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# How does turning radius affect performance?

Take three skis. One has a turning radius of 13m, the next 16m, the next 20m.

All things "being equal", how different will they perform on groomers, in crud, in bump and in powder, etc?

When do you want the shorter? When do you want the longer radius?
Obviously the shorter radius skis work best on shorter turns and the longer ones best on longer turns. I use shorter radius skis for lower speeds, and longer radius skis are for higher speeds.

On a small hill where I cannot reach high speeds, I take the short radius skis, otherwise I would make two turns down the hill. I make more turns and get more turns per dollar spent.

The short radius skis will not carve a turn longer than their sidecut radius on hardpack. If I want to make longer turns I will be on longer radius skis. If you are going fast there won't be enough traction available to make a short turn anyway, so you may as well use the long radius ski. Remember the force required to turn you is M(V^2)/r where V is speed, r is the radius and M is mass.

Short radius skis are not safe for high speeds, imho.

Don't forget that the turn radius the hill sees is the side cut radius multiplied by the cosine of the tipping angle, but past a certain point the ski won't bend any more and breaks loose.
Your skis turn because of the sidecut radius and longitudinal flexing. If you just look at one you are not getting the complete picture. A ski with not much sidecut but soft flexing can be pushed to carve a smaller radius turn, whereas a ski with a lot of skicut will have to be let go from a true carve to make a large radius turn. I think the stiffness of the skis' tail does more to dictate the radius of your turns than the sidecut in most situations.

I like "straigher" skis without much skicut. They are more stable and less squirrley in the powder and crud. I am sure others will disagree, but for me a 13m ski works going slow, but when I pick up speed and start making bigger turns I feel that I am skiing past the sidecut. Tight radius skis were fine in Wisconsin where they have long lift lines and short runs, so I wanted to make as many turns as possible, but once I moved out west with softer snow and more wide open terrain I gravitated to straighter skis with a softer flex.

I think the bottom line is that if you like to make big turns and carve them, then with a 13m ski a big a part of many of your turns need to be skidded a little in order to achieve the desired bigger radius. Matching the sidecut to your skiing style is just a matter of demoing the ski and seeing through how much of your average turn it will hold a carve. The unltimate is to have both a pair of turny hotrods and some gs cruisers.
there are 2 additional very important aspects that have not been mentioned!

#1) torsional stiffness, how much the ski resists twisting whn the ksi is set on edge. A lot of torsional stiffness makes a ski hold better on very hard snow. so actually a shorter ski with a lot of side cut may carve longer turns without skidding better then a torsionly soft longer ski.

#2) Actual shape of the sidecut. It is just mot the side cut radius itself that disctates turn shize abd shape. but taper angle! Taper angle is the width of the tail dimension compared to the waist of the ski. High taper angle allows a much more versatile turn shape, where low taper angle (wider tail) creat more across the hill finish to the turn and tends to lock a ski into a more specific turn shape, (read less versatile turn shape)

Stifness of the tail of the ski although an aspect that goes into all of this, is not the main contributing factor nor does it dictate radius of your turn more then then the sidecut radius and taper angle.

Tail stifness if more about fore/aft balance. tail stiffness is more about a kick or accelration at the end of the turn creating the need to recenter fore/aft.
In deep snow the "turning radius" depends more on flex than side cut shape, but the same applies. Short radius (soft longitudinal flex) skis for slower speeds making more short turns, long radius (stiffer) skis for making longer higher speed turns, but there is a limit. Super stiff skis, especially stiff tails don't work all that well in deep powder on mild slopes. All skis should be torsionally stiff, imho.
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 Originally Posted by Ghost In deep snow the "turning radius" depends more on flex than side cut shape, but the same applies. Short radius (soft longitudinal flex) skis for slower speeds making more short turns, long radius (stiffer) skis for making longer higher speed turns. All skis should be torsionally stiff, imho.
I sold my Kastle 208 Sg's years ago. Then I ran into the guy i sold them to & was going to buy them back. He said he would just give them to me. But never hooked up with him again. They had Geze bindings on them and were absolute planks!
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Where is the defining radius for "short"? begin?
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 Originally Posted by Ghost In deep snow the "turning radius" depends more on flex than side cut shape, but the same applies. Short radius (soft longitudinal flex) skis for slower speeds making more short turns, long radius (stiffer) skis for making longer higher speed turns, but there is a limit. Super stiff skis, especially stiff tails don't work all that well in deep powder on mild slopes. All skis should be torsionally stiff, imho.
I agree except I think the flex is more about (obviuosly along with width) dive or float and fore/aft balance. Radius and shape is more about turning even in deep snow.
Quote:
 Originally Posted by Atomicman I sold my Kastle 208 Sg's years ago. then i ran into the guy i osld them to & was going to buy them back> He said he would just give them to me. But never hooked up with him again. They had Geze bindings on them and were absolute planks!
They are pretty dead until you get over about 55 mph. After that the faster you go the better they feel.
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 Originally Posted by Ghost They are pretty dead until you get over about 55 mph. After that the faster you go the better they feel.
No question about faster = better!
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 Originally Posted by Atomicman Where is the defining radius for "short"? begin?
Good question.
The short radius is relative to the speed you wish to go. A 20 m turn is a short turn at DH speeds, but a long turn at SL speeds. A 1.5 g turn at 13m is about 30 mph, and about 43 mph for a 24m turn.

Since language is interpreted by the typical user, I'll say short radius is under 14 m, and long radius is over 24 m, but I may be biased.
Hey Ghost,
Where di you get your knowledge of physics?
I'm overeducated. Why do you ask? Did I make a mistake in the metric conversion? No I don't work for NASA.
NO mistakes, I was just impressed!

### Pardon my rant!

"Stifness of the tail of the ski although an aspect that goes into all of this, is not the main contributing factor nor does it dictate radius of your turn more then then the sidecut radius and taper angle.

Tail stiffness is more about fore/aft balance. tail stiffness is more about a kick or acceleration at the end of the turn creating the need to recenter fore/aft." Atomicman

My personal experience seems to dispute this. If you complete your turn on a ski with a soft tail you will continue to carve around in a smooth arc. On long very soft tailed skis I can rear back at the end of the turn and actually tighten the arc by punching the flex of the tails. To me a stiff tail ski robs you of the last 1/3 of your turn by interrupting the arc by pushing you straight. You say it simply accelerates the skier at "the end of the turn," but to me it in fact prematurely ends the turn whether you want to or not and therefore lengthens the arc. I think soft tails allow you to tailer the arc of your turn to a much greater extent, in any kind of snow condition.

I grew up when the only high performance skis were racing skis, which all accelerated you out of the turn, and in my opinion way too many skis still suffer from that design. I generally turn to slow down, why would I want a ski that accelerates me out of every turn? If I hear a ski has "snap", "pop" or is "lively," I generally avoid them. Give me an old Atomic "dead sled" or a Volant any day. I realize my personal preference is not the norm.

I appologize for my rather strong come on, but you can probably tell that this has been a crusade of mine for most of my ski career. It comes down to personal style. Stiff tails are fine if you want to attack the mountain, but I guarantee you that you will run out of legs before your run out of mountain for the day. I can take my soft tails, work them into the trough of a mogal or a crud or powder turn, and use the flex of the ski to do the work of both turning and slowing me down, and the sidecut of the ski has almost nothing to do with it. So at least for me, I think that tail stiffness is the main contributing factor to the radius of the turn. Bad skiers spend too much time with their weight on their tails, but many good skiers don't spend enough time there because their choice of equipment punishes them for it.
Quote:
 Originally Posted by Ghost Good question. The short radius is relative to the speed you wish to go. A 20 m turn is a short turn at DH speeds, but a long turn at SL speeds. A 1.5 g turn at 13m is about 30 mph, and about 43 mph for a 24m turn. Since language is interpreted by the typical user, I'll say short radius is under 14 m, and long radius is over 24 m, but I may be biased.
I like it! I would agree

How did FIS come up with the different radii X, where X > or = to r for different events?
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I never said stiff tails was a good thing or that I liked a ski with a stiff tail. I also have never equated the words, pop, snap or lively with the tail of the ski.

From the description of your skiing , we are going to have to agree to disagree. you are merely manipulating your fore/aft balance to weight different parts of the ski to accomplish the end result.

I am talking about the natural unmanipulated (skiing centered) natural turn shape. So you can see why the shape of the tail is so important. A larger tail forces you to finish across the hll more (this is just an undeniable reality)

I pay more attention to where and what my skis are doing from the center forward. the tails just follow! I am more interested in how the tip and forebody reacts in a trough, crud or powder.

Skiing from the tails seems counterproductive IMHO.
The only reason to be on your tails is to accelerate out of a turn. (Racers do this all the time).

So I would agree we have very different styles of skiingI I let the sidecut and edge angle do the work! I am almost never on my tails and if I am I normally recenter ASAP!

Good skiers stay off their tails because if you on your tails you are out of balance and can't use the natural shape of the ski to turn and carve clean turns.

Sorry but IMHO Volants were the most boring, dead old man's ski I have ever skied on, & it had nothing to do with the tail!
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 Originally Posted by Atomicman Skiing from the tails seems counterproductive IMHO. The only reason to be on your tails is to accelerate out of a turn. So I would agree we have very different styles of skiingI I let the sidecut and edge angle do the work! I am almost never on my tails and if I am I normally recenter ASAP! Good skiers stay off their tails because if you on your tails you are out of balance and can't use the natural shape of the ski to turn and carve clean turns.!
I guess I was not very clear, I do not ski from my tails, I start the turn on my tips just like you, I just rock my weight farther back through the turn in an attempt to try and use the entire length of the ski to continue the turn. I am not out of balance, I am simply striving to move my balance father back along the length of the ski. My complaint is that if you do this with a stiff tailed ski your turn is short circuted by an acceleration as opposed to finishing carving on the continuing arc (i.e. a smoother finish to the turn).

You said, "I am almost never on my tails and if I am I normally recenter ASAP!." The point I was trying to make was that your skis may not give you any choice because at that point you have lost your carve when your skis accelerated out from under you. With a softer back end I can maintain balance farther back on my skis giving me more options. I look at it as having a longer window of choice as to when I end the turn, and an extended time period to continue to shape it.

Obviously we have different styles which require different skis, but I would not generalize to the point of saying that "good skiers stay off their tails." I think we should use the entire ski to expand the variety of turns we have at our disposal. Some skis are designed to be skied farther back. I am sure you are an excellent skier and I am not going to presume to tell you what kind of equipment to use or how to ski, but I feel that if I cannot stay balanced on the back half of my skis then I don't think the ski is providing everything it can for me. Acceleration from leaning back is a given, I just strive to minimize it through softer tails. My feeling is that I paid for the whole ski and damn it I'm going to us it.
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 Originally Posted by mudfoot I guess I was not very clear, I do not ski from my tails, I start the turn on my tips just like you, I just rock my weight farther back through the turn in an attempt to try and use the entire length of the ski to continue the turn. I am not out of balance, I am simply striving to move my balance father back along the length of the ski. My complaint is that if you do this with a stiff tailed ski your turn is short circuted by an acceleration as opposed to finishing carving on the continuing arc (i.e. a smoother finish to the turn). You said, "I am almost never on my tails and if I am I normally recenter ASAP!." The point I was trying to make was that your skis may not give you any choice because at that point you have lost your carve when your skis accelerated out from under you. With a softer back end I can maintain balance farther back on my skis giving me more options. I look at it as having a longer window of choice as to when I end the turn, and an extended time period to continue to shape it. Obviously we have different styles which require different skis, but I would not generalize to the point of saying that "good skiers stay off their tails." I think we should use the entire ski to expand the variety of turns we have at our disposal. Some skis are designed to be skied farther back. I am sure you are an excellent skier and I am not going to presume to tell you what kind of equipment to use or how to ski, but I feel that if I cannot stay balanced on the back half of my skis then I don't think the ski is providing everything it can for me. Acceleration from leaning back is a given, I just strive to minimize it through softer tails. My feeling is that I paid for the whole ski and damn it I'm going to us it.
Ok, i can accept that. I have no need to ski on my tails. No circumstance when i really feel the need to be back there. but we are back to what dictates turn shape flex or shape!

Specifically tail flex. And I still say it is shape more then flex.
Umm....

Thanks for the "input".

After post #3 I got lost. I already knew that long radius skis did longer turns better and short radius skis were better for tight turns. It was good to see that if I want to go fast, short radius skis are not the choice. But can you go fast on a 13m Metron? Can you do tight turns on a 17m B3?

Side note-resort report: Skied Dodge today, despite the marginal snow the groomers were great! Two runs did have a few rocks tho. Most were rock free.
Quote:
Originally Posted by SNPete
Umm....

Thanks for the "input".

After post #3 I got lost. I already knew that long radius skis did longer turns better and short radius skis were better for tight turns. It was good to see that if I want to go fast, short radius skis are not the choice.
Quote:
 But can you go fast on a 13m Metron? Can you do tight turns on a 17m B3?
Side note-resort report: Skied Dodge today, despite the marginal snow the groomers were great! Two runs did have a few rocks tho. Most were rock free.
Yes you can
Quote:
 Originally Posted by SNPete Umm.... Thanks for the "input". After post #3 I got lost. I already knew that long radius skis did longer turns better and short radius skis were better for tight turns. It was good to see that if I want to go fast, short radius skis are not the choice. But can you go fast on a 13m Metron? Can you do tight turns on a 17m B3? Side note-resort report: Skied Dodge today, despite the marginal snow the groomers were great! Two runs did have a few rocks tho. Most were rock free.
But can you go fast on a 13m Metron? Yes but it wont feel as stable as the B3 especially in crud and powder.

Can you do tight turns on a 17m B3? yes but the turns will require more input from you and will be less dynamic. In powder and crud though short turns will become much easier to do. The B3 is pretty soft and will bend quite fast with a platform to go against.

IMO straighter skis rule in soft snow, on groomers it depends on the size of turns then choose raduis by that.
OK so we're back to the "some skis are better for somethings vs others". I've come to the conclusion (after demos etc) there are always compromises and you just have to build your quiver for each situation (given infinite spendable cash that is
Sure, you can ski a 13-m side-cut radius ski at 60 mph, but you will be taking a bigger risk with it than you would with a 30-m radius ski. Jamming the tip wrong or catching a buried bump or anything else going wrong will produce near-instant calamity.

Trying to carve a 26 m turn with a 13-m ski on hardpack won't work too will though. You will have to have a sideways component of your motion to make the 26-m turn radius, because even flat your edge going straight ahead will only "carve" 13 m. It won't feel as good.

There are techniques that will let you carve a tighter turn with the longer radius stiffer ski. They require big edge angles, and perhaps putting all your weight on the tips followed by moving the weight to the tails pressuring the apex of your turn as it were while the skis go through it. I think you won't be able to make a very long sustained short radius turn however. For more extreme turns you can use only the outside ski to help you bend it. You can also scarve tighter turns, or else you can just skid the tails around.

The above has to do with the interaction of the side-cut with the surface of the snow.

For 3-D skiing consider the ski in the turn being an upside-down beam with support in the middle (your leg) and a uniformly distributed load (the snow on the bearing surface). You can see that side-cut determines how much load is on each part of the ski. How stiff the ski is determines how much deflection the beam will have with a given load. The flex and side-cut work together to shape the ski. It really is more complicated, with forward momentum possibly loading the tip more or less depending on your actions, but this simple model gives you a little understanding.
SNPete: Sorry about highjacking your thread. The sidecut vs. soft flex issue kinda hits a never with me, but it looks like these guys have answered your questions.

A good skier can make either ski work anywhere, it basically comes down to where do you want to scarve the most. Good skiers tend to go with the longer radius sidecut ski because it excels at what they do the most, which is ski fast and make bigger turns.
Thanks for the info guys. I am kinda new to the sport and am hungry for information. Being new, the shorter radius skis are what I need at this point, but I do want to work on speed also. Now if any of you need mtn biking advice or tips..........

Interestingly my wife, who is an advanced level skier, just got some 11.5m skis ('07 Soloman Siam 8). On those skis, she skis faster than she did with her '04 K2 T-nine Spires, which had a 16m radius. Just goes to show that it is the skier more than the skis
What would you guys say would be the optimum compromise turn radius for different turn shapes? Would Skicross skis have that compromise with their 15-19m turn radius that seems to sit between SL and GS skis?

Am considering demoing a Salomon Crossmax V12 in 178 cm length (16.2 m turn radius) which for my height (182 cm) and weight (200 lbs) should be a good compromise between short turns, long turns, edge grip and ability to go fast.
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 Originally Posted by Dr. Will What would you guys say would be the optimum compromise turn radius for different turn shapes? Would Skicross skis have that compromise with their 15-19m turn radius that seems to sit between SL and GS skis? Am considering demoing a Salomon Crossmax V12 in 178 cm length (16.2 m turn radius) which for my height (182 cm) and weight (200 lbs) should be a good compromise between short turns, long turns, edge grip and ability to go fast.
also look at Atomix Sx models and Head Supershape Speed. both more durable then Salomon's and much more solid fell 9espescially the Head)

Both very quiet and fast.

Beside being an exceptional performing ski, The Head has extremely high quality construction and real side walls and a very durable topskin and burly tip protector.

also pay attention to tail dimension compared to waist and tip. Narrower tail compared to waist = more versatile turn shape.
Quote:
 Originally Posted by Atomicman also look at Atomix Sx models and Head Supershape Speed. both more durable then Salomon's and much more solid fell 9espescially the Head) Both very quiet and fast. Beside being an exceptional performing ski, The Head has extremely high quality construction and real side walls and a very durable topskin and burly tip protector. also pay attention to tail dimension compared to waist and tip. Narrower tail compared to waist = more versatile turn shape.
Thanks for the info. Have already tried the Atomic SX12 supercross in 174 cm, didn't like it too much because it was a bit too much like riding an express train on rails in that I was comimitted to carving large turns. When I wanted to ski outside the rails and do different things such as short turns it didn't grip as well.

Haven't checked out the Head yet though. Tried the Equipe GC race which is apparently almost an identical ski to the Crossmax (in 170 cm though which is why I need to demo the 178) and the base seemed to hold up well to a few bare patches. The advantage of getting the Crossmax also is that you can get it for under 450 euros in Andorra!
It depends on how fast you ski.

Since centripetal acceleration is V^2/R, if you want to make say a 1-g turn while banking, 'cause your lazy, with your skis tipped to 45 degrees, then V=sqrt(9.81m/s^2 * (sin(45 degrees))*16.2m) or 10.4 m/s or about 24 mph.
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