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Skiing in Powder - Fore/aft balance

post #1 of 131
Thread Starter 
There still seems to be alot of confusion regarding what is ideal fore/aft balance when skiing off-piste conditions. Should I lean back? Forward? What?

I will first try to provide an explanation as to why I believe the confusion exists...and then I will try to provide an explanation to clear it up:

When new instructors are taught to understand and analysis skiing, course leaders try to simplfy things. One key simplification that is made is the snow is assumed to be frictionless. This simplification is valid for beginner to intermediate skiers on beginner to intermediate GROOMED slopes. Since most new instructors teach skiers of this ability on this terrain, this simplification will typically not hinder their abilities to teach.

However as instructors begin to teach more advanced skiers, in more challenging terrain this simplification is no longer valid. The snow does have "friction" or put another way...does resist our movment through it. This is especially true in powder, crud, slush or moguls.

Hence for powder, the deeper snow does exert a force on our feet, in the oppoiste direction of our direction of travel. Thus to stay in balance, we need to recognise this difference and accomadate it.

This is done by having our COM further back relative to our feet then would be the case in say skiing a blue groomer. Thus we are not "sitting back"....we are staying centered....balanced....but to do so does require an adjustment. I typically teach students and other instructors that the best way to move your COM back is to lower your hips...ie more knee bend.

If you do it right, you will not feel any quad burn...if you do get quad burn...you have gone too far back...if you feel yourself getting pitched forward...you have not gone back enough....getting the right amount takes practice and experience and is totally dependent on the conditions....ie, you will need to move your COM back further in 2 feet of West Coast slop to stay "centered" then you would in 3 inches of light dry Colorado Powder...but regardless adjustments are made.

In very challenging conditions, like crud...this adjustment is constant, and can be queit dramatic...this is especially true in conditions where you have icy patches followed by powder patches...you need to anticipate how much friction will be placed on your feet when they hit the powder patch and anticipate.

Hence to answer the question: "Do you want to sit back in powder?" The short answer is "no". You want to stay "balanced"...but to stay balanced, you will need to move COM back relative to your feet.

Hence the goal is to maintain a fore/aft balance....you are in balance when your feet support your COM...(ie, if you took your skis off, you would not fall over)...thus you need to adjust your COM relative to your feet...to keep in balance.
post #2 of 131
Thanks for that account,good job.
post #3 of 131
Volklskier1 - what is you gripe with Skidude's first quoted statement in your post?

Deeper snow (especially snow with high moisture content) does indeed exert more resistance against the skis, bindings, boots and lower leg thereby reducing the rate of acceleration at the feet vs groomed snow conditions.

For this reason the deep-snow skier must maintain a CM / BoS angle that is further 'back' than on groomed terrain as they turn into the fall line and accelerate less than normal.

Not sure I'd suggest his idea of 'lowering the hips' in typical off-piste conditions though. Here, I'd prefer suggest that skiers stay in their typical stance and let the skis surf a lesser angle than the underlying slope (their body stays perpendicular to that lesser ski-angle in the fore/aft plane).

If the skier is actually skiing on *firm* snow hidden underneath a surface layer of unpacked snow then they'd have to make a different adjustment than above - perhaps even flexing more at the knees to 'drop the hips back' as Skidude suggests. Such a position would accommodate the ski-angle under the snow (in the F/A plane) yet keep the skier in F/A balance as modified by the lesser rate of acceleration at the feet.

.ma
post #4 of 131
Quote:
Originally Posted by michaelA View Post
Deeper snow (especially snow with high moisture content) does indeed exert more resistance against the skis, bindings, boots and lower leg thereby reducing the rate of acceleration at the feet vs groomed snow conditions.
Once the skier has hit terminal velocity there is no longer acceleration, whatever the rate. So while the skier might need to anticipate deceleration when entering deper snow by a quick move back, I don't think the skier needs to stay there.
post #5 of 131
Thread Starter 
Quote:
Originally Posted by epic View Post
Once the skier has hit terminal velocity there is no longer acceleration, whatever the rate. So while the skier might need to anticipate deceleration when entering deper snow by a quick move back, I don't think the skier needs to stay there.
This is a common misconception. Gravity is always present. Thus gravity is pulling your COM down the hill....the snow is pushing your feet back up the hill...thus to keep from going over the "handle bars" the feet need to be ahead of the COM. The amount, is a function of slope, snow conditions...and as MichealA pointed out, your ski angle relative to the slope.


Techno Details:

You need to remember what COM represents...it is the point at which gravity acts through the skier. Gravity is always present...hence your COM is being pulled vertically down, the normal force is acting at right angles the slope...the difference is the normally unopposed force which propels you down the hill...again all acting through your COM...however in pow your feet are experiencing resistance. Thus when you redo the vector diagram you will see that COM will need to be further back relative to your BOS to stay in balance.

Perhaps one of the more computer literate can do a vector diagram.
post #6 of 131
Quote:
Originally Posted by michaelA View Post
Volklskier1 - what is you gripe with Skidude's first quoted statement in your post?

Deeper snow (especially snow with high moisture content) does indeed exert more resistance against the skis, bindings, boots and lower leg thereby reducing the rate of acceleration at the feet vs groomed snow conditions.
Snow doesn't DO anything. It is certainly not a force. In addition, I don't stand or turn any differently in powder no matter how deep. If you have trouble in powder it is because your basic technique is bad. Sitting back, toes on top of boots, COM back etc is all hooey.
post #7 of 131
Thread Starter 
Quote:
Originally Posted by volklskier1 View Post
Snow doesn't DO anything. It is certainly not a force. In addition, I don't stand or turn any differently in powder no matter how deep. If you have trouble in powder it is because your basic technique is bad. Sitting back, toes on top of boots, COM back etc is all hooey.


I love this. So Volkl...just a point of clarification...no one is saying snow is a force....but it exerts a force. Dont beleive me? Well ask yourself this then:

If gravity is pulling you down...what keeps your skis from being on the rocks, and dirt. SNOW is exertiing a force keeping you up on top of it....well on the groomers anyway....in pow it holds you up AND back from sliding down the hill.

Still dont beleive me? Ok...so what is quicker...identical run, straightline on groomed or powder? Groomed obviously...why, powder exerts a force on you, which slows you down....

Still dont beleive me? What is easier riding your bike on pavement or in a foot of mud? Again, pavement...no force holding you back...the mud slows you down...just like powder....

And another one....when traversing off piste...do you follow another skiers track...or do you "break trail" on your own....you follow the track....becuase there is less resistanceto your movment...sure snow does not just jump at you with "forces"...it can only act against your motion, hence in the opposite direction to what you are travelling...you know, that idea you already dismissed and gave a thumbs down to:....

This is basic.
post #8 of 131
Quote:
Originally Posted by Skidude72 View Post


I love this. So Volkl...just a point of clarification...no one is saying snow is a force....but it exerts a force. Dont beleive me? Well ask yourself this then:

If gravity is pulling you down...what keeps your skis from being on the rocks, and dirt. SNOW is exertiing a force keeping you up on top of it....well on the groomers anyway....in pow it holds you up AND back from sliding down the hill.
Snow, pavement , mud. They don't exert a force. When a ski or bike tire come into contact with these surfaces it creates friction. Without one moving against the other there is no friction.

Yes, when you are in or on snow it slows you down. Certain types of snow offer more resistance. Why exactly is this a news flash?

The rest of your description of how you ski is just as convoluted.
post #9 of 131
Well said Dude.
post #10 of 131
Quote:
Certain types of snow offer more resistance. Why exactly is this a news flash?
Because if affects your fore-aft balance, and thus the relationship between your BoS and CoM.
post #11 of 131
Quote:
Originally Posted by veeeight View Post
Because if affects your fore-aft balance, and thus the relationship between your BoS and CoM.
How does it efffect your fore aft balance? Go out and straight run in every type of snow and tell me how your fore aft balance was effected by the snow.
post #12 of 131

Question

Is someone saying that skiing a steep slope in deep powder requires a different CoM than the same slope in "packed Powder" conditions" due to snow friction? Perhaps so. I question however

Similarly, Does a Steep powder covered slope require a different CoM placement over the ski, or technique than a less steep slope covered with the same snow? Perhaps, but I don't know certainly.

My own experience suggests that equal slopes require the same mass location, but that skiing "IN' deeper snow provides much more variation in resistance to movement (friction) than firm snow that only offers "surface skiing". (Crud and moguls too)
A high level of CoM accomodation is required due to the action/reaction of the "floating" ski in the supportive snow. The faster I go, the more float produced, the higher I rise out of the soft snow, the less friction from the snow acts on my downhill travels. A self fullfilling proficy.
"Faster and faster, until the Thrill of SPEED overcomes the fear of Death" ;-)

When I make a turn, these dynamic forces are altered.
I slow, and sink, the friction (DRAG realy) increases, I am slowed and also need to make adjustment to remain balanced over my skis. The "movements" required to ski such varied conditions are difficult to "practice" or intellectualize. Hmmm. Skiing is it's best teacher.

One thing I "KNOW". It's more enjoyable to ski balanced over the ski, with tails following the tips, in ALL snow conditions than any other ski method or style.

For me anyway.

A parting thought, using aircraft and flight as analogy.

The forces acting on a moving body (Some seem to move independently I know)

Lift
Thrust
Drag
Gravity

In steady conditions: Lift=Gravity and Thrust=drag
Or else the airplane rises or falls speeds up, or slows down.
Works the same for skiing, just replace the air-plane with snow- plane.

It's All good

CalG
post #13 of 131
So let me get this straight. Spring skiing. Slow sticky snow (but let's assume it's uniformly slow and sticky). I'd have to "lean back" to stay in balance? I don't think so.

If I picture a very, very sticky slope let's say so steep that I can barely move at all and then make it tilt steeply, my COM would have to move back. I don't feel like this happens in practice though. Maybe because the snow doesn't resist "that" much. Maybe it's because the skis tips tend to rise and so you are standing as if the slope is shallower than it actually is.
post #14 of 131
Had to give it some thought and pay attention to what I do in pow, but after my last two runs today I'd say Skidude nailed it. More or less the same for the way I ski bumps.
post #15 of 131
Thread Starter 
Quote:
Originally Posted by epic View Post
So let me get this straight. Spring skiing. Slow sticky snow (but let's assume it's uniformly slow and sticky). I'd have to "lean back" to stay in balance? I don't think so.
.
Correct!

You dont lean back.....you want to stay in balance. This is not to say that adjustments are not made....we will need to position our hips further back RELATIVE to our feet....but that does not mean "lean back"....to me "leaning back" means open the ankle and hip joint...and leeaannnn back...that is not what I am advocating.

Generally speaking, we alter our hip placement predominatley through greater knee flex..ie skiing with the knees more bent then on groomed..

Quote:
Originally Posted by epic View Post
If I picture a very, very sticky slope let's say so steep that I can barely move at all and then make it tilt steeply, my COM would have to move back. I don't feel like this happens in practice though. Maybe because the snow doesn't resist "that" much. Maybe it's because the skis tips tend to rise and so you are standing as if the slope is shallower than it actually is.
Uh...you lost me abit there....but yes as has been pointed out above..in the deep stuff...especially heavy deep stuff with fat skis, the "tip rise" may do most the of the work for you...but that is case by case, and no blanket statment can be made....the key is to simply recognise to ski well we need to be in balance...this means the feet need to support the mass....when we look at all facets of skiing from groomed to deep heavy pow...and everything in between, we need to simply recognise that the variations in the level of resistance our feet encounter need to be compensated for in our stance inorder to maintain balance.
post #16 of 131
Thread Starter 
Quote:
Originally Posted by Max_501 View Post
Had to give it some thought and pay attention to what I do in pow, but after my last two runs today I'd say Skidude nailed it. More or less the same for the way I ski bumps.
Yup...with bumps the resistance comes from the bump "impact"...followed by a lack of resistance as the skis go down the backside...thus constant fore/aft adjustments are required....alot of the adjustments in bumps are "antcipatory"...thus experience is key.
post #17 of 131
Quote:
Originally Posted by volklskier1 View Post
If you have trouble in powder it is because your basic technique is bad. Sitting back, toes on top of boots, COM back etc is all hooey.
I understand what Skidude is saying and it makes a lot of sense from a physics point of view, but I agree with Volklskier. An instructor saying to sit back in powder is just wrong and it's a bad visual to put into a student's head.
Thinking about skiing powder, or east coast chowder for that matter, I am in my same position, and if I come out of that powder and onto a groom run, no adjustment is necessary. vice-versa is also true. If I'm sitting back, it's time to work on my technique.
post #18 of 131
Quote:
Originally Posted by 2-turn View Post
I understand what Skidude is saying and it makes a lot of sense from a physics point of view, but I agree with Volklskier. An instructor saying to sit back in powder is just wrong and it's a bad visual to put into a student's head.
Thinking about skiing powder, or east coast chowder for that matter, I am in my same position, and if I come out of that powder and onto a groom run, no adjustment is necessary. vice-versa is also true. If I'm sitting back, it's time to work on my technique.
its not sitting back though, what skidude is trying to say you COM is back maybe a couple more centimeter.

so say your straightlining a groomer into 2 feet of powder you not going to readjust your COM rearward to counter act the force? you have to be a retard to face plant because your thoughts on skiing dont match what really has to happen, if your that stubborn though you desevre the broken nose.

I am not interested in theories anymore, I do and teach what works if slight change in COM works for the student in powder than so be it.
post #19 of 131
Adjusting your CM to be a few cm farther back is so natural that a lot of folk don't even know they are doing it. To them, they are still "over" their feet. It's just that "over" is derived from a sensory perspective that adjusts for the extra drag. Their cm is continually adjusted to be in line with their feet and the net force acting there.
post #20 of 131
Quote:
Originally Posted by Skidude72 View Post
Yup...with bumps the resistance comes from the bump "impact"...followed by a lack of resistance as the skis go down the backside...thus constant fore/aft adjustments are required....alot of the adjustments in bumps are "antcipatory"...thus experience is key.
I ski steep powder runs much the same as I ski moguls. Good theories here skidude.
post #21 of 131
Quote:
Originally Posted by BushwackerinPA View Post
so say your straightlining a groomer into 2 feet of powder you not going to readjust your COM rearward to counter act the force?
Of course you do, but do you stay back?
post #22 of 131
Quote:
Originally Posted by epic View Post
Of course you do, but do you stay back?
You hadn't better not stay back because sooner or later you're going to have to turn, and that's not going to happen leaning back.

I think that when skiing blues in deep powder, it's pretty hard to even get going without leaning back some. Certainly skiing steeper runs, blacks and chutes, you just jump in and go. I can't ever relate to sitting back while skiing steep slopes in powder conditions, other than going through transition areas and then it's just minor adjustments.
post #23 of 131
Skidude72, you are right. As you bend at your knees two things happen: 1 - it reduces the distance between leg/snow friction and COM and 2 - it moves your COM a little back. Sitting back or leaning back in powder is the mark of a bad skier.
post #24 of 131
Thread Starter 
Quote:
Originally Posted by epic View Post
Of course you do, but do you stay back?
Yes!...and no.


The amount you need to adjust is of course reduced once you pass the transition. Hence lets say you adjusted your COM back an amount "X" to antcipate the slowing....hence you are deliberatly out of balance...as the feet slow, your COM will continue forward...bringing you back into balance.

Now, and I beleive this is your question....once you are in balance...should you stay there? OF COURSE!!!!!!!!!!!!!!!!!!!

Why would you move too far forward and get yourself out of balance?

So the answer is if you move back "X" to antcipate the slowing, after that, once you resume an equilibrium speed you may now be at 1/2X to be in balance...or maybe even 1/8X...just depends....but you will be necessarily in a different position then on the groomed.

Here is another way of thinking about it. If our stance is created manage the forces acting on us such that we are in balance....and if the forces are different in deep powder then on groomed...then how can you possibly maintain a state of balance with different forces...but the exact same body position?

You cant.

Epic,

This a very important concept when looking at higher end skiers in off piste conditions. I am not surprised this confusion exists, as it is the reason I wrote the OP. What I suggest at this stage is...dont take my word for it....discuss it with some others that you perhaps know and respect, like VSP, BB, Mosh,...I have no doubt they will agree with me. The key is to understand that the goal is to ski in balance. This will mean adjusting your COM relative to your BOS...go too far back, and you are "leaning back" or "sitting back", and the usual problems of thigh burn etc will exist...not far back enough and you will be "hanging off the boot cuff", with usual problems, getting pitched over the handle bars, forward pivot point, inablity to carve, down stems etc.
post #25 of 131
Thread Starter 
Quote:
Originally Posted by Ghost View Post
Adjusting your CM to be a few cm farther back is so natural that a lot of folk don't even know they are doing it. To them, they are still "over" their feet. It's just that "over" is derived from a sensory perspective that adjusts for the extra drag. Their cm is continually adjusted to be in line with their feet and the net force acting there.

I think this is an excellant description.
post #26 of 131

Skiing is not a position

It IS dynamic accomodation and balance.

This entire thread confuses.

Place your CoM "back" could as easily be "push" your feet forward.( a thread that has been presented before)

There is no replacement for milage!

CalG
post #27 of 131
This is a pretty easy theory to understand, as is most of this thread if you've been there done that. If you are a good powder skier you already know the technique and mechanics, whether you understand what is being said here or not, whether you think skidude is right or wrong, it's immaterial. Hopefully, you're really good at thinking about what you're doing while trying to do it. Or you're a natural and skiing powder is so easy it's second nature. What i'm trying to say is, there is no substitute for powder experience. You've got to ski it regularly to be good.
post #28 of 131
Thread Starter 
Cgrandy and Lars,

I agree with both of you. My motivations for this thread related more to those who offer advice and MA. I totally agree this idea is simple, and certainly not new...but as this thread clearly has shown it is an idea that is still not fully grasped by some...including some full cert instructors.
post #29 of 131
Does sitting back have anything to do with friction? - Rather than wanting to avoid tip dive because you are in some deep stuff?
post #30 of 131
"The Zone" is a pretty good place to be on a powder day.

To much thinking hurts my head! ;-))

Cal
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