Let's talk turn radius (short vs long)

[HateBoilerplate]

I've been watching the product landscape for the ski industry for a couple years, trying to gauge what skis to demo, and demoing as many as I can (with what little selection the pro shops at the little hills in Michigan tend to have), and I find myself curious about one thing in particular:

Is the shorter radius just what people have come to like, or is there a technical reason that most advanced/expert skis tend towards a shorter radius (<17m) for carving skis (and even most(?) all mountain skis)? The skis I've liked skiing on the most are around 21m (estimated based on a radius calculating website - they didn't list radius as a spec when the K2 Merlin V was made) - and I've always kind of gravitated towards GS skis (my pair before the K2s was an old pair of French VR17s), but I don't see that sort of radius commonly on the spec sheets, other than on GS race skis (or powder skis, but I live in Michigan, so...yeah.)

Is it possible to carve a significantly longer turn on a shorter radius ski without sliding it? Every ski I've put on edge at speed that has a shorter radius, as decided it was time to end the turn far sooner than I would've preferred (essentially forcing a slalom cadence, rather than letting me carve big, open curves all over the hill). If there's a different technique I can try, I'd love to hear about it.

 

[James]

One can do pretty huge turns on a slalom ski. 36 feet (<12m) is a pretty big circle. Flex characteristic have a huge influence on how things ski.
We used to use the little carving skis, roughly 110cm, to make big turns.

 

[BGreen]

I think the change in radius is due to a few things. First, slopes are more crowded than ever before and ski areas are cracking down on anything they deem fast skiing, which really is anything faster than a low level intermediate would go. If you look like you have the potential to ski fast, that is enough to lose your ticket. For that reason, more advanced skiers are trying to get further from the beaten path.

On the technical side there are a couple reasons, but both are chicken/egg discussions. People are carving more complete turns because the skis can do it and people are making tighter turns because the skis have tighter sidecuts. This means bumps are different shapes and in different places from when VR17s ruled the slopes.

You also need to understand how modern skis work with regard to flex, side cut, and rocker, and how that translates into what you like. For example, for me, a softer 27m ski is more versatile than a stiffer, narrower 21m ski. I have two powder/all-mountain skis (same brand, year, model) in a 185 and 193. If you got on them you would have trouble believing they are the same brand let alone same ski. I’ve also come to understand that skis are somewhat location specific. What works well for me at my home mountain is not necessarily what I would choose when I ski anywhere else. Still, it’s hard a beat a low 20s radius GS.

 

[François Pugh]

First of all recall that in order to hold a turn, you have to tip the ski up to a critical angle (that angle depends on how fast you are going and how tight the turn is).
Second, when you tip your ski up to that angle on a hard surface, the actual radius your ski will scribe on the snow is much smaller than the "side cut" radius written on the ski. Tip that ski up to 60 degrees and your looking at half that radius.

Two main reasons I can see for the popularity of smaller radius skis are that you can make more turns going down smaller hills, and if you were arcing longer radius turns (like half of 70 m on your antique speed skis), you would be going mach schnell, and most folks don't want to ski that fast.

You are also correct that if you want to carve a large radius turn smoothly you need a large radius ski. The better small radius skis will do it, but the quality of the turn won't be as smooth.

Also note that most folk do not carve arc-2-arc, neither on modern skis, nor did they on their old skis. The extra shape of the smaller radius skis nevertheless helps them make smaller turns, even though the turns are not carved arc-2-arc.

 

[James]

Turn radius has actually gone up, not down, in the last several years. When Kastle came out with skis in the 20m range for a mid 170's ski I thought they'd be horrible. They weren't.
But flex pattern and overall stiffness is very important. I can force a short turn out of the 22m/192cm Stormriders because of a soft tip.

If the comparison is to skis with 60-70m radius and ridiculously stiff, there is none. The only thing the old ones were better at is going straight. Maybe ballet if they're short enough and had turned up tail.

 

[Philpug]

Don't get hung up in the numbers, check out The Numbers Game; Skis. Realize there are many ways to measure a turn radius to make the numbers fit into the marketing hierarchy of a segment. I would just assume manufacturers simplify things and just go so "short", sub 15M, "medium", 15-20M and "large", over 20M. Past that it is hyperbole in most cases.

 

[James]

Well, we need numbers. But we need understanding more.
Hart tried to say for awhile the sidecut was too complicated to post. They just looked like morons.

Then there's Black Crows which is measuring length to 0.1cm. Now that's just stupid. Did someone from hart go to work there?

 

[Tony S]

Edit: Others were faster than I was on some of this.

Is it possible to carve a significantly longer turn on a shorter radius ski without sliding it

Yes. But it's not hard to find longer radius skis if that's what you want, notwithstanding the pendulum of trends.

Every ski I've put on edge at speed that has a shorter radius, as decided it was time to end the turn far sooner than I would've preferred

Can we name names and lengths? Do you have video? If you're trying to go by "book knowledge," that's good, but not sufficient. This is especially true if your reference points are from 20 years ago, as sounds possible. You need to demo.

If I were skiing groomers in Michigan I'd be on a slalom-esque ski for my everyday pair. Why? Because I like to ski arc to arc on firm snow. Compared with brushed instructor turns or a bump run, that requires some space, even on SLs. Much more on a GS ski. I'd be wanting to maximize turns on a small and possibly busy hill. Totally personal preference.

Anyway, if you haven't been trying newer skis, you should before putting money down.

 

[flbufl]

Actually, Black Crow is doing what Philpug suggested, categorize turning radii to short, medium, long, etc.

I think the reason why Black Crows measures numbers to the 10th decimal is that they design each model of their skis to be length specific. You can see from the numbers below, different lengths of the same model, Camox, have the same waist width and turning radius, but slightly different tip and tail widths.

Well, we need numbers. But we need understanding more.
Hart tried to say for awhile the sidecut was too complicated to post. They just looked like morons.

Then there's Black Crows which is measuring length to 0.1cm. Now that's just stupid. Did someone from hart go to work there?

 

[flbufl]

The traditional way (which is still be used by almost all ski manufacturers) to calculate the turning radius does not take the ski flex into account.

Vist create the concept of "dynamic radius", which I think is much more realistic and practical.

http://www.vist.it/en/technology-and-materials/skis/

DYNAMIC RADIUS
The “dynamic radius” concept indicates the ski’s capability of closing a turn through the movements of the skier and was conceived to overcome the low reliability of the turn radius usually indicated. The turn radius is a geometrical measurement given by the width of the tip, centre and tail that provides a specific result based on their distance. This trigonometric calculation does not keep into consideration other ski characteristics, like flexibility, as described in the DIN ISO 5902 standard.
Taking into account ski deflection and typical parameters of the turn radius, it is possible to obtain the data related to the closing of the ski as it is pressed onto the snow, with values which are much closer to the real ones. Vist indicates the “dynamic radius” on its skis to facilitate the skier in selecting the most suitable product for his or her own needs.

I've been watching the product landscape for the ski industry for a couple years, trying to gauge what skis to demo, and demoing as many as I can (with what little selection the pro shops at the little hills in Michigan tend to have), and I find myself curious about one thing in particular:

Is the shorter radius just what people have come to like, or is there a technical reason that most advanced/expert skis tend towards a shorter radius (<17m) for carving skis (and even most(?) all mountain skis)? The skis I've liked skiing on the most are around 21m (estimated based on a radius calculating website - they didn't list radius as a spec when the K2 Merlin V was made) - and I've always kind of gravitated towards GS skis (my pair before the K2s was an old pair of French VR17s), but I don't see that sort of radius commonly on the spec sheets, other than on GS race skis (or powder skis, but I live in Michigan, so...yeah.)

Is it possible to carve a significantly longer turn on a shorter radius ski without sliding it? Every ski I've put on edge at speed that has a shorter radius, as decided it was time to end the turn far sooner than I would've preferred (essentially forcing a slalom cadence, rather than letting me carve big, open curves all over the hill). If there's a different technique I can try, I'd love to hear about it.

 

[James]

I think the reason why Black Crows measures numbers to the 10th decimal is that they design each model of their skis to be length specific. You can see from the numbers below, different lengths of the same model, Camox, have the same waist width and turning radius, but slightly different tip and tail widths.

Keeping the sidecut the same for different lengths is just a design decision that's not new. Describing length to 1/10th centimeter is new and a marketing decision. We're talking about it. There's no basis at all to be that precise. How is length even measured? That doesn't seem to be standard.

 

[flbufl]

Let me try again to explain myself better this time For side cut, it is sometime necessary to be precise to the 10th decimal of millimeter to reflect the length specific design. I guess they did the same for the ski length in centimeter just for having the same format.

Keeping the sidecut the same for different lengths is just a design decision that's not new. Describing length to 1/10th centimeter is new and a marketing decision. We're talking about it. There's no basis at all to be that precise. How is length even measured? That doesn't seem to be standard.

 

[James]

Let me try again to explain myself better this time For side cut, it is sometime necessary to be precise to the 10th decimal of millimeter to reflect the length specific design. I guess they did the same for the ski length in centimeter just for having the same format.

No, it's not. There's "This is what it says on the computer" and common sense. For god's sake call it a 175cm ski. Not 174.6. I seriously doubt the manufacturing tolerances are within 1mm for length. Flash is usually cut with a bandsaw by hand. Then rough ground by hand. So, it makes even less sense.
Alpine skiing is timed to 1/10,000 of a second at the Olympics. (At least at Sochi where there was a tie) They only report to 1/100 of a second.

Meanwhile, back to the "we're not hung up on numbers" thread. Excepting just about everyone, esp Black Crows.

 

[Philpug]

Again this is not new. When Salomon came out with their skis, in the 9000, there was a 1S, 2S and 3S, in the same distance, the 1S made one turn, the 2S, two turns...and guess how many the 3S made?

 

[graham418]

So... how do manufacturers come up with the radius number? Is it a purely theoretical number based on tip- waist tail differential? Is it for a fully loaded and flexed ski ? On edge? Or something else? Is it just a relative number like boot flex?

 

[Philpug]

So... how do manufacturers come up with the radius number? Is it a purely theoretical number based on tip- waist tail differential? Is it for a fully loaded and flexed ski ? On edge? Or something else? Is it just a relative number like boot flex?

Dependng on who you talk to, it could be "yes" to any of the above.

 

[François Pugh]

For their racing skis, they use a specified calculation. See page 43
http://www.fis-ski.com/mm/Document/...tionequipment_1617_11072016_clean_English.pdf

 

[James]

It wasn't till shaped skis that people knew the sidecuts. And then a ways in. Atomic had their 9 34, 10 26 etc. where the second number was the radius afaik. 9 was slalom, 10 GS.

Old test reviews of straight skis often? put radius in their test page stats, but it wasn't printed on the ski. Early shapes were not radius but sidecut difference in mm. From the tip? Not sure.

 

[François Pugh]

Here's an interesting article. https://www.skiinghistory.org/history/evolution-ski-shape

 

[Tom K.]

Mostly, because it's easier to adjust a short radius ski to a longer turn than vice versa.