A primary source for understanding the fundamental aspects of golf is still the superlative study, titled Search for the Perfect Swing, by Cochran and Stobbs ([1968] 1999). This study, which started in the 1960s and involved the collaboration of academics from a number of research institutions in Britain, resulted in a wealth of information that, 50 years on, still forms a solid foundation for the scientific study of the game. The title of the present work is intended, in part, to pay tribute to many of the explanations in Cochran and Stobbs, which were made before the existence of invaluable experimental data from wind-tunnel testing, ultra high-speed photography, laser monitoring, and Doppler radar tracking systems. However, the title has more to do with the performance of PGA and LPGA Tour players, which has been captured by the Trackman Company, and which over the aggregate represent as near to perfect golf as it is possible to measure. The overall goal of this text has been to lay down, as well as possible, the science necessary to describe the ball striking of this group of elite players, and at the same time to try to establish some measure of the improvement in performance of golf equipment in recent time, particularly for the modern titanium driver and the current generation of premium golf balls.
Since the time of the “perfect swing” study, according to Thomas (Just Hit It, 2008), the Technical Director of the USGA from 1974 to 2000, only three equipment innovations have made a profound change to the game of golf. These are perimeter weighting of club heads, the graphite shaft, and the incorporation of spring effect into the face of hollow titanium drivers. To this list should be added the latest premium golf balls, designed to perform quite differently with the driver and the grooved irons. But even this can be attributed to the thin-face titanium driver, which from the necessity of surviving multiple impacts could not have a grooved face.
The use of perimeter weighting, producing a “cavity back,” increases the “moment of inertia” of the club head, and so reduces club head rotation for off-center hits. This was first established in a putter in 1966 by Karsten Manufacturing Company. Named the “Anser” putter, it became the most successful putter ever both in terms of sales and tournaments won. By the 1980s, the inventor, Karsten Solheim, had introduced an even more significant innovation by using investment casting to create cavity-back irons using the trade name “Ping.” According to Thomas (2011), the second generation of cavity-back irons, the Ping Eye2, was used by Bob Tway in winning the 1986 PGA Tournament. Now investment cast cavity-back irons are used by almost all amateur players. The original forged “blade” irons, with the weight concentration at the sole, are still used by a majority of professionals and highly skilled amateur players. The reason typically advanced for this is that the blade irons have better “feel” and provide better ball flight control. However, it seems much more likely that these clubs are more suited for the downward angle of attack on the ball and the resulting extra compression of the ball between the club face and the inertial resistance of the ground.
Investment casting is just the modern term for the lost-wax process, with automation applied for low-cost manufacture. It allows parts to be cast with a very high level of precision, including the very smallest features. This allowed Ping to cast U-shaped grooves into their irons, which eventually brought the Ping development in grooves to the attention of the USGA. As mentioned previously, golf balls need to grip the face for the high-spin generation, and they do this much better with U grooves than the V grooves traditionally machined into forged irons. The main issue became that if the U grooves are large enough with a very small profile radius at the top edges, then the club face could grip the ball enough in deep rough to still spin the ball well. This threatened to remove much of the penalty from errant approach shots, which finally resulted in the USGA fighting a multimillion-dollar lawsuit against the Ping Corporation. One of the best lines in golf literature is in Just Hit It (2008) by Frank Thomas in which he writes, “I came to think of Karsten (Solheim, Founder of Ping) as a friend, even though he sued me personally for $100 million.”
It was only a matter of time before investment casting would be used to create hollow drivers with the greatly increased moment of inertia. The first successful introduction of this driver design, using investment cast stainless steel, was by the Callaway Golf Company in the late 1980s. This led them to dominate the golf club market for 10 years. By 1995 they had gone from $5 million to $500 million in sales. At this point, they introduced the Big Bertha, investment cast using high-strength titanium alloy to produce even larger driver heads with the consequently greater moment of inertia. The high strength-to-weight ratio of the titanium alloy was accompanied by the unparalleled lightweight spring quality of the material. This produced additional performance improvements, which will be discussed following a brief diversion.
torque, it spins at only one-quarter of the speed; that is, the radius doubled makes the resistance to rotation increase by 2 squared or 4.
So the reason for making driver heads large is to move the 0.44-pound typical head weight as far away from the center of the club head as possible. The torque produced by off-center ball strikes then rotates the head backward less and so projects the ball forward more. The same applies to off-center strikes with irons and putters where perimeter weighting has pushed the mass outward from the center, thus increasing the MoI.