Ski design points and concepts

vinman · Post by **vinman** » Mon Feb 17, 2014 6:29 pm

We don't a have a lot of discussion here on the various types of ski design concepts.

I want start a thread on the various design concepts and now to manipulate them into a workable ski design.

Concepts like tip shape, taper, pin tail, rocker, camber, various sidecuts and radius...how to combine these to come up with a purposeful design.

One of the first things I want to talk about first is tip design on reverse sidecut-rockered tip sections. I really like a shark nose/bullet shaped tip for pow/crust/mank but they can feel twitchy on hard snow and some folks feel like even in soft conditions they can feel this way. Much of this can be changed with proper tuning ....but that is another topic all together.

Have any of you experimented with striaght sections in this kind of tip? So something like a shark nose tip with a flatter sidecut section at the wide point that transitions into traditional sidecut? I'm think that this would feel less hooky/twitchy but still give the feeling of cutting though cut up snow well, which the shark nose/ reverse sidecut tip does well. This might also perform better on harder snow than a full reverse sidecut tip...???

Please discuss and share ideas, this is now that aspect of building skis that intrigues me the most these days.

sammer · Post by **sammer** » Tue Feb 18, 2014 12:51 am

Funny you should bring this up vin...
I was out today, 20+cms of heavy, very tracked up snow, on a pair I built a few years ago.
The Ballistas, basically a pair of reverse/reverse that I put a 22m sidecut in.

My thinking today was they'd be ok, should be able to cut thru the crud.
They were OK as long as I was charging hard, (no quarter) but once I switched to a more traditional side cut ski ( portly) I felt a little more at ease.

I'm not sure if the sidecut I put in this pair was just not in the right place, but all the theory says they should have been the right ski for today.
I got worked over pretty good by these skis today, very early taper just felt wrong.
The portly's traditional side cut definitely seemed to work/feel better.
Both have the same slight but full rocker/ flat camber.

I know this is very subjective but I'm not sold on early taper, full reverse/reverse in the right conditions is awesome but, I seem to feel way more confidant on a full traditional sidecut ski...
Today's conditions favored full rocker/ flat camber, normal sidecut, worked awesome.

As I said if you could keep on them (no quarter) the balistas were pretty good. But even then they worked you over.
Don't really know how else you could describe it!
The pic of the balistas above makes it look like the side cut is way back but it's more centered. Might have to re-investigate this at a later date!

sam

vinman · Post by **vinman** » Tue Feb 18, 2014 4:25 am

Sam, I'm thinking more of a reverse sidecut tip with rocker, combined with traditional sidecut and camber thru the rest of the ski.

I've built this design quite a bit, I love this design but I think it could be better if I decreased the amount of reverse sidecut. I've been using about 5-6mm of reverse sidecut. This is measured from widest part of the rocker to a point at 150mm from the tip.

I'm thinking that making this flatter, 2-4mm taper, might keep the best of this design in powder/corn/mankind/crust but decrease the hooky feel on hard snow.

sammer · Post by **sammer** » Tue Feb 18, 2014 9:14 am

I think I hear what your saying, the widest part of the ballistas is about between the EE's in the word treefrog and it's quite a lot.
They're about 125mm 150mm back from the tip and 135mm just between the ee's (about 420mm back from the tip). It's all a bit too much.
If I was to pursue the tapered tip idea in the future, I'd make it a lot less drastic.

sam

twizzstyle · Post by **twizzstyle** » Tue Feb 18, 2014 1:54 pm

I started experimenting with a similar shape last year. The powder skis I did last year have been awesome - great in powder (155mm at the tip), but the short sidecut section (only about 100cm long, on a 160cm long ski) makes them great on groomers and everything in between. I don't have a good side shot, but they have pretty big rocker tips, and LOTS of camber in the middle.

The skis I made last fall have a similar shape, just overall much narrower. I've only had them up once so far and they were good, but slightly hooky. I may be able to alleviate that by de-tuning the edge a bit where the normal sidecut transitions to reverse sidecut. Must just have to do with the relative placement of that transition relative to the start of the rocker tips.

vinman · Post by **vinman** » Tue Feb 18, 2014 3:13 pm

Yeah twizz, I think thiat design is inherently hooky if not beveled an detuned properly.

twizzstyle · Post by **twizzstyle** » Tue Feb 18, 2014 3:56 pm

Is that sort of the shape you were driving at? It can be so hard to describe these shapes.

I wonder then if moving the sidecut transition forward of the rocker transition would help some of that?

vinman · Post by **vinman** » Tue Feb 18, 2014 4:31 pm

Twizz, that shape is close. To decrease the hooky feel I put a 2 degree bevel on the base edge of the rockers and detune aggressively. This will make that tip shape behave and the ski will carve as it should. The higher bevel also makes it so you can throw it sideways to dump speed in deep snow without catching a tip.

vinman · Post by **vinman** » Wed Feb 19, 2014 6:13 pm

Twizz, so in effect you'd have the rocker extend beyond the widest part of the ski?

I guess this would make the ski behave more like a traditionally cambered ski with a rocker tip....???

The shape I'm thinking of is more along the lines of the armada tst.
http://armadaskis.com/product/skis/sign ... eries/tst/

This places the fattest part of the ski at the rocker base and is also the front point of contact. This is how I've been designing my ski but with more reverse sidecut in the tip. But this design has me thinking....

Y · Post by Y » Thu Feb 20, 2014 6:13 am

really interesting topic !
twizz, can you share more numbers about your skis
I plan do build same sort of skis for my wife, about the same size (158)
I wonder what radius you used, and are you happy with it ? I plan to set a quite short radius, around 14/15m, to have a ski that turns easily and quicly around trees

PS : I'm a snowboarder, and have build only snowboard so far, so I have a lot to learn about ski shapes

falls · Post by **falls** » Fri Feb 21, 2014 3:56 am

I think a small amount of tip taper is good. Low rocker so you can extend the sidecut up into the rockered tip but when you make a turn (especially on hardpack) you can still engage the sidecut. This design seems to work in powder and hard pack pretty well.
Like the line mr pollard opus.
http://m.youtube.com/watch?v=c2_3Na68HYc

I have made a more armada Jj shape tip tapered ski which I liked a lot in powder but less so in chopped up or heavier snow. In powder the narrow tip rises really well. Ok on hardpack but didn't really like the 16m radius and short running length if you were spending a lot of time on the groomers.

petemorgan(pmoskico) · Thu Mar 27, 2014 11:23 am

I like a tight smaller radius for quicker giant slalom carving turns, and the ability for super quick turns in tights spots. they wont feel that stable at high speeds, but for accelerating in and out of a carve, i just love a tight radius. how small of a radius have you guys gone?

I am curious how the sidecut radius interacts with the camber. I am always using rocker tip, sometime more, sometimes less.

I find that the rocker tip actually creates a bit of its own "radius" in a turn. especially when float skiing. I think the rocker tip also acts as its own radius on the hardpack when leaned over far enough.

I am 5' 6" and this year i have been skiing almost exclusively on a pair of skis with tight radius probably close to 13 or 14 meters, and only about 88mm underfoot. loving them! I taper the radius at the tip, and think that i could maybe even have tapered it more and would still hold onto the tight radius that i desire.

I just finished building a new design and getting ready to mount them up soon and test drive them.

its kind of hard to tell in this pic but these skis also have about a 13 meter radius. should be an awesome all-mountain ski, more tailored towards float skiing. "a powder carver"

im brewing on some ideas for a mountaineering ski, and wondering how skinny i can go. it looks like dynafit binding can be on as skinny of a ski as like 70mm underfoot or even a bit less. ahh shit, thats going back to the 90s! i want a small radius too but dont need a big tip, what do you thin about these dimensions:

105, 85, 112?

The tip isnt that much wider than the tail, i tapered the tip almost straight from where the rocker starts. i donno, am i killing my desired small radius with the tip being too narrow? or is the rocker tip going to add to the radius and give me a tight radius for slalom turns that i want?

PTTR · Post by **PTTR** » Mon Mar 31, 2014 10:30 am

The shortest radius I have ever built on a grownup ski is 10 meters. It is the funnest skis ever on ice and hard packed. it throws you around. I don't know if I could handle shorter with my tele bindings but I guess you could go even shorter with alpine. It has an aggressive, but short, tip rocker and some extra features, but most important a very short radius.

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But as to the question of where to put the widest point (end of sidecut) and start of rocker I am in favor of having the sidecut extend into the rocker. It gets the ski so turn so much quicker and get a lot livelier.

jono · Post by **jono** » Tue Apr 01, 2014 7:32 pm

I have been delving into ski designs with rocker, taper and camber/reverse camber.
I usually adhere to the 55%/BCL/45% when mounting bindings. My tapers are usually just a cessation of sidecut with a very subtle narrowing that ends in a rounder tip.
I just eyeballed the sidecuts so I am not sure what radius they are. Ski 1 is around 21m, ski 2 is maybe around 23m and ski 3 is about 32m.

Ski 1(2011):began as 160/114/140 modified to 136/114/125,183cm base material length, poplar core with triaxial glass, carbon stringers kevlar mat and clear hdpe topsheets.

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traditional camber with early rise tip/slight rise for tail
Stiff overall/about as stiff as my super G skis
Very hooky until taper was added to tips and tails. After this they skied well on groomers and crud but were too stiff for powder/moguls/etc.

Ski 2(2012/2013):122/99/112, 175cm base material length, doug fir veneer core with additional layers of triaxial glass, carbon stringers, kevlar mat and leaf spring of maple skateboard veneers.

made in same base mold as Ski 1 but with extra tail rise
Very soft tail and tip sections/quite stiff in camber section. Boot center is 52% from front of camber section and 48% from rear of camber section.
Not hooky at all, tip rocker allows for easy turn initiation, stiff camber section makes for solid carving at high speeds. Skis like a slalom ski. Tip rocker makes one feel a step behind in moguls (tips don't dive/search for next bump). Great ski for intermediate skiers. Skis ok in powder, tips rise nicely but stiff camber section can lead to tips diving in deep conditions. Soft forgiving tails.

Ski 3(2013):145/122/130, 183cm base material length, doug fir/fir cores with quadraxial glass, carbon stringers and kevlar mat with maple topsheet.
Slight pin tail on these. I made a template lengthwise of 1/2 a ski, duplicated it, then I made a final template by keeping the tails of the two half templates together while splitting the tip by a cm or so.
Full reverse camber
medium stiff (similar to explosiv)
Sidecut roughly matches camber Like 4frnt hoji/renegade.
Metal edges terminate 1cm past taper on both ends 140cm edge length Tip taper length is 275 mm, tail taper length is 170mm

This ski has become daily driver for me. When put on edge they rail on groomers. In crud they are powerful and easy to ski. I have skied these in steep couloirs and they maintain edge contact (because of sweet spot between sidecut and camber). They bite into ice and have not required much detuning. In powder they are in their true element and because of stiffness/shape/camber they like to go fast. Good floatation and easy to pivot in tight spots. The only time they get hooky is when they are weighted to the back and over turned in powder at speed. In this situation they want to hook back up the hill. Not for moguls unless I want to power straight through them.
This use of rocker/full reverse camber feels the most natural to me of the three pairs. It is due to the subtlety of the rocker, the stiffness and the sweet spot in the relationship of camber to sidecut. I have had to alter my technique to a more side to side turny type of skiing. Turns are initiated by going on edge in a centered stance and not through tip pressure. This centered approach leads to less fatigue. The reverse camber allows more forgiveness in landings. Overall these are my favorite skis right now.
The reason these skis work so well is because of the resonance between the sidecut and reverse camber, the stiffness of the ski and the tapered ends/terminated edges.

PTTR · Post by **PTTR** » Wed Apr 02, 2014 10:52 am

As an open question to all you wise people
what is the main point in having a reversed sidecut in the tip? I have built a few skis with it but I like the ones with a longer sidecut better in all conditions.

Design example:
an all mountain ski with camber under foot and a rocker front.
With a "normal" sidecut you get a longer active edge and a wider nose. floats better and carves better. why cut the nose? saving weight?
everyone around me seems to like them but I just don't get it. what are your thoughts about it?

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Ski design points and concepts

Ski design points and concepts