Yeah I know, pretty dramatic stuff. Of all the slow mo vids and photos I've seen, that one shows the most extreme ball deformation. Ball compression to about 45% original size is much more typical. I'm curious about the ball velocity, and impact conditions as well. Regarding the Tretorn Micro X balls, they aren't the limp noodles that the phrase "pressureless" might imply. Rather than being gas injected like typical balls, that lose pressure every second of every minute, they are filled with millions of balloon like microcells, that don't leak. While you might find the Tretorns sanctioned for use once in a blue moon for tournament play, they are mainly used for ball machines, because they stay playable for a very long time. Based on the user feedback right here at TW, they play a bit like stiff, extra duty balls. Pure conjecture on my part, but I'm guessing that the ITF chose these balls for their tests, because they needed a tough felt to stand up to the machines that fire the balls, and they needed a ball that offered a solution to the problem of regular balls losing pressure so quickly.
Hi USCF2012 -
Yeah cool, sorry I cant give you the short answer you are looking for. That's actually like four separate questions all tangled up into one question. Some basic distinctions are needed first.
Although you have verbalized it as such, increased ball pocketing and increased dwell time are not always synonymous, in fact they are often inversely related. See my post #41, Para 1C for greater detail.
Ball pocketing, or more properly said, string bed deflection, is defined as the amount of deflection perpendicular
to the string plane. This is not associated with spin enhancement. See my post #41 2A for greater detail.
Spin enhancement has been shown in recent years to be a product of two factors, ball-string friction and inter-string friction. Low inter-string friction promotes slide and snap back, parallel
to the string plane. This happens while the string bed is deflecting/pocketing, but the deflection backwards is not what generates the additional spin. The additional spin is generated by the string brushing up the back of the ball in the vertical plane (on a groundstroke). See links in Post #41 2B for greater detail.
I don't ever argue what people feel/observe on the court. However, with regards to Kevlar offering more spin enhancement than poly, I invite you to consider that:
The 3 most credible racquet technicians on the planet, ie. the Holy Trinity of Jay, Nate, and Warren, all say otherwise.
The select few who study, and publish racquet physics for a living... Brody, Cross, Lindsey, all say otherwise.
Then there is the pro tour. Not many supporters there. As Pv Audio has noted, Agassi was the last Kevlar user of any note.
I used Kevlar myself for a few years circa 2001-2002. I was too was pretty convinced at the time I'd found the ultimate spin machine. I think I understand now why I thought that. There is a very plausible explanation to why you feel what you feel with Kevlar, why you might perceive it to be more spin friendly than poly. It isn't texture, or dwell, or increased ball grip. Perhaps it's just that it's very low powered. It's very stiff, in fact, 2-3 times stiffer that the stiffest poly. This just means you have less fear of hitting long. You swing faster when you don't fear hitting long. Swinging faster creates more spin. Your stroke has changed because of the string, but the additional spin is coming from your stroke, not the string itself. In lab experiments, they have proven conclusively that irrespective of player technique, certain strings produce more spin than others. That's the central issue at hand. Kevlar is no where near the top of that list. Pretty consistently, it's slippery textured poly as a full bed, or Gut/Poly that tops the spin charts.
What's ironic, is that for years following the The University Of Sheffield testing done by Goodwill and Hawke circa 2004, the entire racquet physics community (excepting our very own TravlerAJM, who knew better) came to the conclusion that strings don't make any difference at all with regards to spin. That conclusion was 180 degrees opposite from what we were all experiencing on the court. More recent testing has only validated what players have known all along, that strings do make a difference with regards to spin. Even though we now have lab testing which validates the player experience, players are still skeptical of the dudes in the white lab coats, and perhaps rightly so.
I'm no braniac, I can barely add and subtract. Just know where to find the answers, just a dumb jock who prefers reading racquet physics to prescription sleep aids, and it works really well for that purpose. Haha.