|Originally posted by Lew Black:
One factor that has not been addressed is fore/aft stability. ... I don't know that PM's torque analogy is applicable when making anything close to a carved turn. Even when you hit a hard lump of snow, if your momentum is mostly forward the extra length will stablize when the lump slows you down. Hopefully you going over the lump, not skidding sideways into it...
Hey Lew - Thanks for your comments.
You are absolutely right that I didn't discuss fore-aft stability. The reason is that I was trying to address what I saw as the main concern of the guy who started this thread, "...Will a longer ski be more difficult to turn and more difficult to turn quickly?.."
. Accordingly, I just focused on rotary/yaw issues, even those seen when a ski is going sideways, because, lots of people are in situations and are at skill levels where they can't carve every turn in whatever type of soft snow they are dealing with and will usually have at least some sideways slip in their turns (particularly, when they get nervous in crud).
You are also absolutely correct that a longer ski will have more fore-aft stability, especially when carving.
In fact, I'll be the first to admit that the longer ski will even have more yaw stability (carving or not) in the sense that the average amplitude of the random yaw motions (say, in a skarved turn over a cut-up surface, and assuming the skier is applying no rotary input to correct these) will be less. OTOH, while it sounds really counter-intuitive, the force (torque, actually) exerted on the skier's boot for given sized angular (yaw) perturbation will actually be larger for the longer ski. (But in fairness, these larger angular excursions will be less frequent on the longer ski.)
The converse of this is that the skier will have to work harder (ie, apply more torque) to get the longer ski to come back to the direction it should be pointed.
It's basically the skiing / rotary version of difference between a responsive sports car vs a stable sedan. You feel every road irregularity more in the sports car, but the sports car allows you more control over its path.
One final note, while going long at a fixed width will certainly smooth out some of the fore-aft perturbations caused by snow of irregular density, so will going wider at the same length.
The extra width will allow your skis to consistently stay high in the lighter, top layers of the snow and not be constantly going up and down into every irregularity.
IMHO, some effects are a wash between going fatter and going longer. For example, the mass of the skis increases with both width and length, and extra mass smooths out the constant speeding up and slowing down encountered in rough snow. Extra mass also allows your skis to better displace clumps that are in your way.
Similarly, I think its also more or less of a wash between fat and long with respect to the benefits of having decreased average pounds per square inch of loading on irregular snow in terms of compression of the irregularities.
The one mechanism by which longer beats out fatter is that with a longer ski, the tip displaces or compresses snow irregularities, and the rest of the ski (assuming in a carved turn), can simply follow in the previously smoothed path. You don't get the same benefit by going fat instead of long.
Anyway, definitely an interesting discussion. Gotta run.
Tom / PM
PS - Comprex: Good stuff, but no time to respond. I've got to prepare for a trip. I'll be back next Fri.