I have developed a fairly (to say the least) advanced string bed calculator that I thought that I would share some results from. I also made it into an iPhone/iPad app called stringBed. It uses a non-linear finite element model with about 700 elements to model the strings in a racquet. This means that you apply fairly large loads to the racquet and see how the strings deform and calculate the stiffness. There are some calculators and measurement tools around, e.g. Stringway. But they only work in the low deformation/linear range where the stiffness is independent of the string type. To some results: A 95 sq in racquet, 16x20 string pattern, 25 kg string tension. Two different strings: Babolat natural Gut 1.25 mm and Big Banger 1.25 mm, the string data taken from the USRSA string selector. If you apply increasing load levels in the middle of the racquet and plot it versus the deformation you get a curve like this: The load is in N(ewton) i.e. 1000 N is roughly 100 kg or 220 lb. If you look at stiffness (probably more interesting) when you increase the load you get a curve like like the one below. The stiffness is in N/mm which is equal to the kg/cm used by Stringway and others. As you can see from both curves the stiffness increases quite dramatically when the load goes up (this is total stiffness, not incremental which is even higher). This is not surprising since it is typical for cable structures. Another thing to note is that the string bed stiffness for small loads is independent of the string type and dimension, but vary quite a lot when the load increases. Neither this is strange, but important since it emphasizes that it could be "dangerous" to only look at small deformations. The load levels here are realistic for a tennis game, even though you have to be really good to achieve the highest loads in the curve. If you instead look at how the tension influences the stiffness for two different load levels. You get curves like this: The relation between tension and stiffness seems to be linear, but the slope is less than 1, i.e. doubling the tension doesn't double the stiffness. This is especially true for the high load. Interesting to note is also that the two string types are almost identical at 250 N, whereas at 1 500 N the 16 kg poly is as stiff as the 28 kg gut. There are lot more to be said about this, but I leave it open for discussion here and will come back later with more results. /Sten _________________________________________________ racquetTune, stringBed and swingTool tennis apps for the iPhone.