Hip width, shoulder width, toe width and anywhere in between or outside... how wide should you be on your skis?
A wide stance allows for good stability but it makes it harder to get on edge and it takes longer to cross your body over the skis. It is thus favored in speed disciplines, where turns are ample and take sufficient time.
A narrow stance offers less stability, but it makes it very fast and easy to switch edges and get the skis from one side of the body to the other. It is thus favored in technical, turny skiing.
Well, while the boots certainly should not get in the way of each other, many seem to favor a wide stance in all disciplines. That is rather limiting, obviously. People are built differently and need to do different things in different disciplines and different situations. Starting with slalom, which should have the narrowest stance and ending with downhill, with its wide stance, there is a multitude of widths that can be used.
The issue with using a wide stance is that balance tends to be distributed between both feet rather than concentrated on the one outside ski. I think of it as having the training wheels on.
I think this wide or athletic stance approach is a limiting factor in developing strong skiers. I think the roots of the wide stance approach are the "snow plow" position via which most people get acquainted with skiing, where a wider stance makes you feel more stable, but which has nothing to do with performance skiing and carving (which is on the outside ski).
When the words athletic stance are used, the analogy going through most people's minds is a soccer goalie or a Sumo wrestler and that's well, not what skiing is about! Skiing is about turning... so let's see how the narrow stance helps with that.
Consider that the effective canting, i.e. the "neutral" edge angle changes a lot with stance width.
WC skiers only seem to be in a "wide stance" during a tuck and now you know why.
Note that it is much easier in a narrow stance and you're more in balance than in a wide stance. In fact, with a wide stance you have to push the body from foot to foot, pushing yourself out of balance and spending more time out of balance and without control.
If this is not enough to get you to loosen up on a "wide stance" position, consider this: in technical skiing, we're supposed to have most of the weight on the outside ski, to improve grip! Why would the stance width even matter? How can it matter, since the inside ski has no weight, or minimal weight? What does "wide is stable" mean in this context?
Also, during the transition, the skis are un-weighted, so the argument that a wide stance helps you balance - in technical skiing - is wrong. They can't - skis are not supposed to be loaded in transition, are they? You are either extending (which is another discussion) or floating through to the next apex.
How narrow? Well, the skis should obviously not get in the way of each-other, so at least a few inches apart. How wide? Well, that's for you to discover, depending on your size, the speed, turning ability etc.
Some prefer to describe it as dynamic or functional. That is a reasonable message, although it doesn't actually specify anything, instruction-wise, if you think about it. Again, stance generally should be narrower in transition, to encourage weight transfer and edge shifting and improve balance.
So: stay narrower, but dynamic. You should explore all possible stance widths, find the extremes and start adjusting until you find what works for you in different conditions and, as you progress towards expert skiing, you will notice that a keen focus on balancing on the outside ski will result in a narrower stance.
Take a look at the various stance widths in this excellent video - keep watching his feet throughout:
Remember that the effective canting, i.e. the ability to ride a flat ski, varies a lot with stance width: the further the skis are apart, the harder or even impossible it is to keep them flat.
Boots are canted for only one stance width and, while certain variations are needed during all normal skiing, these cannot be too large or the canting becomes ineffective.
Otherwise, you only have to watch World Cup skiers carefully and maybe in slow motion: they generally have a narrow stance in transition and what seems like a wide stance during the turn, which in fact is not a wide stance. It is a narrow stance - what happens is that because of the inclination of the lower legs, the skis are separated in the same plane as the legs, not perpendicular to the legs, which is what stance width is about. Just look at it, carefully:
So: narrower in transition and get the feet apart at the apex with a pedalling motion (i.e. flexing), but have a dynamic stance.
My mantra has changed to "stay narrow and get on one ski". Balancing on one ski is much more important to performance skiing than any specific widths or positions.
For myself, I am working on consciously adjusting my width and error on the side of narrower, if anything. You see, many years ago, I thought that the pinnacle of skiing was to do short turns with the feet glued together (obviously carving is quite impossible).
Then, becoming a race coach, I went to the other extreme, and went to extreme effort to keep my feet apart and exaggerate that in order to learn it. Now I guess I found normality, which is... well, in between.
In fact, per CSCF, Canadian coaches should not prescribe a stance width. It's all about bio-mechanics and everyone has a different stance width that works for him/her in different circumstances.
What coaches should do is to explain the differences, make the athletes try different stances in different situations and help them find their own.
Also, it's important to note that hip width means that the second toe is under the center of the hip joint - I know there is some confusion there, but that's how the CSCF defines it. Go on, try it right now and get a feel for it.
In general, the stance should be narrow, with the feet under the hips, where they naturally tend to hang from the hips.
Talks and sessions to work on stance: