Test Procedure. All strings were tensioned to 62 pounds and allowed to sit for 200 seconds. Then the string was hit five times with a force equivalent to hitting a 120 mph serve. The tension loss represents the total amount of the relaxation over both time and impact. The stiffness value is a calculation derived from the amount of force created at impact to stretch the string. Lower values represent softer strings and lower impact forces. Higher values represent stiffer strings and higher impact forces.
But this is only one piece of the puzzle. Sure I am not arguing the softness. First it is an 18-gauge string. Thinner strings will be softer. It this test number import, sure.
depends on what is important to you. Softness, like you stated above both TW's string database and usrsa (tennis mag) document their dynamic stiffness. Now if you do a comparison, you will find TW dynamic stiffness is higher. Both still in the range of 156 for usrsa and about 180 for TW. They both have different test process. So in order to be objective it is important to compile and analyze all the data.
So going back too important. Why is this “important”, you really did not state clearly why?
So let me do so more mind reading again.
If the importance is solo stiffness. Sure it is important if you are seeking an arm friendly solution for a client. But is that it, no. It should not be.
It is a start. It is a good start thou to narrow down some options for someone.
It is the first place to start (stiffness value /dynamic) for someone. Especially if you need to find them a comparable string.
But before I write a book. All I driving at there are much more factors to equate in.
The Frame, The String Pattern, Tension loss, Targeted String Tension, Player's Swing (fast, med, slow). these are a few key elements that should be factored in.
String Breaker / Durability
String Life (goes dead ~)
So to end to the importance factor, it not the stiffness value ...the importance goes to the player.
Getting them the very best string solution that complements their frame, physical capabilities, game, level, mechanics and more (the more you know helps) ...
Example: ok this a soft string. Important yes..ok let’s string it up on my 14 year old sons frame. Hmm nope...
Reading other threads and people's opinions, I've heard that if I string my polys at a higher tension like 60 lbs, I would lose tension much faster than stringing at like 50 lbs initially, is this true?