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Old 09-19-2012, 05:10 AM   #28
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Join Date: Feb 2010
Location: Holland - Belgium
Posts: 695

Originally Posted by corners View Post
The sweetzones are primarily a function of swingweight, with twistweight and stiffness coming in a distant second and third. The TWU Power Potential data shows that there is a nice, tidy relationship between swingweight and Power Potential of 10 swingweight units = 1.0 Power Potential units. Looking only at the sweetzones (20%, 30%, 40%) makes it hard to compare sticks with very different swingweights. If you switch to the location view, you see that the 90 has Power Potential of 41.2% in the center of the stringbed and the 95, 38.8%. The swingweights of the specimens tested were 324 and 303, respectively. So we can add 2.1% to the 95's number to get 40.9%. In other words, this is what it would be if we added lead tape to bump the swingweight to 324. So matched, the 95's PP is slightly less than the 90, which is probably down to the slightly lower stiffness of the 95.

So the numbers are actually about what you'd expect. You can do the same addition at other impact zones above, below and to the sides of the stringbed center to project what the Power Potential would be with lead tape added, but it because a less precise approximation outside the center due to how twistweight and local stiffness change depending on lead tape location.

Anyway, Fed K's perceptions seem to belie all this, but then again he may be experiencing and reporting something quite different from the objective quality of Power Potential (Apparent Coefficient of Restitution).

Yeah, I would like that too. I don't think the measurements for the 90 are correct. I know the K90 measurements are correct, and TWU has that .25 inches narrower 21 inches from the buttcap than the PS90. I haven't measure the PS90, but I've seen them and didn't notice any difference in headshape.
Thanks for your detailed reconstruction, corners. I was aware that the sweetzones of a racket are related to swingweight, but it is very instructive to see that you can explain the differences in the sweetzones between both rackets down to a T from their differences in swingweight. In other words, headsize indeed plays a negligible role in the size of the sweetzones.

The big question for me, then, is: where does the proverbial difference in 'forgiveness' between 90 and 95 sq in rackets come from??

If a 90 will have the same sized sweetzones as a 95 of the same swingweight, the only remaining factors I can think of
that could contribute to this difference in forgiveness are:
  • Effective width of the stringbed (TWUs 'spinwindow'), which is a function of the actual width of the stringbed, frame thickness and impact angle. This would determine the risk of 'framing' or 'shanking' the ball, especially in a topspin shot
  • Length of the main strings, this would affect the amount of 'resilience' of the stringbed as in how much it contributes to shotspeed. But it seems to me that this factor could easily be compensated for by lowering the stringbed tension in a 90 frame

I think the general consesus among playtesters, not just on this board, is that a 90 is less forgiving than a 95 (hence the desire for a PS95 that plays like a PS90...). Is this difference, then, attributable to only a difference in effective width of the stringbed? Even when you compare the PS95 with the K90, TWU lists spinwindows of 5.50 in for the PS95 and 5.45 in for the K90 (location withs of 9.13 in and 8.98 in, respectively). That's a difference of less than 1%! So you'd have a 1% higher risk of shanking with the K90 as compared to the PS95...

So what's going on here? Is the perceived difference in forgiveness between a 90 and a 95 mostly subjective? Is it because we know that the 90 has a smaller stringbed that we convince ourselves that it must be less forgiving? Is it because 90s tend to be more hefty than 95s (certainly not always true, I play with the 4D200T myself!)? What am I missing in my list above? Can you enlighten me on this one as well, corners?
RF97, stock, full bed BHBR16 or TB16 @ 18x16 kg
Still in bag 2 x Dunlop 4D200 Tour, tailweighted to ~10 pts HL, 374g
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