A while back, Blister reader, Orest, posed this question in the comments section of a ski review, and we thought it was a topic worth discussing:
Q: I have always wondered how often manufacturers actually make their longer lengths stiffer with more metal, or is it something we all too often assume incorrectly?
Good question, Orest.
So we decided to put the question to a number of ski designers and builders, and to publish their answers here. Up first is one of the most obsessive ski builders we know, Scott Andrus.
Scott Andrus, Founder, ON3P Skis
A ski’s core profile holds the identity of the ski. While most manufacturers doing any notable volume have good access to various composites, metals, and core materials, the core profile of the ski is the element that gives the designer the most control over a ski’s flex.
Composites & metals are, on the other hand, used to make macro design changes. I can make a major flex change on a ski just by going from a 22 oz fiberglass to a 19 oz fiberglass. In most cases, those types of macro design modifications are too large to account for the flex variations desired between a 181 cm & 191 cm ski.
It also doesn’t make a lot of sense for a manufacturer to stock an excess amount of different composite weights — it isn’t practical in a production environment to be carrying 10 different fiberglass weights so you can solely use composites (or metal) to alter flex.
These length-based flex changes need to come from the ski’s design work itself. As a designer, the first thing you need to decide is how you scale sidecut & dimensions by length. You see some brands that will maintain dimensions over a size range, some who will scale skis proportionally, and some who just scale as they see fit (based upon their gut feeling on optimal performance).
At ON3P, we design all our skis based upon our most popular size within the range, then scale our sidecut / dimensions out proportionally. We want comparable performance and characteristics throughout a size range, and we’ve found the greatest consistency by designing a model off of our most popular size and then scaling up and down proportionally.
When accounting for flex between sizes, we’re then making appropriate thickness & length modifications to the ski’s core profile to adjust for the size change. And there is a performance characteristic taken into account here as well. While we want the flex characteristics to remain consistent between sizes, we do also need to acknowledge that we want a 171 cm ski to be softer flexing than a 191 cm ski. When we scale between sizes, we’re calculating the thickness for the flex output we want, and then we review those results by building, testing, skiing, and modifying the profile until we get a final ski flex.
In the most basic terms, a ski’s core thickness profile is the primary design element we use to determine a ski’s stiffness & flex.
It should also say, I wouldn’t be the least bit surprised if some manufacturers were just throwing additional composites in there and calling it a day. We see lazy design work pretty often.
Cyrus Schenck, Founder, Renoun Skis
I agree with Scott. Core thickness can be the easiest to change to dial a new ski length in. No one goes out and buys a thicker sheet of metal for the 191+cm – it would complicate the heck out of everything.
Even when we’re scaling up and down we find we don’t get it correct the first time. Starting with a 178cm ski, we scaled the length down to a 169 cm, and brought the core from 10.542 mm to 10.013 mm, and it wasn’t enough – the ski was still too stiff for a 169 cm. We played around with it until we found the appropriate flex for the shorter version.
Jed Yeiser, Head Ski Designer, K2 Skis
I think Scott’s answer pretty much nailed it — a ski’s construction (i.e., the materials used, and where those materials are in relation to one another) give a ski much of its character, so changing those materials between sizes really doesn’t make sense, as we try to preserve the same characteristics in all sizes of a model.
As far as scaling flex and stiffness between sizes, we keep the flex (and more importantly, the stiffness distribution) of our skis consistent throughout all sizes. Like most other manufacturers, we use the core thickness profile to make any changes to the ski’s flex and stiffness profile.
While simply adding more/stiffer material to a ski will stiffen the ski up, it doesn’t preserve the stiffness distribution of the ski, and that has drastic impacts on the way a ski performs.
Another issue with adding heavier materials is that it changes the location of the neutral axis of the ski, which can have pronounced impacts on break strength. This isn’t to say that you couldn’t use different materials and recalculate the core profile to get the correct stiffness distribution, but as I mentioned before, the ski will behave differently given the different properties of the materials used in the ski.
I do know of one (extremely popular) model from another manufacturer that does change the layup between its longest and shorter sizes (the 188 cm model has a different layup and is stiffer than the 180 and shorter sizes). I can only speculate as to why that change was made.
Luke Jacobson, CEO, Moment Skis
Core thickness is the way Moment and almost all manufacturers tweak the flex of the ski within a model size range.
The core is the heart of the ski and the first materials we consider to shape the way a ski feels since everything gets built around it. When we design a ski, we determine if we want it to be lively or damp, light for touring, or a slightly heavier crud buster, and many other variables. The core wood type, composites (e.g., the type of fiberglass, carbon, kevlar, etc) help push the ski design in one direction or the other.
When designing a new ski model we start by building the most popular size in the range that will fit the athlete, ambassador, and Moment design staff best to ensure we can properly test it. This usually ends up being a low 180 cm length in the men’s range and a low 170 cm range in the women’s collection. Once that size is dialed in, we work up and down in the size range to ensure a cohesive feel throughout the entire range, getting input from the athletes and ambassadors that ski size is intended to fit.
Typically when a ski gets shorter, you slim the entire width down by a few mm and make it slightly wider when making it longer. Additionally, the core is thickened or slimmed down to change the separation of the composites which in turn makes the ski stiffer or softer, this separation from the center line of the structure is one of the most powerful and easiest tweaks you can make in a ski design, but it takes a lot of time and revision to make it how you truly intend.
You also do not want to introduce unique materials like metal into different size lengths, because that would totally change the way the skis feel and acts. Additionally, if you don’t add metal and change the weight of the fiberglass, you are not only going to be be changing the longitudinal flex of the ski, but also the torsional rigidity…while the difference in length is a large change which could potentially warrant this design choice, the width changes are very small and would result in a non-cohesive feel. So in our opinion, a major composite change between sizes would also be a bad design choice.
Some manufacturers will make a series of skis they see fit for the mass market and make a stiffer “Ti Edition” (Ti=Titanal, which is really just an aluminum sheet with almost no titanium in the material regardless of the name) or sometimes a lighter edition for touring with some sort of carbon build which replaces a lot of the heavier fiberglass with more or all carbon.
At the end of the day there are a lot of ways you can change the design of a ski but its not always as easy as just “throwing some more __________ in there.” Beyond the material changes, you also need to change the the transition points and curves of these profiles along a shorter or longer distance. A lot of the time making a short ski’s flex profile exactly how we want it is more difficult than a long ski, because you need to spend a lot more time making all your profiles work in a more confined space.
This is a great topic point and I could go on and on about our opinions and how we address this here at Moment. So if anyone has anymore questions, please fire away. We love talking ski design.