This is a concept I only noticed recently in some smaller brands. Mostly I wonder which approach actually produces a more consistent ski across lengths for skiers of different weight or speed preference. On paper I would think that fixed radius scales down for weight better, but perhaps changing any dimensions, including length, almost always changes the character of the ski, so other considerations are more important. I also wonder whether part of it is a marketing issue - it is easier to market a ski as one ski across its lengths if its other dimensions are consistent?
Fixed width vs. fixed radius design philosophy - any thoughts?
quite the contrary. Several of the largest companies have different lay ups for each length of their top of the line skis, resulting in flex characteristics that are stiffer in longer lengths than shorter lengths. The TR is listed for each length and usually varies, longer skis with longer TRs. Varying the waist width is not so common, or not published at any rate, but I think I have detected very slight variations in width through the lengths on some models I have owned, generally owning one of the two shortest models, 165 or 175. I believe the idea is that the ski perform the same for skiers of different strength and weight.
Girth? I know, width, but not a common term in the shops I frequent.