Ok - I edited my promise of that being the last post on the subject.
Not discussing it ... just to clarify what I am actually saying... and you are for/against...
If you read my back and forth with Tog, you will see that we/I agreed that zero is not easy, but just a mental cue, and the focus is simply on keeping the inside boot from shooting out ahead and you're pulling it back quite strongly to achieve that. And keeping a minimal lead is more important at the beginning of the turn and quite impossible after the apex, right ? (although still pulling it back has its advantages even there)
So when I look at this, I focus on the part before the apex all the way to the fall line.
To explain the bio-mechanics of this for TDK, it is simple:
Stand up, flex knees and keep shoes matched. Now invert the ankle of the left foot to the left and allow the knee to move left to simulate tipping. It works, quite a lot. Now shuffle the left foot forward one shoe length, without shuffling the hips. Now invert the same ankle and try to let that knee tip left. You will find that the range of motion is much reduced, as both the ankle and the knee are more locked than otherwise. This is why we try to pull the thing back as much as possible and why excessive lead leads to hip dump. Of course, there are other benefits I'm not getting into again.
This is also why you see sometimes more of tip lead in GS photos: you don't need that much finesse and quickness: you got speed and lots of time. In SL at the gate the turn is over - you realize that any photos there show the end of the turn, right? Also, in SL the boots are much stiffer and tight, so you don't have much room to play with.
How much? It depends on so many things: how flexed you are in transition versus how extended, steepness, timing, how much hip counter you have/need and a lot of stuff.
How much is good? Anything less than what it would be if you let it develop without effort. I don't even really look for zero tip lead, as I have said couple times already (it often doesn't matter where you are but how you got there).
If you think about it, because the forward angles of the boots is not much, simply touching the inside boot with the outside knee implies there is little tip lead, but if are to measure it you will find large differences between skiers and even the same skier, in different situations.
Maybe you should focus on finding other cues to analyze photos than just give up on 90% of the photos out there: I look for the effort to pull it back, which you can see from the relative difference in the angle of the tibia in any photo, from any angle: the relative angles of the two tibias are not affected as much by the photo angle, since they're always close to each-other.
In fact, in the Reilly shot I posted, you can clearly see the inside boot in the shadow of the outside boot, with that light from the side and also a huge difference in tibia angle and he goes on to execute a hip to snow slalom turn. As I said, it depends how much you need. I challenge anyone to do a hip to snow slalom turn without pulling back the inside foot strongly and prove me wrong that way. pretty please - until then, all this is rhetorical. (edit: it would be very interesting to see if one can hip dump one's way to the snow... I think I've seen some photos of such, but without being out of balance, I think it impossible).
You do realize that WC skiers are athletic beyond imagination and can achieve for instance counter on one single foot, from one single ankle? I and lesser skiers need all the help we can get...
p.s. having said all that, of course there should be ZERO tip lead. What, are you kidding me? Aim for anything more than that and you will end up with too much!
p.s.2 I agree that this is perhaps the most misunderstood element of high-end skiing, especially when we keep looking at photos of WC athletes. It's not just understanding what to do and when, but it's critical to understand HOW to do it, which exact muscles to use - use the wrong muscles and you're just destroyed your skiing, in which case you're better off not worrying about it.
Edited by razie - 5/4/15 at 8:39am