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Ski stiffness

post #1 of 10
Thread Starter 
Is a car's suspension a fair analogy? Depending on the weight of the person; too soft and you'll pogo; too stiff and the suspension won't absorb the bumps?
post #2 of 10
The relationship between weight (or at least the ability to apply your weight) and stiffness is a factor. Stiffness is a compromise between soft enough to bend when you want to and stiff enough not to when you don't which is why many 'easyturn' skis are also inclined to flap about. I'm not sure about cars.
post #3 of 10
> ...Is a car's suspension a fair analogy?...

If you are thinking of just the springs and shocks, the answer is, "NO". The springs and shocks of a car are not directly involved with helping it turn. For example, if you welded the springs/shocks so that they couldn't move, the car could still turn just fine on a smooth road. (Sidenote - Car enthusuasts, for the moment, lets neglect over/understeer, weight transfer, camber changes, and all that complicated stuff for a second, OK? I don't think that's what he is talking about.)

Yes, the flex of a ski does help you absorb terrain irregularities, but its main function is to help the ski turn. For example, if you made a pair of skis that were infinitely stiff (like the springs/shocks in the above example), they simply wouldn't be able to make a carved turn.

Tom / PM
post #4 of 10
Thread Starter 
I'm not directly talking about turning ability.

Your analysis is fine and dandy on some perfect cord, but I'm talking about cut up, crud, slush, etc.

If you're making gs turns on this, you need to to be able to absorb the bumps. A ski in the air can't turn.
post #5 of 10
I am no expert, but I don't think an overly stiff pair of skis will make you bounce up and down like a pogo stick, e.g. "a ski in the air". Maybe I am not getting your question, shmerham ????
post #6 of 10
Thread Starter 
Stiff skis don't pogo; soft ones do. Stiff ones glide over bumps and inconsistencies rather than absorbing them. This is more efficient, but also offers less control. I don't think it's the main factor in maneuverability, but I do think it makes a difference, but maybe I'm wrong??

Think about skateboards. When they switched from steel to urethane wheels, they were able to roll over small pebbles, and had much greater control. If they went too soft though, they'd be slow.
post #7 of 10
> ...I'm talking about cut up, crud, slush, etc...

Yup. As I said, the flex of a ski certainly does help you absorb terrain irregularities. However, IMHO, that alone doesn't make the analogy to shocks and springs a particularly good one.

The reason is that such an analogy is predictive (ie, useful) only for one part of the behavior of the ski, shock absorption. The analogy blows apart when it comes to another aspect of the behavior of both systems, ie, turning.

Specifically, do the same thing to both systems (eg, stiffen both), and it does one thing to the car (only makes the ride bumpy), but does much more to the skis. It makes the ride bumpy AND makes it impossible to execute one type of turn.

Anyway, we are obviously just chatting about semantics. We both know what happens when you change the flex, so what's the point of the analogy.

Cheers,

Tom / PM
post #8 of 10
Quote:
Originally posted by shmerham:
Stiff skis don't pogo; soft ones do. Stiff ones glide over bumps and inconsistencies rather than absorbing them. This is more efficient, but also offers less control.
As you pointed out in one of your above posts, it is YOU who are doing the absorption. Using a car analogy to model body motion is oversimplification beyond smooth round aerodynamic flying cows.

The bending moment of a ski can be modeled using a spring constant model, yes. There have been threads on this before, notably by PhysicsMan. That doesn't mean it _absorbs_. It means it passes it to your body at a different rate for each 3D 'event'. It is then meaningful only to talk of which ski flex will cause you to make the fewest mistakes in absorption. While doing other things like turning.
Quote:
Think about skateboards. When they switched from steel to urethane wheels, they were able to roll over small pebbles, and had much greater control. If they went too soft though, they'd be slow.
The systems are really incomparable, since you do not actively absorb a pebble with your body.

In the case you speak of soft doesn't necessarily mean slow. Soft AND low-rebound (low return rate) mean slow. Soft and high-rebound mean fast and comfy.
post #9 of 10
Thread Starter 
"Anyway, we are obviously just chatting about semantics. We both know what happens when you change the flex, so what's the point of the analogy."

Yeah. I guess I shouldn't have thrown in the analogy because I was really just trying to confirm whether it was true indeed that a ski can be too stiff if you're going to be encountering inconsistent terrain. ...and trying to see if this is something that one would want to consider; in addition to turning ability (obviously). I wasn't sure if I was experiencing something secondary to the skis stiffness that affected how it handled inconsistencies.

I wasn't really trying to make a one for one analogy. If you want to get down to it; you can dissect any analogy and prove its ineffectiveness.
post #10 of 10
For me at 140 lbs 5'6", where I don't have a lot of weight or height to leverage a ski, the stiffness of a ski can work against me if go too stiff. I do like the solid feel of a stiff ski and like how it allows you to plow through all sorts of irregularities with confidence. But as soon as I get into some tight spots where I need to make quick turns on the fly, I wish I was on a softer easier turning ski.

It's such a fine balancing act when trying to pick the 'right' ski. That's why demos are a must. You just dont know how its all going to come together and work for you till you try it.
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