Is Ski Weight Really that important?

[popof]

There is another way to look at this issue (or to try to understand it):

 

If you guys have ever heard car manufacturers, they are always trying to lower what they call "unsprung weight" on vehicles. Unsprung weight (http://en.wikipedia.org/wiki/Unsprung_mass) is all the weight (or mass if you want) that is directly connected to the pavement, and not supported by suspension. Therefore suffering directly from road bumps etc..

 

Please forgive my approximative English, but if you try an "analogy" (?) you could say that the ski and the binding on a skier are the Unsprung Mass (maybe even his lower legs, up to the knee), and the rest (above the knee) is the Sprung mass (given that your knee is your highly-evolved suspension device ;) ).

 

And from there on, please read the Wikipedia article stated above,

 

(specially parts like

High unsprung weight also exacerbates wheel control issues under hard acceleration or braking.

)

 

and you'll see many reasons why a lighter ski / binding (and lower leg, but that's not something we can adjust haha) are better for your skiin'

 

Hope people will understand what I tried to say here, and hope it helps.

[SkiJay]

I totally get what you are saying @popof. I think comparing the unsprung weight of a car's suspension to "from the knees down on a skier" is a valid analogy, and there's an interesting difference between the two when it comes to stability.

 

In a car's suspension, lighter is more stable because it improves how well the suspension can react to and comply with solid media, the bumps and dips in asphalt. In water skiing, the bumps and dips are not solid, and more mass is more stable.

 

The question remains, is a stable high-mass ski better or worse than a nimble low-mass ski. My vote goes to lighter being better. Anytime you have to accelerate, decelerate and corner with something, lighter is faster ... until the point where it gets too unstable or unreliable. In addition, the suspension on a skier is "active" suspension. It can anticipate and adjust for most significant bumps, like the wakes and rollers, and in active suspension, lighter is always better.

[RazorRoss3]

I haven't used enough skis to know what the effect of ski weight is but I've found that I ski better when I personally weigh less

 

[BraceMaker]

@popof - one exception I would probably make here, sprung mass ie. a wheel is reacting primarily vertically from the ground.

 

Your car is turning, your wheel is bouncing, your goal is to keep the rubber of the wheel planted such that you can corner, and the reaction of the tire bouncing off the ground must be absorbed, reduced, and the tire returned to the ground.

 

This to me is very similar to the ski, when the ski is closer to under the skier. That being the more upright the skier-leg-knee-hip the more similar it seems to the unsprung weight concept.

 

But how does this change through the various stages of the slalom skiers stance?

 

Essentially we have a skier - 200 lbs, we have two ski packages of identical configuration, that is same stiffness, width, length, bindings. Package A has a ski that weighs 3 pounds and 5 pound of boots, package B is 5 pounds of ski, 5 pounds of boots.

 

From hook up through the wakes we have a ski that is on edge (same skier so same form/edge changes etc). While on edge, we have his weight + ski weight + dynamic weight (pull from boat) transferred against the water by a ski that is on edge. Skier encounters a water imperfection midway from ball to 1st wake.

 

Regardless of ski weight we have quite a bit of "load" in the system, and the system is reacting against this water imperfection through a diminished ski surface area (edge). Combined with this we have a relatively rigid suspension on our system, as the skier has the legs and core engaged to combat the pull from the boat. Does this skier have the same concept of unsprung weight? Does 2 pounds of ski matter much against the weight + hundreds of pounds of load?

 

Same skier punches through the wakes and begins the edge change, now his body weight is not on the same lean against the line, his load is diminished, the ski is flatter as it switches edges, and the skier lacks the load for his core to be engaged on, so the suspension system is less rigid, more supple. In this stage a water imperfection is acting almost vertically through the flatter running surface of the ski, through vertically oriented legs, against the skier who is not adding the load of the tow line through his legs on the system. Now we can check that same 2 pounds? Probably meaningful?

[DW]

I agree that the analogy is very useful and valid, but something to think about. A tire does not care how it's vertical load is applied to allow it to generate the force for cornering. Stripping away all the inertial effects of simple ballast weight, a tire does not care if the load comes from aerodynamics or simply weight, it responds to that load the same way. It does however affect other elements like momentum and acceleration.

[eleeski]

That 2 pounds is at the end of a long lever arm. It will move the center of mass (COM) of the skier by an amount you can feel. 2 pounds added to the COM (usually near you gut) will have less effect than the same 2 pounds at the end of the ski.

 

Race cars use lightweight wheels downstream of the suspension. They keep everything light.

 

Regarding rebound, most skis are stiff enough that the magnitude of flexing is small enough that rebound and dampening are insignificant. In skis, flex doesn't matter, stiffness matters. Disclaimer: it is possible to design a ski that has a lot of flex and have it work well - I can't do it though. Personally, the stiffer the better.

 

Ask for a reride if there is an imperfection in the water.

 

Eric

[ForrestGump]

Last week I switched from Exo hardshell bindings to a Reflex front and rear toe plate. Yeah, I know...... might as well have switched feet at the same time. lol. Net result was 3 1/2 lbs less ski weight. The edge change is a LOT quicker. I'm sure part of that is because the heel is free now. BUT, the ski feels livelier as it moves out now which has to be weight based.