lilcliffy wrote: ...is the degree of heel lift on the rear foot...
(I am well aware that the conventional wisdom is to keep a compact stance, and reduce heel lift on the uphill/trailing foot.)
One of the typical reasons to poo-poo system bindings for telemark skiing is the notion that the toe-bar attachment encourages too much heel lift, and resultant lack of weight and control on the rear ski.
My personal experience is that without a heel cable, I cannot consistently keep my heel low on my rear foot, and I feel a very significant loss of downward force, when my heel is high. (When I don't need that power and control, it doesn't matter- but, when it does- boy does it matter!).
Well- here is a beautiful and very skilled Telemark skier, skiing with just 3-pins, and I see all kinds of heel lift...
Perhaps heel lift has very little to do with a toe bar vs. duckbill?
I’d suggest it’s all about pressure on the rear ski - being able to mash your ball of foot on to the rear ski and bring a large amount of your weight to bear down on the rear ski. “Stance” is critical, but only in combination with the boot flex at the ball of the foot and weighting. Heel lift is a function of all of this and how deep a turn you need or want.
You need a compact stance, as you and Al mention, in the sense that your back foot isn’t flailing around behind you - it should be under you. The rear foot should be vertically in line with your hips. If you were to compress completely, you would end up “sitting” with your butt cheek on the back spine of your boot. In that case, your front foot has slid forward as to be flat footed, with a sort of 90d at the knee and angle. The heuristic is to imagine dropping back on to your rear foot in a turn(emphasizes rear foot pressure) rather than stepping/sliding forward into a turn(which emphasizes front foot pressure).
The next thing you need is a boot/binging combination that lets you flex the boot in such a way that you can bear your weight down and mash the ball of your foot into the ski when you want that ski to flex, bite and turn.
A floppy to moderate stiff leather duck-billed boot allows you to do this, as the flex really only happens over the ball of your foot, and the the duck-bill, whether held by the three pins or cable, gives you the end-of-foot leverage to flex the boot properly, mashing your ball of foot under your weight, onto the ski.
With plastic boots it gets more complicated because the flex is so engineered. In a soft excursion/t4 with the duck-bill the flex is perfect when weighted, and even the binding doesn’t matter so much. As boots get stiffer in the sole flex, the more vertical terrain and aggressive skiing requires/delivers even more weight bearing down to flex and mash the ball of foot and pressure the rear ski, (a more active binding helps keep the ball of foot down too with stiff boots, but you still have to weight them).
NTN guarantees the ball of foot is stuck on the ski. The real secret though, is fighting for that rear-foot-under-you stance, and bearing your weight down on that ball of foot. NTN gives the impression of ball of foot pressure, but it really depends on whether you are bearing down on it or not, for good technique.
With NNN-BC, the problem is the relatively free pivot in combination with the often funky round flex of the molded sole - I find they lack that over the ball of the foot pivot point. It’s often not conducive to ball of foot pressure, particularly because there is no end of foot duck-bill to leverage. Heel lift can be pronounced without the benefit of ball-of-foot-pressure. It’s easy feel like your are on your toes. It’s for this reason that I still struggle with NNN-BC as a turning system.
Finally, with the proper stance and boot/binding flex, and weighting, the amount of heel lift will depend on how deep you want to turn. Heel lift without weighting & mashing your ball of foot into the ski is bad. Lots of weight over the rear foot, and a lifting heel as you mash your foot into the ski is good. How low you go and how much your heel lifts depends on how deep and hard a turn you want. Imagine your legs are a compression spring, the more you compress them, the more energy is transferred into the turn. As Harris pointed out, on easy terrain an upright/low heel lift turn is fine, but in more aggressive skiing deeper turning pressure is called for.
This isn’t a great gif, but you might see some good heel lift with my back foot under a vertical line down my back, under my weight, as I go by.
