Skier weight and ski stability

[KingGrump]

Stein didn't ski with his skis under his shoulders. He was a power skier.

Stein is definitely a power skier. In fact he can be any type of skier he wants to be. He is a beautiful & functional skier. One of my idols.
It's the skiers that tries to ski like Stein that miss the mark. They emulate the style without understanding the actual functional portion of Stein's skiing. Sad.

I see something very similar on Outer Limit at Killington every weekend. Bunch of young skier would ski the bumps there with their legs glued together. Emulating the form of a comp bumpers. They are usually good for about 10 bump then they are exhausted. Huffing and puffing. Just standing there wit their burning quads. EMulated form without the understanding the function that lies beneath the form.

I spent the past season skiing daily with a bunch of instructors at Taos. The skiing of couple of them is what I have in mind when I think of power vs finesse. Let's call them Mike and Pete. Mike is ex-racer. Usually on a pair of race skis. Trenches the groomers, run gates and pounds the bumps with them I swear the bumps are a little bit smaller after he has gone through them. Pete on the the hand, skis like silk flows down the hill like water. One of the things that is often said about Pete is "Is he slipping or carving. Doesn't matter, he looks the same."

To me, Mike is the definition of power skier while Pete is a finesse skier. Both are really good skiers. Both are PSIA examiners. They just get things done differently.

Jackson's definitions of power skier vs finesse skier are more like my definition of a skier that can work their skis and a wannabe. To put it bluntly, his finesse skier sucks while my finesse skier can kick ass with the best of them.Often you just don't realize when or how.

I can understand why Jackson basically calling a good chunk of his readership - finesse skier. Hey, it is all about eye ball count. I do not share the same constraint.

 

[François Pugh]

That realskiers definition of power versus finesse skier has always irked me. It's best to be taken in context and serves a limited purpose when dealing with realskiers reviews and descriptions. I see no reason why power cannot be applied with precision and finesse.

As to instability, back in the day when skis had a side-cut radius between 30 and 80 m things were simpler. Skis became unstable at speed when they started vibrating so badly that they could not grip the snow/ice beneath them. Sure the old Dynastar chicken heart SLs were advertised as being stable, but that was relative; take them up to DH speeds and they were vibrating like spit on a wood stove.

Now it's a little more complicated. With short side-cut radius skis (say less than 13 m), the skis also interact with every undulation in the snow causing them to hunt for turns right and left if held flat. That is a separate issue than the old familiar excessive vibration. You can deal with it by alternating setting one edge then the other, up until about 45 mph and after that you can just tolerate it. They'll still want to turn willy-nilly, but so long as you don't dig them in, you can just ignore it (with a little nerve). My old (but still shapely) 165 cm Fischer WC SCs will hunt for turns, but they won't get the DTs, even when pushed way past their design envelope. At 60 mph they (the SCs) are still more stable than my old 190 cm Volant Machete Gs. Take the Volant Machetes above 50 mph and the tips and tails just want to dance the wango-tango; I'm afraid to make hard turns on them at speed that are easy peasy on the my antique SGs.

Back in the day, longer was more stable, certainly for race skis. For example my old Kastle SGs at 208 cm were more stable than the 205 cm length, but not as stable as the 213 cm length (I know because I tested all three lengths). For lesser skis, e.g. some Atomic recreational skis I've tried, it seems at least sometimes the longer skis are no more stable; they just have more mass farther out there at the tips vibrating out of control.

Thanks for all the replies. It's reassuring to see I'm not alone in my experience interpretation.

 

[BGreen]

@François Pugh I’m going to disagree with based on my ability to vary my weight run to run moving equipment around. In my experience, a ski can perform to its expected capabilities up to a skier of X weight, and starts having problems once that weight is exceeded. In your example, let’s say your skis can handle 190 lb. They would be fine whether you were 140 or of 180. If you weighed 250 or 300, they would feel uncomfortable. I think this is mostly an issue of overloading the tips (when you rest on the fronts of your boots, you are still pressuring the tip).

So if I have a pair of skis built for load that surpasses my weight, all is well. However, if I’m on a pair of skis built for my weight (in this case a pair of 165 slaloms built probably for a U16), and then ski down the hill carrying 50+ lb., they get scary fast.

 

[François Pugh]

Oh, I have a good grasp on that aspect of it, and I concur with what you say @BGreen . I know when a ski is overloaded, but that's not what I mean when I say unstable. A ski is overloaded when it is asked to exert more force than it is capable of. A 250 lb skier making a turn will overload a ski when a 150 lb skier won't overload that same ski making that exact same turn with that ski. It can be scary pushing a ski to the point of overloading it when you have to rely on being able to turn. A 180 lb skier trying to make a 3G turn will also overload a ski that behaves fine when making a 1 g turn.

However, when straight-lining a steep line a 180 lb skier won't feel any more unstable than a 140 lb skier straight lining that same steep line in those same conditions on that same ski.

Edit: It's probably no coincidence that skis that are hard to overload are also less likely to be unstable at speed. They are built to a higher standard of stiffness and energy absorption/dissipation.

 

[Tony S]

Anyone else?

Yeah, BS you're slow. I've skied with you

My tongue was in my cheek. Someone knocked a chip off my shoulder and I was grumbling aloud.

 

[BGreen]

@François Pugh I’m talking about straight line. Bases were flat, base edge bevel 0.5.

A ski doesn’t experience much force when flat because it is supported underneath (why you need a high edge angle to bend a ski), but they can still deflect from snow input. Now I admit this is somewhat theoretical because my experience is limited to different flexes of a single brand of 165 slaloms, but I would think that would hold true with longer skis, but speeds would be much higher. The issue is a flat ski is supported fully when skier weight is least (w*1g) and least supported when skier weight is highest (w*3g). FWIW these particular skis are soft enough in the tips that I can feel the tip twist off when loaded.

The point of my previous post was that even the softest skis of a reasonable length can handle the loads required to go straight, but if you have a particularly weak pair of skis and you can change your weight significantly between runs (a couple bundles of gates is probably 50 lb., salt bags are 40 lb., full dye pack is probably 60 lb.) that is already straining under your mass, it’s easier to notice the difference. As a point of reference, my sister at 110 lb-ish likes them but also finds them a bit weak.

As always, just one person’s opinion from a single data point. Hardly Gospel.

 

[François Pugh]

@BGreen I'm imagining a situation with fairly hard snow with say about six inch bumps. A heavier skier with enough weight to compress the ski to the bottom of the troughs and bending the tips and tails at the peaks up to a certain speed, where a light skier at that speed would be bridging those troughs and not bending the peaks and tails as much, skimming along. In that case the heavier skier, bending the ski more at each bump would put more energy into the ski, perhaps exceeding the skis ability to dissipate that energy? Where as the lighter skier, putting less energy into the ski at each bump would need to ski faster to overcome the ski's ability to dissipate the energy (more bumps per second instead of more energy per bump). It's condition dependent: in the conditions described above ski has a lower speed limit for the heavier skier, but for conditions where the ski is equally displaced (smaller bumps harder snow) the ski has the same speed limit. Does that match your experience?

 

[skix]

Although F may equal MA I think that equation alone is too simple to describe differences between lighter and heavier skiers. One complicating factor must surely be the ratio of mass to ski surface area. While a skier weighing 100 pounds has less M than a skier weighing 200 pounds don't we also need to consider how much surface area that force is spread across while the ski is flat and how much edge is in the snow while carving? If a 100 pound skier distributes their mass over a ski with half the surface area of the 200 pound skier would not the force per unit area be equal to the larger skier? The ratio of weight to edge may also play a role.

Of course we're also assuming the relationships are linear with increasing weight and that there's no step effect where, for example, the snow acts one way up to a critical mass per unit area but then acts differently when that ratio is exceeded. ... Point being, as a small guy, I hate to see simplistic equations cause every small skier to be encouraged away from competing in downhill because of "physics". No way things are that simple and I suspect this dogma has been accepted without much actual science besides thought experiments.

Going down the rat hole of common-sense, and with no idea if it is correct, I can construct a rule to explain why smaller skiers are more nimble than larger skiers. Nerve length from brain to foot is significantly longer in tall individuals. When a big skier decides to move their foot then at the fixed speed of a nerve impulse it takes longer for their decision to be acted upon than for someone with shorter nerves. Therefore big skiers are more clumsy than small skiers.

 

[BGreen]

@François Pugh Honestly I haven't thought that much about it. I just don't take those skis if I'm skiing with gear in soft snow.

 

[Tony S]

This forum would experience much lower overhead if some wonderful midnight cowboy would sneak into Ghost's house at night and just burn all his gear that's more than 15 years old, replacing it with five year old stuff from a ski swap. I'll pitch in.

 

[KingGrump]

This forum would experience much lower overhead if some wonderful midnight cowboy would sneak into Ghost's house at night and just burn all his gear that's more than 15 years old, replacing it with five year old stuff from a ski swap. I'll pitch in.

You are having a good day, aren't you?

I know a few guys here that would volunteer in a heart beat.

 

[dbostedo]

This forum would experience much lower overhead if some wonderful midnight cowboy would sneak into Ghost's house at night and just burn all his gear that's more than 15 years old, replacing it with five year old stuff from a ski swap. I'll pitch in.

Ghost's? Who's that?

 

[Marker]

Francois is Ghost?

No disrespect, just didn't realize.

 

[Tony S]

I'm presuming. Sorry for the shorthand. Seemed suitable in the moment. Apologies all around.

 

[Blue Streak]

I know I have at least 30 different screwdrivers in my toolbox, ranging from the largest breaker bar to the smallest eyeglass screwdriver.
I don’t wonder whether I have a power tool box or a finesse toolbox.
It’s just a complete tool box.
If only my skiing were so.

 

[markojp]

I'm presuming. Sorry for the shorthand. Seemed suitable in the moment. Apologies all around.

No, you're correct.

 

[Tony S]

No, you're correct.

As I've been told many, MANY times in my life, being right doesn't mean you don't need to apologize.

 

[François Pugh]

I'm presuming. Sorry for the shorthand. Seemed suitable in the moment. Apologies all around.

Confirmed. No worries.

 

[KingGrump]

As I've been told many, MANY times in my life, being right doesn't mean you don't need to apologize.

You married too?

 

[Andy Mink]

It should be interesting this year to see/feel the difference between skiing last year at 225# and this year at 221#. Hoping for around 200# come the season.