Originally Posted by BigE
It depends. It depends on what you are comparing them to. Skinny straight sticks? yes. Hard snow carvers, maybe not.
The torque on the knee is not just determined by what is going on underfoot, it's also determined by how wide the shovels and tails are AND how torsionally stiff the ski is, and the height of the boot above the lifter.
So Finndog, are the mojo 90's torsionally stiff? Is stiff as say an Atomic SL-11? I doubt it. So the Atomic, with it's extreme torsional rigidity and VERY wide shovel and tail can hurt you alot more, even with just 64 underfoot.
I posted this in another thread recently, but it's also relevant here. The initial torque needed to edge a ski is:
Initial Edging Torque = 0.5*W*w
where w = ski width (perhaps an average) and W = skier weight. This initial edging is a small part of a turn, and you overcome this after about 5-7 deg of edging (the angle of the ski to the ground). If you want to think about the force (not torque) on the knee, then it is:
Initial Edging Force = 0.5*W*w/k
where k is the distance from the knee to the ski base (includes lifters). The shorter the knee, the heavier the skier, or the wider the ski, the more force it takes to edge the skis. Conversely, a light skier with long legs and narrow skis is going to have it easy!
I do consider this to be a "groomed snow" guideline, because this type of skiing minimizes the forces on the knees/bodies down to simple edging inputs needed for carves for the most part. As soon as you get into powder, bumps, crud, etc, there is a lot more going on that will affect the knees, and ski width takes on other roles (such as wider skis making life easier in soft snow, pow, etc). So while I think the equations are good for discussion, there's a whole lot more to it than this. My personal experience indicates that wide skis do take more effort to edge/carve on hard snow, but not a lot -- at least not a bothersome amount. They certainly make life easier for me in any kind of soft snow, so the small tradeoff in hard snow performance is minor.