Adding a little bit to what Marius said...
The goal of our measurement technique is to measure the
fundamental properties of the skis. This is different than measuring the result of some applied loads (e.g., measuring the distance that the ski deflects for a given weight in a 3 point test). The reason we do these measurements is that we want to be able to predict any load conditions that a ski can be put through like skiing on ice (load mostly underfoot), skiing in deep powder (load distributed along the ski), landing and having only the tail touch the snow, having the ski loaded at any edge angle, etc. By measuring the EI (bending stiffness) and GJ (torsional stiffness) along the full length of a ski, we can simulate any load case that we want. EI and GJ are like the spring rate/constant of a spring (i.e., with units of in/lbs or mm/kg like Dakine did). It is the ratio of displacement by the load you apply to it. Loading conditions (also called boundary conditions) include snow and the forces applied by the skier. It is not trivial to represent these conditions properly. There are many type of snow, and even the simplest type requires complex models. Modelling a skier also has some challenges, and it depends on your mass, your ability (i.e., can you pull a 3g turn?) and your style (how you use your skis).
But in all cases, as Noodler pointed out, if you have access to these measurements for the skis that you tried, it is easy to start understanding where the "character" of a ski is coming from. It is very easy with these data to find similar skis. It is also relatively easy to ask for "a little bit more/less of X than ski Y" if you know which parameter makes for what. For exemple, the graph that Marius posted show three somewhat similar skis. You see with a trained eye that :
- 1st graph: The front running length of the Elite Long Turn Ti is about 5 cm longer even if the ski is only a 2 cm longer ski (177 vs 175).
- 2nd graph: The sidecut of the of the Elite Long Turn Ti is larger than the two other. You can also see that all of these skis have their widest front point up in the air, so as you edge the ski more and more, you will get more tip engagement.
- 3rd graph: The bending stiffness distributions (EI) are quite similar (this is often the case for "general public" ski), but the long turn and multi turn have stiffer tails, so they will provide more support (e.g., more kick/pop at the end of a turn). Note that this graph is not a "displacement under a load" kind of curve. It is the spring rate of the ski at that location on the ski.
- 4th graph: The torsional stiffness distributions (GJ) show that the Multi Turn and Plus TI are about 30% softer, with the multi turn "carbon" being even softer in the tip/tail. We typically see the most variation in these measurements, but it also seems to be the property to which skiers are the most sensitive to. This is also the measurement that nobody else really talk about or have numbers about! A high torsional stiffness make for a very precise ski. It will do well on ice. It will track well, but you need to be able to place the ski where you want it to go otherwise you will pay for it. You also need to have good technique to release the edges. Too much torsional stiffness can also make for a "harsh" ride (kind of like if the edge haven't been detuned). A softer ski will be easier to slide sideways and be more playful. We see that a lot in beginners skis, but even "expert" park skis are torsionally soft.
That is a quick summary for the averaged values. It works quite well if the skis that you are comparing are somewhat similar to start with. This is often the case when you shop for a certain type of ski. You can also dig deeper and look at the local properties to know how different part of a ski will behave during different part of a turn.
You can't always look at each property individually however. For example, if you are interested in the speed limit of a ski. Many people think that it is related, in part, to how much "preload" pressure you have on the tip, which will prevent the tip from flapping up in the air when you hit little bumps at speed. The more pressure you have, the faster you can go without the tip flapping. The pressure on the tip depends on the bending stiffness, the camber, the length of the ski, the sidecut, the edge angle, etc. This gets complicated, but it is not magic!
We can predict that in our models. We are still building up our knowledge about the interplay between all these measurement. We welcome any input from the community about which "feelings" are important to you in a ski. If you tell us what is important to you, we can try to model that with our data/models!
There are probably hundreds of ways you can use to measure these properties. There are dozen of undergraduate (and PhD) thesis about this going back at least 50 years. This is not new. However, we specialize in doing all these measurements very fast (and continuously along the full length of the ski). Most techniques that we know of can take quite a long time to do so, require multiple machines and only take part of the measurements needed. Our goal is to measure the full fundamental properties of
all the skis in the world, which means all models and all lengths. Measuring the different length is quite important as the scaling of EI/GJ with length is not uniform across industry (and other properties can also change too like width, sidecut, etc). We are partnering with museums, individual collectors, shops and manufacturers to have access to as many skis as we can. We return them unharmed as we [somewhat unfortunately] don't need to ski them have a pretty good idea of how they will ski. ;-)
To get back to the original thread... To get a more complete picture of the difference between these skis, it would be great to compare the local values of the bending stiffness and also torsional stiffness if you can. However, you seem to already have measured quite a big difference in their bending stiffness. That might be a cue. We often see that the torsional stiffness scales with bending stiffness, as many in the industry use the same tri-axial fiber in their construction and adjust the core thickness to scale both EI and GJ together. But who knows, you could have a case of soft flexing but torsionally rigid ski. They are not as common (as you need to think a little more about the laminate and often introduce additional layers), but it is my favorite kind of ski. It fit my style quite well (i.e., lot of small precise turns).
If you want to dig deeper, we could probably measure your skis... we unfortunately don't have them in our database. We would love to better represent smaller manufacturers.
Alexis
