【The Geometry of GOLF】 7. Shaft frequency and Stature (body height)
Head speed is the standard when choosing the stiffness of the shaft. Is this correct? The hardness of the shaft is measured by the frequency when the head is attached. It is obvious that the frequency is not related to the impact head speed, but the angular velocity at which the shaft rotates. Angular velocity is the number of rotations of an angle per unit time. The radius of gyration has nothing to do with angular velocity. However, the larger the radius of gyration, the faster the velocity of motion on the circumference of rotation, but if the angular velocities are the same, the frequency of the shaft is the same. The speed of motion on the circumference corresponds to the head speed. Certainly, if the turning radius is the same, the faster the head speed, the higher the angular velocity. However, even if the head speed is the same, the angular velocity increases as the radius of gyration decreases. Considering that the radius of gyration of the club is proportional to the stature, even if the head speed is the same, the shorter the stature, the higher the angular velocity, so the frequency increases and the stiffer shaft is suitable. For a 45-inch driver, R is about 240 cpm (frequency per minute) and X is about 280 cpm. X is about 1.17 times the frequency of R. Considering that the radius of gyration is proportional to the stature, the angular velocity is inversely proportional to the stature, so the angular velocity of a golfer with a stature of 160 cm is about 1.19 times that of 190 cm. In other words, even with the same head speed, if a golfer with a stature of 190 cm fits the R shaft, the X shaft will fit at a stature of 160 cm. In reality, the length of the club shaft is not that different, so it may not be that much. However, it is obvious that the size of the arc of the club trajectory differs depending on the stature. Therefore, it seems strange to determine the stiffness of the shaft (the frequency of the club) based only on the head speed. In fact, I’ve heard that short stature and fast head speed players, such as Massy Kuramoto and Ian Woosnam, used shafts that were even harder than regular X shafts and had very high frequencies.