Comparison of Ski Dimensions for Manufactured Skis

by Jed Simpson
(forum login: hose-man)

November 11, 2005

Disclaimer: Contributed articles express the views of the author, not necessarily the views of SkiBuilders.com.  SkiBuilders.com accepts no liability for the content of this document, or for the consequences of any actions taken on the basis of the information provided.

Overview

This article studies trends in ski dimensions for manufactured skis.  Data was compiled from many manufacturers.  The results presented here can be used as a guide for designing skis.

So, What's the Problem?

Let's face it, ski design as most of us SkiBuilders have experienced is a complicated process.  A builder has to consider what materials to use, the profile of the core, the appropriate amount of camber (if there is such a thing), and, of course, the shape of the ski.  All these design issues can be complicated, and even worse, they can be coupled -- changing one aspect of a design can drastically affect something else. 

To help clear some of the smoke, I decided to compare and study ski dimensions for manufactured skis.  The motivation to do this came when I was trying to decide how much narrower the tail of a ski I was designing should be compared to the tip.   I conjectured there was probably some rule of thumb for this so I started studying existing skis.  I looked at websites and read gear guides, but at some point I was so overwhelmed by the volume of information, and I felt the need to compile it into a more manageable format and present it in hopes that it will be useful.

I started by collecting tons of data and archiving it in MS Excel.  The first resource was from the SKIING Magazine’s Gear Guide because it seemed very complete.  The review even listed side-cut geometry for skis.  Many of the manufacturer’s websites don’t even list side-cut info, so this was valuable information.  Afterwards, I consulted Couloir Magazine’s Gear Guide.  To complete my list, I filled in the missing models from the manufacturer’s websites and added some smaller companies listed on SkiBuilders.com (see the links page).  Additionally, I included some skis build by the Kams and Kelvin.

To help simplify this endeavor I limited my data collection to mid-fats and fats.  These were the shapes of skis I wanted to design and build.  Specifically, I targeted greater-than 80mm waist skis, but the ski mags had some all terrain type skis which were down in the 70mm range which I included for reference.

After some work, I ended up with a list of 104 skis.  The numbers listed in the Excel spreadsheet didn't really tell me much at first so I started sorting the data.  However, the volume of information was still too vast and further analysis was required.  Here's the list (you can download the Excel file by clicking here; the data set available here has a few of my formulas applied.   These display the tip/tail taper, and the side-cut depth.   Once you’ve downloaded it you can apply any formulas you’d like to view even more potentially useless data.):

Additional columns of data were added.  For example, I divided the tail width by the tip width, then subtracted the result from one.  This gave me a usable measure for percentage of taper from tip-to-tail measurement.  Was this the data I was after?   Naturally this is where things started getting even more interesting.   I learned to set up a chart in Excel. I expected to see that as skis got wider they increased in taper.   This would help keep the tip up in the powder.  Here is what I saw:

There is really no rhyme or reason to the application of taper it seems.   Based on the figure, the only conclusion I can draw is that, with a few exceptions, the taper is between 5% and 13% from tip to tail.  But what about the exceptions?  The Karhu PFD and the Volkl Sumo are at opposite ends of the taper spectrum from the Prior Doughboy which all are in the Top 10 widest skis!.   Two of the skis from the gallery of this site are among those with the least taper as well.  (the Tao and the Klown Whacker)

What other conclusions can we draw?

The graph above shows how the tip and tail widths react to the trend of increasing widths underfoot.   Notice that the ratio of tip-to-waist width generally shrinks as the skis get wider.  The more important trend might just be in the lack of a clear trend.  The way that the tip and tail line jump up and down tells me that in any given waist width there is a ski with a lot of side-cut and one with less side-cut.   Maybe not from the same manufacturer, but they’re out there.    The industry has definitely not homogenized.   The ski that creates the pinch in the graph at about the 104mm mark on the x-axis is the SB Tao!  The Shit and the Goode Carbon 116 are similarly straight and wide.   They are the next two pinches at 111mm and 116mm along the horizontal axis.  Naturally there are going to be some really straight wide skis and of course there are some inverse side-cut skis.

Here is the same data as above but with side-cut depth on the horizontal axis: 

The overall trend above shows what we all already know, side-cut usually decreases as width increases.

Most of the skis in the data set have side-cut depths from 10-15mm and the side-cut is generally deeper for narrower skis.

What have I figured out?

I learned that there aren’t many rules-of-thumb to go by in the ski industry.  I think that there are different strokes for different folk as far as ski technology goes, and each combination of geometry is probably just right for someone out there, but not everybody.  Some points:

• The range for tip to tail taper is 5%-13%

• The typical sidecut is 10mm-17mm

I was surprised to learn that even within the same ski category for the same brand there are significantly different geometries.  For instance, consider the side-cut radius.   Most manufacturers use the same tip/waist/tail dimensions for all lengths of one model of ski.   This results in a different turning radius for each length.   How can these ski’s perform similarly enough to be considered the same model?   Shouldn’t the radius, waist width and flex be maintained while varying the tip and tail dimensions?   Wouldn’t that make more sense?   Do you like how my conclusion paragraph is full of questions?   That sort of speaks for this entire research project.

While I don’t feel like I wasted my time on this project, I really didn’t get the resolution I was hoping for.   There are no hard and fast relationships between dimensions of skis.   I will likely return to this resource with each new ski design I create to compare it to what the industry is producing.