Point Of Diminishing Returns With Regards To Ski Length

Been wondering this myself. Pre-shaped days I had skis at 190cm, the theory being that you bought the longest you could handle. Today I can get the same stability on shorter skis, but why wouldn't I still want 190 cm skis? I'd get better stability, more float and easier turning in the same length.

we have couple member of the PSIA Dev team on our staff and they are quite often far from the best our weekly ski bum GS races. the best guys in that race are just plain stronger more aggresive and willing to run a much straighter line and skid if need to. The majority of them regardless of their own size use 188-194 on a course that is flatter and tighter turns than your average WC Gs course.  Meaning that lengths matters and long skis truck, short skis suck.

I would say if your just tooling around at speed, but not at "crazy Super G speeds", then yes, there is no need to go long; about 185 - 190 cm should be good to go.  If you don't care about making time on a SL course or making itsy-bitsy turns at low speeds, there is no need to go shorter either.

Ken seems to me, that you are ready for D2's SL in 165, or any other ski in that category........ Everything comes to ability. The rest is just in your mind..

Do you really think, that 170's will give more advantage over 165,I don' think so. The D2 SL/165 skis are incredibly  stable at speed.

Look at the vid : K. Pallander on short SL skis ripping it fast ..

Don't forget that course designers put turns on courses to challenge the limits of the equipment and skiers.  In order to bend a ski's forebody into a tighter turn requires not only more sideways force at the tip (even the lightest FIS skiers have sufficient centrifugal forces to do this), but also requires more into-the-slope force.  Gravity supplies the downward component of that force.  The point at which a ski stiff enough to transmit significant force to the tip starts having not enough downward force due to gravity for a skier of our (your's and mine) weight to make a very tight GS turn is about 190 cm.  Using a softer ski helps a little, but has it's own problems; if your blasting high speed GS turns, you really don't want a soft ski (trust me, I'm a Doctor (Ph.D.) .

The question now becomes, well if you have extra weight, why not go longer.  Let's look at what you get by going longer (assuming you have the extra mass).

1.  Ability to bend that longer ski into the same tight turn as a lighter skier on a shorter ski, due to sufficient weight on the tip:  Loose something with the longer ski, but can afford the loss 'cause you can still make the turn, but most would rather keep the minimum length and add a safety margin with a minimum length ski..

2. Added vibrational stability: not really a factor; Modern SL skis are vibrationally stable enough for a hack like me at GS speeds and above, I'm sure FIS skiers don't have any problem with it.

3.  Added mass and thus slower response to inputs, particularly noticeable in recovery moves or sudden unexpected in-air redirections.  Big loss.

4.  Fore aft balance stability in response to bumps and bump absorption.  Gain something by going longer, but it's easier to ski the minimum length and live with the added difficulty than it is to make the longer ski go around the shortest corner.

5. Ability to carve a longer radius turn.  Strictly a function of turn radius, but Turn Radius does seem to go along with the longer ski.  This is the one place where a longer ski, because of its coincident longer turn radius, will be faster on longer turns, but it comes at a cost.  The cost is that the longer turn radius means the ski must be tipped more to maintain a given radius and boot-out becomes a problem on smaller turns.

It's a trade off between the advantages and disadvantages, and the determining factor for FIS races seems to be the shortest turns on the course at the moment. 

If you don't have to make those turns, you can go a little longer than what you would use on the FIS course and reap the benefits.

Quote:

Originally Posted by L&AirC 

 

Ghost,

I knew you would say "go long".  185 -190 is crazy long to me.  Can I ski a 185; sure.  Will it be fun; at times but not as an all mountain ski.

 

I was really hoping you would put your engineering hat on and come up with the math (hieght * weight / bsl + snow temp = the sq root of the co sign of the hipotenuse of the ski length).

 

At some point you don't need all the length.  Isn't part of the reason the the FIS rules were changed to longer skis to make it safer for skiers?  Maybe I'm reading it wrong and maybe it is strictly Turn Radius that matters.  The current FIS ski parameters makes skidding a requirement on some turns.

 

A few years ago people were winning competitions on shorter skis than they are winning on now, so when the rules allowed shorter skis, they went shorter.  The Elan GSX skis I have were FIS leagal when they were made (2003 model).  Now they aren't even FIS legal for women.

 

I would also throw out that there are women that are bigger and stronger than me.  Do I still need to be on a longer higher TR ski?  At some point, no matter your sex, and as long as there aren't any ability limitations, at some point skis become too long.

 

Ken
 

 

 

I took a long time posting; and this wasn't here when I started.

There is a point when skis become too long.  It's about 190 cm  (assuming you're doing everything right and you don't have to make a gate designed for shorter skis than are allowed in the race).

The advantage in for-aft balance control going over bumps and making recoveries is something that you can give away and live without in competition, it's a luxury that you may or may not be able to live without when blasting an unprepared surface while free skiing, but one I would want to have.

The turn radius is key.  There is a great feeling of making a locked-in carved turn that you just don't get on a long radius turn on hard surfaces with a short radius ski.  The cost of that feeling is the long radius ski won't be able to make a locked-in SL turn.  I would say choose according to what you enjoy the most.   For me, I would ideally want to have a pair  (one ski for each foot) of SL skis,  a pair GS skis and a pair of  Speed skis (currently without SL due to donating SL ski to son). 

For a SL ski I find 165 cm is fine.  For GS speeds and turn radii I like 185 to 190.  My speed skis are old-school so their length is perhaps not germane to the discussion, but I do notice a discomforting lack of grip and a desire for more sand in my pockets on some gs turns while free skiing  (at SG speeds of course ) at their 208 cm length, but the 205s (I think...memory fails me here) they made at the time just didn't have the vibrational stability I wanted at speed (I doubt that would be a problem today judging by the SL offerings), I opted out of the 215 length, not because I was able to discern the lack of grip on turns back then, but because of the severe thigh burn experienced after blasting through a long mogul run at Tremblant ( I suck at moguls now, but didn't even have a clue back then).
 

Quote:

Originally Posted by L&AirC 

BPA,

 

I know what people do.  What I'm asking for is why other than that's what all the kids are doing.  If the skis are all 188-194, they are probably FIS.  You can't tell me that someone that is 5'6" and 180# on Fischer WC 188's and someone that is 6'2" and 220# on the same ski are getting the same thing out the ski for the effort put in.  The 5'6" person has to be working a lot harder.  Why should a 5'6" person buy a ski that long other than they are FIS if they work just as well for someone taller and heavier.  If the 188 is right for the smaller skier above, shouldn't the larger skier want a ski that is proportionally fit?  Most FIS GS skis are all within a couple inches (even Fischer's GS WC only spread 4 inches) of each other but most skiers aren't.  The forces and leverage each is able to apply to a ski have to vary quite a bit.

 

So, if there aren't any FIS rules, how do you figure the optimal ski length?

There are no ski rules at our local series, the short skis are just slow regardless of skier size. I'm thinking of one guy in particular that is the size you stated and skis a 194 or something close to it.

On the other hand though, are you asking about racing or just ripping around? I know that I am fastest on a longer GS ski, but it's not really what I want to be on. I think the answer to your question is 176-180 depending on the ski.

A longer ski provides more stability than an equivalent shorter one.  However, the key factor is the carving ability of the operator.  Many world-class skiers can carve the longest lengths of a given discipline's ski dimensions cleanly, but you find even some of them going a length or two shorter.  The rest of us need to be on a length in a given ski that we ourselves can carve cleanly (assuming speed and control in a racecourse is the goal).

That is why you find it hard to locate the "perfect" formula for length; all the other factors of the ski's characteristics come into play, not the least of which are sidecut radius, torsional rigidity, longitudinal flexibility, etc., combined with the operator's skill.  Like snowflakes, no two skier/ski combinations are exactly alike.  Nor are all skiers aspiring to carve cleany, and many of them find it easier to skid a shorter ski than a longer one.

Unfortunately length is just one parameter to consider. Length alone cannot be the only determining factor. Different skis in similar lengths are not always comparable. And then the same ski in different lenghts have different flex patterns, torsional rigidity and overall stiffnness. I think it also is vea very comparative issue. It deoends on what you skied on just before the ski you are currently demoing and what you get used to skiing on.

Unfortuantley the only real way to figure it out is to demo, demo demo. And then it also depends on where you ski.

My everyday ski last season was a Non-FIS Atomic d2 GS in a 179cm. 18.4 M radius. For groomers at my home mountain this is the perfect GS ski. But when I took them to Whislter-Blackcomb, although fun, I was really wishing I was on a 186 or 191. they were just not long enough for the wide open groomers up there.And the snow was extrememly fast!

By the way when demoing and deciding on this ski, I skied it back to back with the Head 1.speed in a 180 and the Fischer RC4 Pro in a 175cm. (when I wnet to the fischer booth, they had the Pro 175cm hidden and would only let certain folks even ski on it!) I aksed for a 180 and they said try the 175. When I came back, they said, you don't want a 180 do you. I said hell no! The 175 was 2X4 stiif and they said the 180 is stiffer!

Both the Head and the Fischer were way too stiff longitudinally. When I got on the d2, I could not beleive the difference and it had better edge hold and was smoother and easier to initiate then the other 2 skis!  The Head in a 180 is 18M, The fischer in a 175 is a 17M.

You have longitudinal stiffnees, torsional stiffness,longitudinal flex pattern and taper angle.

The reason SL skis are slower in a Gs course is not the length nor stability, it is the turn radius and shape. You are forced to ski more across the hill then down the hill, simply due to the shape of the ski. taper angle also comes into play here. And slalom skis have a much smaller taper angle (how much tail is wider then waist)  (More taper angle means the waist to tail dimension is more tapered) is more tapered then does most GS skis. So not only does radius come into play but so does shape.

As far as Races courses pushing the limits of equipment, I can't totally disagree with that, but there are rules that dictate the course set to a large degree based on total vertical drop and number of gates.  So some of it is a function of the course rules and then some is dictated by terrain and minimum distances between the gates. Course setters do not have free reign to simply torture the racers with absurd sets at the outside limits of the equipment.  

It is a process unfortunately that depends on many variables. Ya just gotta try some different things and see what appeals to you.

Width matters more than length. 

Ask any woman.

I'm not an engineer, so someone please correct me if this is BS.

Anyhow, regardless of radius, a longer ski will produce a more forceful/longer-propelling slingshot effect going out of the turn.  If you have skiblades with a 27 radius, then 188 GS skis with a 27 radius (both with same construction), the 188 is going to be faster.

I also heard less sidecut=more stability because the more a ski looks like an hourglass, the flimsier it is (within any given line, other things being equal).

Wouldn't a longer ski get deflected more at either end if sufficient pressure at all times isn't applied too though? I.e the further away from the centre of a circle, the less force is required to rotate the centre of it etc which would be your foot in this case?

Not so important when racing as edge pressure and balance are usually at expert levels but for all mountain use I'd imagine in rough stuff length doesn't always help depending on the weight of the skier and the ski stiffness or forgiveness. Still length can provide extra float too depending on the flex also.

The new skis now with riser, rocker etc aren't really as long as they sound either so maybe the effective length should be quoted as well as the total ski length these days....?

P.S The post above, also stability vs sidecut would be more around what's touching the ground I would think. A ski with an aggressive sidecut when not edged is fighting the width differance between the tips and centres more than a straighter shape is when running flat or even really when not fully bent on an edge. I ski short skis with a small radius and on cat tracks at speed it's just safer to feather from edge to edge than hold one pressured edge or run them flat. The wide tip/tails to middle ratio make pivoting and slipping a bit more tricky too as any angulation hooks up and starts a turn. Still love the fighter pilot feel in the turns though

Quote:

Originally Posted by L&AirC 

This is great information and I appreciate everyone taking the time to make such detailed answers.   I might be chasing the holy grail (more than likely my tail) but I would like to take one more stab at this. 

 

In my head, and that might be the only place it exists, there should be something for ski length like there is for binding tension; height, weight, bsl and skier type and it spits out a number.  Why can't it be height, weight, ability and ski type and it spits out a length?  Even in the Fischer tech manual, for each ski type and each skier group (man, woman, junior), it gives a minimum and maximum length but even with that, it's still vague (i.e a race ski for a man should be somewhere between your lower shoulder and 6 inches over your head - that's about 50 cm!).

 

This thread wasn't meant to be about picking the "ski".  It was intentioned more towards, once you pick the ski (considered all parameters and know what particular job you want the ski to do), how do you make sure you are getting the right length in that ski that you want?  Is the only way to demo every ski out there first to find the ski and then demo every length?  That would ensure you get exactly what you're looking for but there are some general rules that let you skip several of the steps.

 

The more I study this I'm really starting to think that ski stiffness and TR are probably more of a concern than length.  At least for me.  I think I'm just going back to my original way: eany meany shiscka beany ah ba boo.  Achi kotchy dominotchy out goes Y-O-U! 

 

Thanks,

Ken

basically you have techno nerded yourself into obscurity. 

the thing is different length skis are going accel at different things. It why I own skis from 165 to 192 and width from 65-120.  There are alot of skis I could see owning multiple lengths in the same exact skis because of how different the longer vs shorter ones feel.

Take the Bonafide in 180cm it a pretty easy going 98 mm ski that could truly ski anything you put in front of it. For me I can easily find a speed limit in chopped snow on it. The 187 make skiing chopped snow easier for me and powder slightly easier but for sure is more work skiing tight bump runs on it. IMO there is no magically ski length for anyone because every individual could probably find reasons to buy either(or multiple ) size skis.

Wrong on all counts!
 

Quote:

Originally Posted by BlueSquare 

I'm not an engineer, so someone please correct me if this is BS.

 

Anyhow, regardless of radius, a longer ski will produce a more forceful/longer-propelling slingshot effect going out of the turn.  If you have skiblades with a 27 radius, then 188 GS skis with a 27 radius (both with same construction), the 188 is going to be faster.

 

I also heard less sidecut=more stability because the more a ski looks like an hourglass, the flimsier it is (within any given line, other things being equal).

delete

Quote:

Originally Posted by BlueSquare 

So short people should buy shorter skis but with longer radii to go faster?

Skill is going to do way more than ski length when it comes to 'speed', but there is a reason that the entire WC is the size of football players.

L&AirC:

If you are looking for a NASTAR recommendation, my advice is as follows:

Handicap 0-10:  Choose a ski with 19-24M Radius that is the longest you can cleanly carve (175-183 depending on your height).  Longer is overkill for NASTAR, as is a 27M radius (unless literally you are a pro/FIS ski racer)

Handicap 10-20:  Choose a ski with a 15-18M radius that is up to 180 cm long (prolly get something as tall as you)

Handicap 20+: Ski length and specs doesn't matter as much (just ski something you enjoy and are comfortable on).

When going faster (and over ruts, etc), longer skis offer more fore-aft balance/forgiveness.  FWIW, I've heard NASTAR racers usually wish they went a little longer when they bought cheater race skis.

Quote:

Originally Posted by L&AirC 

 

Other than eany meany miny mo, I'm really starting to think it is more about torsional stiffness Turn Radius anyway.

Ken

Or your weight vs ski length really. A persons height seems to always be used as the quasi fit for weight in this industry.

Some skis dimensions change to keep the TR the same as the ski length changes. The only other other change then in the ski can be it's stiffness to match the perceived skiers weight.

So any length in the same ski must surely be matched to a weight range to try and get the same feel for everyone skiing it surely? The same person skiing the same ski in different lenghts is just going to notice the TR change and a more solid GS like feel as it gets longer surely.

So are you really asking for a weight guide vs ski length as to what a person needs to be in order to get how the manufacturer intends a ski to perfom at it's best attributes etc?
 

Quote:

Originally Posted by snala 

Or your weight vs ski length really. A persons height seems to always be used as the quasi fit for weight in this industry.

Some skis dimensions change to keep the TR the same as the ski length changes. The only other other change then in the ski can be it's stiffness to match the perceived skiers weight.

So any length in the same ski must surely be matched to a weight range to try and get the same feel for everyone skiing it surely? The same person skiing the same ski in different lenghts is just going to notice the TR change and a more solid GS like feel as it gets longer surely.

 

So are you really asking for a weight guide vs ski length as to what a person needs to be in order to get how the manufacturer intends a ski to perfom at it's best attributes etc?
 

 

I thought taller people exert more of a lever-effect on their boot tongues (and thus tips of skis) and therefore have an easier time initiating turns with longer skis (and longer radius skis).  Obviously, as the skis are bent and the turn is developing, weight has more impact.  But I'm pretty sure the pressuring of the tip (and the tilting of the COM) is more profound in taller people.  Thus, it may be better to get a ski that is appropriate for height AND weight, as the two are both functions of force exerted on the tips during turn initiation and angular forces/momentum.

Quote:

Originally Posted by BushwackerinPA 

 

Take the Bonafide in 180cm it a pretty easy going 98 mm ski that could truly ski anything you put in front of it. For me I can easily find a speed limit in chopped snow on it. The 187 make skiing chopped snow easier for me and powder slightly easier but for sure is more work skiing tight bump runs on it. IMO there is no magically ski length for anyone because every individual could probably find reasons to buy either(or multiple ) size skis.

 

Quote:

Originally Posted by L&AirC 

 

However, I think you still missed the point of my thread.  It isn't why have skis of different lengths.  It is once you know what it is you want, how do you determine the perfect length?  Once you picked the perfect ski, lets say for weekend NASTAR (seems to be a fairly specific task), how do you know whether to buy that ski in a 170, 175, 182, 184, 188 etc.  In your last paragraph, you are describing using the ski for different things, hence the different lengths.

 

L&AirC, IMO your initial question is based on a weak premise, about FIS mandated lengths and shapes and stack heights being determined by - or somehow showing that there could be - an "optimal" physical design. And thus that there are diminishing returns as we move away from some "optimal" length. But designs are not optimal. Rather they correlate to averaged performance demands of various courses, safety concerns about same, and the politics of racing programs and ski making. So for instance, most SL racers would like to use shorter skis with deeper sidecuts. Won't happen because of concerns about leg injuries. Those specific issues, and their solutions, are only modestly correlated to NASTAR or club racing, and weakly to free skiing. (In general, short skis with deep sidecuts appear to be less knee friendly, but a lot of other variables, obviously.) We rec skiers do not have the luxury of having skis' flexes built to our styles and sizes unless we go to a handful of custom makers who mostly produce fatties. So we go for different lengths, widths, and models. And any choice we make involves tradeoffs, or diminishing returns for a given quality, if you want. When you're talking about length, IMO you're actually talking about flex. But there is no single quality that has some magic, top-of-the-heap effect on a single skier. 

Given this, BWPA's answer in fact is why there is no "perfect" length. Case in point: I weigh 7 lbs less than you. I have several "perfect" lengths depending on the loads being placed on the ski, which in turn are defined by the terrain I use it in, the speed I ski, and blah blah blah. I ski a FIS SL in men's 165, and a FIS GS in women's 181. My fav ski for NASTAR is either the SL or a 167 G-Power, although I wouldn't mind a cheater in the 170-175 range if I could afford a ski just for that. (Drooling over the 170 Stockli SLX.)  That length works best for me on a typical NASTAR course, although it's a bit intense for smaller eastern resorts. So point is, I don't "know" which length to buy, in the sense of my size and a model. No physics will help. I just know that various lengths have maximum utility for various missions, and for my size and style of skiing. 

Same argument, basically, for lateral resistance to bending, sidecut, you name it. Too tied up in personal variables to allow an optimum. Although I'd guess there are some basics: 1) Longer runs faster. 2) But longer is slower to respond. 3) So if the race is about response time, eg, slalom, go for as short as you can handle. If about stability at speed, go for as long as you can handle. 4) If at the speeds you race, you can't bend a ski enough longitudinally, or know it won't at the same time deform too much laterally, you're not gonna make the gates. Sierra Jim had a nice post a year or two ago about how in his opinion, the skis that were most popular were those that had harmonious longitudinal and lateral flexes, rather than say a ski that was a noodle front to back and like a steel beam side to side. Suspect the same applies to different brands of rec race skis, which is why there are so many different models.

Quote:

Originally Posted by L&AirC 

Everyone's reference point for skis, including manufacturers, starts with, pick a type, then how far up your body it stands (chin, top of head, nose etc).  That's what got me focusing on length.  Maybe my dreams of there being a "skiHarmony.com" have been dashed, but I still believe science can be applied, even though we don't know what it is yet.

 

Ken

 

 

I completely agree that there should be some science applied.  Much like people get custom fitted for golf clubs (head type, shaft, shaft length, shaft flex, kickpoint, swingweight, grip, grip width, lie angle, bounce angle) based on their height, ability, etc... well, skiing should be the same, allowing one to pick a "perfect combo" of length, stiffness, TR, etc.

There are endless possibilities for ski manufacturers, offering different flexes within lines, and other cool custom stuff that needs to happen.