Why same sidecut for different lengths??

Something I never understood, so maybe someone can enlighten me.
Most skis have the same sidecut for every length of ski.

In general, ski length has to do with weight and height, (aside from skiing style).
So, why should a 160cm ski have the same sidecut as a 190cm ski when they are the same model?? They will ski totally different.
Put another way, short light folks are suffering much shorter turn radius and more extreme sidecuts relative to heavy skiers. Why??

granted, an average rider could chose between a 185 and a 195, be able to flex both, and choose the ski he likes best based on the turn radius. But that same average skier is not going to drop to a 165. And the 120 pound rider is not going to want a 195 ski, so WTF???

Am I missing something here?
I would think that each ski model has a certain feel, and that the manufacturer would want that feel to be the same for all riders, so a shorter ski should have less shape.

you might be confusing sidecut with turn radius.

If the dimensions for a particular model ski are consistent throughout its various lengths, then yes, they have the same sidecut.

However, the different lenghts will produce tighter or longer turn radii.

Unless, of course I'm missing something here ;)

Neither of us is confused, but the reality is confusing.

Here is an example:
Pocket Rocket - all sizes are 122/90/115
165cm 15meter radius
175cm 18 meter radius
185cm 21 meter radius

Rossi Bandit B3 all sizes are 122/94/112
Lengths are 158, 168, 178, 185, 195cm

I could go on, and on, but you get the idea

this could make sense for limited sizes, e.g, Legend Pro Rider, choose 186cm and 29meter radius or 194cm and 32m radius. Most skiers could ski either, and could choose based on radius.
But when comparing a 165 to a 185, or a 158 to a 195, there is no way the same skier will ever want both skis. One is for lightweights, the other is for fatties.

So, why are light folks skiing 15 meter pocket rockets and average to heavy folks skiing 21 meter radius???

As someone on the lighter end of things, I've thought about this some. My take on it is that most mfrs (and consumers?) don't care about a standardized experience. Like it or not, my Work Stinx are going to float me better than they will float a 200-pounder. The "fatter is better" philosophy is very alluring, but given that I weigh half of what some skiers weigh, maybe I don't need those Sanouks? (Hear me rationalizing my lack of superfat skis?)

As far as turn radius/sidecut, they are two different concepts as you recognize -- and yes, given the same width dimensions but different lengths, a lighter skier on a shorter ski will have a relatively "turnier" (and proportionally fatter) ski than a heavier skier on a longer ski. For whom is that a problem -- the lighter or the heavier skier?

Of course, some mfrs do use different width dimensions for the varying lengths of a given model. See, e.g., Black Diamond's ski chart. For example, the Havoc comes in three lengths:

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163 cm | 118-88-110 mm | 20m | Under 155 lb (70 kg)
173 cm | 120-88-113 mm | 21m | 135–163 lb (61–84 kg)
183 cm | 122-88-114 mm | 22.5 | Over 175 lb (79 kg)

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Just buy the biggest, longest ski available and rip shit up.

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Originally Posted by 72Twenty

Just buy the biggest, longest ski available and rip shit up.

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Werd!
https://files.xythos.com/users/amorg...pingItReal.jpg

I might be in way over my head here, but based on my skiing and engineering experience, here are my thoughts:

1. The turning radius the skier experiences is determined by two things, the sidecut and how much the ski is flexed.
2. How much the ski is flexed when turning is again determined by the weight of the skier, snow conditions, speed etc. You can imagine that a heavier (or stronger) skier should be able to push the ski into a tighter turn than a lighter, weaker skier.
3. If a ski otherwise is constructed the same, a short ski is actually stiffer than a long ski.

So if you add all this up you can say that the sidecut is the same, but since the lighter skier on the shorter ski might not be able to flex the ski as much as a heavier skier on the longer ski, the turning radius the skier experiences could be similar.

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Originally Posted by ScottG

So, why are light folks skiing 15 meter pocket rockets and average to heavy folks skiing 21 meter radius???

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Does the turn radius assumption actually work? i.e. are all of the sidecuts circular?

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Originally Posted by runethechamp

I might be in way over my head here, but based on my skiing and engineering experience, here are my thoughts:

1. The turning radius the skier experiences is determined by two things, the sidecut and how much the ski is flexed.
2. How much the ski is flexed when turning is again determined by the weight of the skier, snow conditions, speed etc. You can imagine that a heavier (or stronger) skier should be able to push the ski into a tighter turn than a lighter, weaker skier.
3. If a ski otherwise is constructed the same, a short ski is actually stiffer than a long ski.

So if you add all this up you can say that the sidecut is the same, but since the lighter skier on the shorter ski might not be able to flex the ski as much as a heavier skier on the longer ski, the turning radius the skier experiences could be similar.

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What i thought too...

This theory (that heavy skiers flex the ski more) works for soft snow, but on firm icy stuff, the ski can only flex until it makes complete contact, which should be independent of weight once you have enough force to make contact.

Maybe there is a middle ground, which could explain why BD skis have less sidecut as they get shorter, but they are not all identical radius (their shorter skis have tighter radii, but not as tight as they would be if the sidecut were the same as the long skis).
The BD design theory sounds more logical to me, but few ski mfgrs. seem to do it that way.

Anyone out there in the ski design industry have some real world reasoning and experience??

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Originally Posted by ScottG

Anyone out there have some real world reasoning and experience??

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no, but every year more and more models have adjusted geometries across the line... i think this will be a shift for most manufacterers in years to come. BD's system does seem to make sense, IMO.

one other thing is that while conventional wisdon dicatates that you size the ski according to weight and height, you really are sizing the ski to the customers needs. it only makes sense that a smaller ski should have a shorter turning radius and a longer ski a longer turning radius, because if the customer wants a larger turning radius, then they will need a longer ski so it will be more stable at the greater speed needed to make the larger turn.

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Originally Posted by marshalolson

...it only makes sense that a smaller ski should have a shorter turning radius and a longer ski a longer turning radius, because if the customer wants a larger turning radius, then they will need a longer ski so it will be more stable at the greater speed needed to make the larger turn.

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That makes perfect sense if we're talking about one skier choosing ski/turn radius lengths. But maybe not if we're matching up skis and different size skiers. The BD way of doing things does seem to make sense and illustrates what seems wierd about the regular method.

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Originally Posted by ScottG

This theory (that heavy skiers flex the ski more) works for soft snow, but on firm icy stuff, the ski can only flex until it makes complete contact, which should be independent of weight once you have enough force to make contact.

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I see what you mean, but the point when the ski makes full contact with the snow will also be different depending the angle between the ski and the snow so there's a lot of factors in play here... Maybe that theory wasn't that good anyway. But hey, there aren't that many people carving perfect turns out there either.

Did they ever make the Lawnchair bigger than the 195? Was there a 200?

This is a very valid question. To me, the answer is that if the tip, waist and tail dimensions are the same in every length, then the ski will perform differently in every length. When prototypes are developed, there's always a test length. Rarely are prototypes built in more than one length. Once the prototype is finalized and the design is locked in, then the other length's specs are proportioned off the test length. Each manufacturers has their own formula for proportioning other lengths off the prototype. To further complicate things, think about the flex. If you use the same core shape and sidecut and the same thickness laminates in every size, the skis will get stiffer as they get shorter. Do manufacturers take this into account and proportion things down so that a 165 flexes the same as a 195?
Anyway, right or wrong, for all these reasons and probably some others, skis have always skied differently in different lengths.
PS Atomic varies the dimensions through the size run too.

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Originally Posted by Choucas

...To me, the answer is that if the tip, waist and tail dimensions are the same in every length, then the ski will perform differently in every length...

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Good point.

Related to this, one thing which has really impressed me is my 165 and 190 Explosivs clearly feel like sibling skis, ie, basically similar to each other in spite of the huge difference in length, but very, very different from my g4's, Deep Powders, StormRiders, etc. I think that the reasons for this are that:

a) One doesn't feel so large a difference when going from a high twenty meter sidecut (the 165 Explosivs) to a mid-30 meter sidecut (the 190 Explosivs) as when going from (say) a 11 meter sidecut to a 15 meter sidecut on carving skis.

b) I have the distinct feeling that Volkl does not adjust the thickness (ie, stiffness) of the Explosiv as you go from long to short lengths. This means that the shorter ski will have the same stiffness (inches of deflection per pound applied) as the center section of the longer ski.

Thoughts?

Tom / PM

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Originally Posted by Choucas

Atomic varies the dimensions through the size run too.

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makes sense that the BD's are varied across length then too, since atomic presses the BD skis.

Radius is both a straight line from the center of the circle to the periphery, as well as the circular sweep of that line. You can deduce it on CAD by laying an adjustable circle over the curve in a ski's sidecut until it laps it.

If you increase length without increasing sidecut, the circle gets bigger. Keeping dimensions the same throughout a series of lengths will produce smaller radius turns for smaller skis because the sidecut is deeper, and the circle tighter, as the ski gets shorter.

edit: To answer the initial question: It takes less explaining of a ski's dimensions if you have uniform numbers that fit all sizes. :biggrin:

(pure speculation)

The URL below is helpful to explain sidecut/turning radius and ski length...

http://www.wiredsport.com/02skifacts.htm

James

kind of on topic...say you have 2 skiers of even weight (say 180 lbs), but one is 5'8" and the other is 6'2" how do they flex the ski differently due to their height diff? if they're both on a 185, which (theoretically) should ski a ski with more sidecut? [/gapic question]

Wow. This thread was started a year ago this Friday.