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Math Question

post #1 of 14
Thread Starter 
Being relatively new to the sport, I am trying to gain an understanding of various aspects of skis. Length, width and how it all translates into how a ski performs.

I understand that stiffness and other aspects of how a ski is made play a major role in a ski's performance. For this thread I am seeking opinions based on “all other factors being equal” so I can focus on this one aspect.

So my question is this. Compared to my old 107-68-97 K2s which were 160s, my new 157cm Metron 9s have about 10% more surface area. So with all other factors being equal, it would appear that a ski with the dimensions of the Metron would behave/ski like a 175cm, 107-68-97 K2.

How accurate is my assumption?
post #2 of 14
Could you please confirm the dimensions of both pairs of skis please? It seems one of the K2s is longer than the other K2, and there is no tip-waist-tail given for the Metron 9.
Edit: I just realized your old k2s were 160 and your wondering if the new metrons would ski like a new k2 that was 175 cm. Could you give me the dimensions of the metron 9, and perhaps the model of k2. I would say no.

You might want to check out Physicsman's sidecut radius calculator.
post #3 of 14
Thread Starter 
Quote:
Originally Posted by Ghost
Could you please confirm the dimensions of both pairs of skis please? It seems one of the K2s is longer than the other K2, and there is no tip-waist-tail given for the Metron 9.
My Metron 9 is: 124-74-108.

BTW, the second, longer K2 is hypothetical. I am assuming that both K2s have the same tip, waist, tail dememsions for the sake of this example.
post #4 of 14
Those two skis won't be that similar, even ignoring differences that arise from construction, flex, etc.

The Metron has a sidecut radius in the 12 meter range, and at 84 mm is fairly wide underfoot.

The 175 K2 has a radius in the 17-18 meter range, and is middle-ish (by today's standards) underfoot, at 74 mm.

There is a faulty assumption in the notion that the primary way to evaluate general dimensions is in terms of surface area. Two skis with the same surface area may be entirely different. To take a rather obvious example: your Metrons vs. a 215 cm GS ski from 1992 (I think they'd both be in the same ballpark in terms of surface area).

Personally, if I were trying just to look at dimensions and reduce it to the bare minimum, I'd look at not fewer than three numbers: sidecut radius, length and width underfoot.
post #5 of 14
imho:
The narrow longer k2 would be quicker edge to edge, not as forgiving at slow to medium speeds, but nicer going faster. More susceptible to terrain imperfections doing pivoted or skidded turns. A force has more effect when it is farther away from the centre of the ski.

The wider shorter metron would be more forgiving at slow to medium speeds, easier to balance in soft deep snow and more of a challenge at speed.

The smaller turn radius of the metron will also be noticeable.
post #6 of 14
Thread Starter 
Thanks.

So the underfoot size is a biggie? And I didn't think about the radius.

And from what ghost is saying regardless of surface area a longer ski would be better at speed. I kind of suspected that. So are you are saying there is dynamic and the 157 Metron is not equvilant to the 175 K2, except in weight bearing? If so, then a person should decide what performance factors are more important to their skiing goals when choosing between a short fat or a long and not so fat ski. (assuming one can only own one ski, which seems to be the case with 80% of skiers)

A quick aside, how fast is "at speed"? I ask this, because so far I go as fast as my brain will allow and I notice the Metrons do fine. Of course I am not that fast of a skier, yet.
post #7 of 14
You have to be very careful and qualify your statements here. A longer ski provided it is stiff enough and has proper damping characteristics and is not excessively skinny (min. say 65 mm, 68 is better) is better at speed. A longer noodle would be a nightmare.

Yes you have to define your priorities: width underfoot based on snow depth and hardness, turn radius based on the turns you like to make and the turns you don't want to compromise on, length and construction based on weight and speed.

Also consider flex balance on intent.
post #8 of 14
Thread Starter 
Quote:
Originally Posted by Ghost
You have to be very careful and qualify your statements here. A longer ski provided it is stiff enough and has proper damping characteristics and is not excessively skinny (min. say 65 mm, 68 is better) is better at speed. A longer noodle would be a nightmare.

Yes you have to define your priorities: width underfoot based on snow depth and hardness, turn radius based on the turns you like to make and the turns you don't want to compromise on, length and construction based on weight and speed.

Also consider flex balance on intent.
This is very helpful. So many factors. Nothing is simple. I am glad I am not presently in the market for new skis. I could see myself getting headache if I were trying to decide on new skis.

I got lucky in that the Metron fits what I want in a ski at this point in my skiing career. Right now my growth focus is going down steep ungroomed blacks with success. I will let speed come, as it may, in due time.
post #9 of 14
Quote:
Originally Posted by sjjohnston
Those two skis won't be that similar, even ignoring differences that arise from construction, flex, etc.

The Metron has a sidecut radius in the 12 meter range, and at 84 mm is fairly wide underfoot.

The 175 K2 has a radius in the 17-18 meter range, and is middle-ish (by today's standards) underfoot, at 74 mm.

There is a faulty assumption in the notion that the primary way to evaluate general dimensions is in terms of surface area. Two skis with the same surface area may be entirely different. To take a rather obvious example: your Metrons vs. a 215 cm GS ski from 1992 (I think they'd both be in the same ballpark in terms of surface area).

Personally, if I were trying just to look at dimensions and reduce it to the bare minimum, I'd look at not fewer than three numbers: sidecut radius, length and width underfoot.
SJ, The M9 is 74mm underfoot
post #10 of 14
Thread Starter 
Quote:
Originally Posted by Atomicman
SJ, The M9 is 74mm underfoot
Yes and the K2 in question is 68 mm underfoot.
post #11 of 14
Quote:
Originally Posted by SNPete
Yes and the K2 in question is 68 mm underfoot.
I didn't want to hammer him that hard, he probably knew it, but ran out of edit time!
post #12 of 14
Thread Starter 
Quote:
Originally Posted by Atomicman
I didn't want to hammer him that hard, he probably knew it, but ran out of edit time!
Yes he was kind enough to respond to my question. I would not have mentioned the error. But since you pointed it out, I felt it was OK to correct him on the K2 ski.

So what is your take on my "math question"?
post #13 of 14
I think SJ was right on, waist width is a big factor, but an additional factor that has not been mentioned is taper angle.

That is how much narrower the tail is then the tip.

the narrower the tail the more versatile a turn shape a ski will usually have because the tail does not "lock" into the arc at the end of the turn. Skis with more equal tip or closer to equal tip & tail dimensions want to make 1 turn shape.

Another factor is torsional stiffness, how much the ski resists twisting.

so now you have Longitudinal Flex and flex pattern (not just how stiff or flexible the ski is but where it is stiff or flexible)Torsional rigidity, sidecut radius and side cut shape (taper angle) waist width, length, and overall surface area.

In addition threre are differences in construction & materials (core, wood, foam, laminate, torsion box, cap sidewalls) and design.

Add to all this the skis profile for example thicker or thinner and where. Vibration dampeners, and power channels and beta lobes

All these things make a ski ski differently.


But I think in a more general way your basic assumption (very generally speaking) is correct in that the shorter fatter ski, skis longer then you would expect it to.

But I don't think you can say it skis like another particular ski in a particular length without skiing on that ski and comparing the performance of the two.
post #14 of 14
Quote:
Originally Posted by Atomicman
I think SJ was right on, waist width is a big factor, but an additional factor that has not been mentioned is taper angle.

That is how much narrower the tail is then the tip.

the narrower the tail the more versatile a turn shape a ski will usually have because the tail does not "lock" into the arc at the end of the turn. Skis with more equal tip or closer to equal tip & tail dimensions want to make 1 turn shape.
One of these years I'll get to that project. :
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