Originally Posted by MastersRacer
The following comments refer to hard pack/groomer conditions and carving turns (where the edge creates a trough in the snow that it follows from tip to tail).
Small radius skis will make tight turns ala Slalom. Large radius skis will make bigger turns: 21 m - 27 m radius = GS style. DH skis have a radius of 45 m or over.
The length and flex (stiff/soft) of the ski is related to the size of the turn that the ski will make as well. Softer skis are easier to decamber so easier to make tighter turns. Shorter skis are easier to decamber than longer skis of the same radius and will make tighter turns more easily.
Race skis or race stylized skis are torsionally stiff and the tips and tails will grab so the ski will more easily decamber than other skis. Recreational skis have softer torsional characteristics so are more forgiving as they don't bite so much at the tip and tail and won't decamber the ski as quickly. They need greater forces at the middle of the ski to make tighter turns.
Now, to get off the groomers and into the trees or at least not carving.
Radius is less of a function than your ability to get the ski to perform a variety of turns sizes utilizing skidding, not carving. Carving results in speed so is not advantageous in the trees. Speed is ok in the trees, but only with soft snow. Soft snow lets you manage the speed easily by plowing through fresh snow (what I call using snow brakes), pushing the ski into the snow to either cause slowing or decamber and turn.
The shape of the tail is very important in determining how a ski will release a carve and how easily it will permit a skid to develop. Narrower tails release the carve and skid easier than wider tails (width being relative given skis of a particular length and similar turn radii). Turned up tails, like a twin tip, or even the less severe turned up tails that are popular (as on my Rossi B2s) make it easier to release the carve and let the tails skid.
For instance, when I ski the trees, I like my Atomic Powder Plus 165cm. It has a 30+ m radius, but is easy to skid. It is fat (130/110/120). If you went just by radius, you'd think I'm nuts to ski it in the trees, but I don't rely on radius to turn the ski. I can decamber the ski easily in soft snow and because the ski is short it will arc a very small turn. I also smear the tails which is easy because it has a tail that has corners that are rounded and don't catch in the snow easily. My 184cm B2s would work with an 18m radius, but they aren't fat enough to keep me from inadvertantly breaking through the snow. The PP is easier to control. Because it is short and fat, it is easy to pivot, even on softer snow. If I ever get shut down in the trees or get going too fast, I can generally pivot the skis perpendicular to the fall line and do a hockey stop style shut down. It can be tricky with heavier or deeper snow so I usually end up on my side to prevent going over the high side. But I've stopped and usually haven't hit anything.
So short radius
is really only necessary
if you want to make small carved turns
. Short length
skis make pivoted, jumped or skidded turns in the fall line pretty easy.