Boot board /Ramp angle.
This aspect of boot geometry is responsible in large part for the greater number of those skiers who appear to be ‘in the back seat’. This is what the casual observer will notice if the ramp angle is too steep for the observed skier’s skeletal structure and the way it stacks up.
Basic math indicates that when you apply a defined ‘load’ to an inclined plane, a greater proportion will be directed to the ‘narrow’ end of the incline. This can be useful in controlling where and how a ski is bent into reverse camber, relative to the athlete’s CM. However, if the incline is too great, the athlete will tend to topple forward in the absence of stabilizing muscle tension, and the ski will receive too much bend in the forebody. This registers to the CNS as instability. Similarly, if the skier flexes and extends their legs, excessive ramp will move that pressure application down the length of the ski in a wave, which, again, creates instability.
The byproduct is a stance that appears to be ‘back of center’, and a ‘set’ degree of leg flexion, which barely changes.
(A good way to tell if a skier is over ramped: If the distance from their ankle to hip socket barely changes while they move from one turn to the other.)
The same postural paradigm is seen in XC skiing, where a skier with too much ramp will ‘sit back’ while descending, while a skier with insufficient heel height will descend pitched forward at the waist, with straight legs. Both will suffer from attenuated ROM, but at opposite ends of the range.
Too much ramp also presents in soft and/or sticky snow, where the athlete notices that the quadriceps group is working harder than normal.
Too much ramp also affects blood circulation to the forefoot, and may account for forefoot pain.
Despite what Jeannie Thoren may tell you, all women do not need heel lifts. In fact, very few skiers ‘need’ heel lifts. (On the other hand, many boot retailers feel a ‘need’ to sell them).
The ramp (Allium Tricoccum) is also a wild edible plant, considered something of a delicacy in the southern United States.
Range of movement at the ankle joint is often used as justification for altering heel height. If a skier has insufficient range, or has an issue with either a hindfoot deformity, or a surgical complication from either birth defect or trauma, heel height/ramp may need to be addressed to ensure that weight is not borne solely (pun intended) on the forefoot. Lacking additional material under the heel, the forward lean of the boot, in combination with the bootboard angle, may conspire to destabilize the second half of a turn on that ski. In this case, increasing the heel height, or affecting the ramp, may be a benefit.
Range of movement, and how that affects flex is a muddier issue. The need for flex is usually related to fore/aft balance issues determined in large part by boot geometry, so once that is resolved, flex becomes less important.
Generally speaking though, most boots have too much ramp for the majority of athletes.
However, this is preferable to insufficient ramp, as skiing with your ‘heel in a hole’ is downright scary.
As with medial/lateral support of the foot, the body is sensitive to minute increments of ramp adjustment. When you get it right, the skier will default to bearing weight along the whole length of the foot, will be able to load/unload the forebody of the ski at will and with very little effort, and will also be able to pressure the ski throughout a turn via flexion and extension of the legs. (And this without large compensatory movements of the torso.)