RA — sometimes written as the Rahmen or flex figure — is how much a racquet frame deflects under a standard load, measured with the frame unstrung and clamped at the handle. A higher number means a stiffer frame.
In our catalogue the figure runs from RA 55 to RA 72, with the average at 65. So a frame described as "stiff" in a shop is usually about seven points above the middle of the market, not in a category of its own, and a frame at 60 is genuinely soft rather than merely softer.
What a higher RA does: it returns more of the ball's energy, so the frame gives more free depth for the same swing; it holds its shape better on off-centre contact; and it passes more of the impact shock into the hand, wrist and elbow. What a lower RA does is the mirror of all three.
What RA does not tell you: how the frame feels. Feel comes from where the frame bends as much as how much — two frames at RA 63 can feel completely different if one flexes in the throat and the other in the head. It also says nothing about the string bed, which is what your arm actually meets, and nothing about swing weight, which decides how heavy the frame feels in motion.
We calculate the comfort criterion on every racquet page directly from RA, because it is the one honest input we have for it. Where a frame carries no RA figure in our records, that page shows no comfort score at all rather than an estimate.