rotation is in opposite directions at the top of the turn and at the bottom of the turn (i.e. skis point left at the top and they point right at the bottom) and the inside ski is still the one that leads. Ergo, we can forget about it and focus on the bigger cause.
The, in my mind bigger, cause is shortening the inside leg (and the changing slope angle throughout the turn, more at the bottom) so really the relative inclination of the skier relative to the snow (i.e. hip height and long leg). Let's look at the biomechanics of it, use plain physics and geometry: so put simply, the more the knee moves forward as a result of shortening, the more the ankle has to move forward with it. The resulting tip lead may be as much as a femur length, to keep the ankle flexing the same, which the boot shape enforces on you.
This is where it starts to get interesting. First with the inside foot: you can reign in the lead by pulling the heel back against the top of the boot, as much as you can given the forward flex and setup of the boot (tibia angle etch). Or just give up, let it shoot forward and stay on the back of the boot (too much lead). The pullback is useful if done with the right muscles, as it will be done against the hips, keeping the hips forward, but without rotating them or maybe even aid counter-rotating - this is the good one. The other one (that I did for one wasted season) was from the hips, pulling the entire hip back and rotating into the turn as a result (not to mention a lot of other bad effects like long legs and pushing and stuff).
The relative position of the outside foot makes a big difference, as well: it may be centered with no big pressure on either side of the cuff (fore/aft) which leads to a smaller lead. Or it may be back, with a lot of pressure on the front cuff, which usually means more resulting tip lead. Tactics dictates this part and we have seen every combination in the photos along this thread (and the other thread). On average, you'd be more centered at the apex and maybe more forward at the end, to tighten the turn and end it. Or, depending on the frame, you let the feet run ahead and so you're back but the leaning angle is gone now, or just hill-induced, so no big lead to worry about.
Counter-action of the hips is also relevant: as the inside hip moves forward from a square position, it tends to add to the lead (this is not femur rotation, it's on top or complementary, I guess). (as a side note, do you see why counter-action narrows the stance?).
And lastly, lifting the inside hip contributes marginally, by reducing the amount of shortening needed, so reducing the lead of the knee/ankle required. This is important for other reasons too though, so a focus on hips is beneficial. In fact, this was one of the hardest things for me to nail down: lifting the hip while managing the inside foot. This is why I'm big on exploring all forms of braquage to understand the relationships between upper body, hips and feet in many combinations.
This is why a good overall cue is inside boot somewhere under the outside knee - this accounts for the relative position of the outside ski, so this is what I am looking at, to gauge if a racer did ok:
1. The inside leg was shortened
2. The inside ski is away from under the body
3. The tip lead is under control.
The timing of this is important as well. If the foot shuffles ahead too early in the turn, when neither the inclination of the both skier and the hill warrants it, it is the fake counter and usually accompanied by a hip dump. Camera angle plays a big huge role though in gauging this - you have to always keep in mind that turns on the camera side look better than turns away from the camera (or vice-versa, I forget now).
Is that kind of logical and all-inclusive or did I forget something? You can see now why high-end skiing is quite freaking difficult and complicated, and for most, very opaque. You can certainly lay it out upfront and work on each of these individually or just reduce it to a subset of movements and refine them in time.
p.s. now - I will agree with you that this isimportant to racing and very high end skiing, but it's simple physics and bio-mechanics. If you in fact turn with the feet and attain big angles, where this stuff matters, or if you look at WC photos, definitely these are what you should take into account. I don't see why though this should not be relevant to all skiers trying to improve though?
note that I didn't prescribe any turn mechanics, I did not enforce any sequence of movements - I just dissected a turn at higher-angles and identified all the levers related to tip lead. What you choose to do with these levers is up to you, but certainly a predictor of the outcome of your turns.
Edited by razie - 4/26/15 at 12:04pm