Originally Posted by travlerajm
The pressure on the stringbed is only lessened in the normal direction (assuming that the racquet has the same stiffness in the plane of the stringbed).
But this touches on an important point - the bending stiffness of racquets varies not only the plane perpendicular to the stringbed, but also in the plane of the stringbed.
Racquets that are stiffenend in the plane of the stringbed tend to be more spin-friendly than you might expect. Examples include the AeroPro Drive, the Prince More Technology frames (like NXG), the Prince O-ports frames, and some of the higher end Wilson's (like K6.1 95, which is highly reinforced in that plane in the throat).
The most spin friendly frames (not accounting for string pattern) are those where the ratio of bending stiffness in the plane of the stringbed to the bending stiffness in the plane perpendicular to the stringbed is very high.
I did my own careful experimentation on this subject 8 years ago, when I first discovered how much differences in stiffness could affect spin.
I demo'd about 20 different racquets of various designs (several at a time) to collect data. I then clamped the handle rigidly to my kitchen countertop, and suspended a 2kg weight from the center of the stringbed (I used a full half-gallon plastic orange juice container with a loop handle).
I measured the distance in mm that the tip of the racquet would deflect due to the suspended weight. Then I rotated the grip 90 degrees, and measured the same deflection in the other plane too. The 2kg weight was selected so that the deflections would approximately match up with Wilson's old si index scale - 2-3mm deflection for a Wilson Profile in the plane perpendicular to the stringbed.
The stiffness highest ratio I measured was for the K6.195 16x18. Not coincidently, this frame had the highest TW review rating for spin of any racquet tested at that time. The AeroPro drive was quite stiff in the plane of the stringbed, but since it was also stiff in the perpendicular plane, it's ratio was not as high as for the K6.195. The Wilson Profile had the lowest ratio of any frame I tested (not surprisingly, with 38mm beam). The Profile is by far the least spin-friendly frame I've ever used.
The bottom line is that for maximum spin, you want a thin-beam frame that is highly reinforced in the plane of the stringbed. These types of frames generally work best with tight string patterns to compensate for the extra spin potential from the stiffness ratio. On the other hand, frames with low stiffness ratios (really wide beams) will tend to require open patterns (or spin-friendly string setups) to compensate for the lack of inherent spin potential.
Interesting theory, but even without questioning methodology there is clearly a problem:
stiffness of a racket is not tested in stringbed plane, it is tested in normal to stringbed plane ONLY.
From your examples - Super spiny K 6.1 95 has flex rating of 69!
From your earlier comments one would draw conclusion that because k 6.1 95 is stiff, then therefore it is not as spin friendly as something similar specs but softer, for example Yonex RQiS 1 Tour, which is btw has quite low rebound angle (and I assume spin)