Hmm... I'm not sure it's worth obsessing too much about overly defining railroad tracks in general. As JASP suggests, we have a very specific definition of the particular way the task will be done in our Rocky Mountain certification exams (see HERE
), but that's not to say that ours is the only way to do railroad tracks, or the only maneuver that qualifies for the name. If you leave two clean, parallel, arcing lines in the snow, I'd have to say it's railroad tracks of some sort!
In any case, to the point of the original post, there are a few reasons why the inside ski will diverge in railroad tracks (and other turns). Not all represent errors.
Perfect railroad tracks require very accurate and refined tipping of both skis to the precise degree each needs to carve its arc. This simple-looking task involves more skill than it might appear!
It's a common mistake to twist the inside ski while tipping it on edge. It's worth considering that any external rotation of the femur--inevitable with any amount of knee angulation of the inside leg--must be compensated for by internal
rotation of the foot and lower leg, and/or by increased countering of the pelvis. It's a complex movement, requiring highly evolved skills to get it just right.
But consider too that at least a little diverging of the inside ski tip is inevitable, and required--even when the skis remain "parallel"! Because the inside ski must inscribe a slightly smaller-radius circle than the outside ski, it must bend into a slightly tighter arc if it is to "pure carve" its turn. If the tips were even (no inside ski lead), both tip and tail of the inside ski would appear to diverge slightly due to this tighter bend. The wider the stance, the more this effect comes into play.
Add in a little inside ski lead, and the divergence will increase simply because the inside ski moves ahead of the outside ski. Being on two different points of the "circle," naturally the skis cannot point the same direction. The inside ski must diverge a bit.
Railroad tracks are "pure-carved" turns. There must be no skidding due to twisting either ski on the snow. But that doesn't mean that the inside ski will never diverge a little. It actually has to!