Originally Posted by DavaiMarat
While I agree poly strings are stiff, it's not the inherent stiffness that creates the spin. I can string natural gut at 90 pounds and still not get a 'spin' friendly frame.
Look at Fed and Nadal, both who string in the low 50s and high 40's respectively. They have the two heaviest laden forehands on the tour. Do you think their string beds are harder then a multi done at 58lbs. As a stringer, I guarantee no.
Poly's are dead strings, that means they aren't very elastic. They absorb pace like a wet dish cloth. This helps reverse the incoming spin and increase dwell time. This combined with a vertical-friendly swing = lots of spin.
Bjorn Borg strung his tiny 65 sq. in. wood racquets with the super dense 18x20 string pattern (incredibly dense in a tiny head) with natural gut at 85lbs and got tremendous spin from it. His stringbed was as stiff as a wooden board. That resulted in more ball compression, and thus, more spin.
Nadal and Federer can string much lower because they use poly strings. Poly at 50lbs is about as stiff as natural gut at 90lbs., perhaps even stiffer, IMO. I can feel the stiffness of poly on my elbow at ANY tension. Heck, when I string poly on a dropweight stringer, the weight doesn't drop nor budge even a centimeter. With a multi, it will drop like 2 feet several times so I have to keep racheting. The difference in resiliency is like night and day.
It's not just the dwell time that creates the spin. It's the fact that a stiff stringbed causes the ball to flatten more against it. This allows a greater percentage of the ball's surface area to come into contact with more of the strings in the stringbed. Thus, when you swing vertically, you are "grabbing" more of the ball with more strings and each string is digging into the ball more. This allows you to transfer more rotational force to the ball resulting in more spin. This is why poly users feel more "bite" and hear a louder "pop" when they hit the ball than multi users do. That's the sound and feel of the ball flattening more against the stiff poly stringbed.