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How fat is too fat?!!!

post #1 of 6
Thread Starter 
So I was looking at the new Volkl Sumo that is out for the '05/06 season. It has a ridiculously fat 145-125-142 sidecut. I imagine this will be sort of like using water skis on snow. So what is a reasonable top end for the width of snow skis? Have we hit finally hit the end with the Sumo?
post #2 of 6
I found myself asking the same question when flexing the new Line Prophets. I was in sheer awe of the ridiculous dimensions of these skis (130 at the waist). Is this a novelty thing? Or will they actually prove to be practical east of, say, Alaska?
post #3 of 6
Thread Starter 
I remember someone mentioning that there was a thread where Physicsman described how ski dimensions translate into the amount of float they provide (can't seem to find it). I'd be interested in knowing how much float (how many pounds they can support) the Sumos have at a given speed. That would answer my question of why the manufacturers are going even wider. Can anyone help out?
post #4 of 6
http://forums.epicski.com/showthread.php?t=2275&highlight=float+width+surfac e+area

Physics, Man:

Then, there are at least three separate factors that people always tend to lump together when they are comparing the "float" of different skis in powder:

1) The average depth of the flexed ski under the surface of the snow;

2) The depth to which the skier (or at least his boots) is immersed in the pow; and,

3) The tendency of the ski to nose dive and auger in to bottomless powder.

You asked whether a lighter skier on the same skis will experience worse flotation due to their inability to flex their skis.

What will happen is that for your hypothetical lighter skier, #1 will be less, #2 will also be less, but #3 will be more. So, for some light people, the most noticible thing about a particular ski (in bottomless powder) may be its propensity for un-nerving tip-diving, so they will simply report that this ski "doesn't float well", even if most of the time, it was only a few inches under the surface because of their light weight.

Basically, the apparent paradox which you found only arose because of the vagueness (multiple-meanings) in the commonly used term "float".

I could go on for pages about what design parameters influences each of the above three observables, but I think the most important points for deep powder (ie, not in stratified or partially compacted conditions) are:

1) A flat ski tends to dive for exactly the same reason that a flattened hand held out of a car window at 60 mph tends to get pushed down if it is at all tipped downward. Ball up your hand (ie, let the ski flex a bit) and this effect goes away. If a stiff ski is always tip-up, it will give you lots of support in bottomless conditions, but make even a little fore-aft error in such conditions, and you will go over the handlebars.

2) The average depth of the flexed ski under the surface of the snow (#1, above) is determined pretty accurately by the total load bearing area. A simple and surprisingly accurate formulat to calculate this is just A = Length * average_width, where average_width = 0.25*tip_width + 0.5*mid_width + 0.25*tail_width.

3) The depth to which the skier feels immersed in powder (#2, above) is not the same as the average depth of immersion of the ski because in bottomless conditions on soft skis, due to the flex of the skis, your boots may be many inches below the average depth of your ski. With stiff skis (relative to the skier's weight), there will be almost no difference between #1 and #2, but with soft skis, the middle of the ski can easily be 6 inches further immersed than the tip (even if the ski is level), and this will contribute to an overall feeling of being more "in the powder" or "less float" for a soft ski of the same surface area as a stiff ski.


Tom / PM
post #5 of 6
Why becuse they sell. It's a bigger is better thing. if 80 is good 90 is better if 90 works why not 100 and if..... well you see the results with the Line Prophets and now the Sumo. Now the question is do they work? Sure in bottmeless powder but really how many days do we get that in a season? Even at Powder Meccas like Alta you don't get those conditions everyday. As a quiver ski if you live in or near a real powder area sure why not? As an everyday ski no way.
post #6 of 6

(How wide are your hips?)+ 5mm = (too fat)

as ryan already posted the content equivalent to:

Physicsman's equivalent float chart:

and the 'careful about the other variables including ski length!' caveat lector,

I start to wonder when offset-to-the-inside binding mounting will come back to haunt us.
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