Exactly, absolute spin RPM by itself is not an interesting value at all and therefore I was talking in my post about spin production instead of pure RPM. In other words, for a given spin production technique one can put more spin on the ball in order for it to land within court bounds with tighter string bed. Loweing string tension leads to either altering one's technique in order to produce same RPM or to reducing the RPM if one doesn't alter the technique. And I don't think messing with the technique is a good thing, hence less spin becomes the only viable option. Anyway, What is the use of asserting that one can put same spin with loose string bed if the ball is going to hit the fance as a result? After all tennis is a game with some rules and not just a physical phenomenon. BTW, I did read that research study, I think it was posted here not so long ago.