Significantly increasing the sweet spot of the racket without adding weight, to make it easier to hit the ball with the racket.
Tennis rackets were initially made of wood (ash tree, maple, cherry, bamboo, etc.), and later of steel and aluminum alloys, but in 1974 the first CFRP racket made of carbon fiber was released in the U.S. In Japan, Kawasaki Racket released the "Ambitious" comprising a wooden frame with TORAYCA® cured plate attached to it in 1975, and in 1976 the company introduced the first-ever 100% carbon racket called the "Ruler." Japanese manufacturers developed and released CFRP rackets one after another. CFRP rackets had such features as fast ball, good durability and high design adaptability, but they were expensive and also their light weight, which is the greatest advantage of the CFRP racket, did not benefit the users much and therefore CFRP rackets did not sell well.
In 1976, however, the U.S. manufacturer Prince introduced an oversized racket having a larger sweet spot and racket face, by making the most of CFRP's "light weight and high strength," and since the stylish racket proved the greater design flexibility of CFRP, the use of CFRP for tennis rackets increased dramatically. The so-called "Dekarake" oversized racket that fully utilized the features of CFRP had a large racket face of 110 in2 at the same weight, compared to the mainstream racket face of 70 in2. It became a much talked-about racket having a significantly larger sweet spot and offering greater ease of hitting the ball.
Thereafter, rackets whose frame was almost as twice as thick as that of a conventional racket and also more rigid, were introduced, and since the higher (harder) frame rigidity reduced the flexing after impact and allowed extra energy to be transmitted to the ball, the ball bounced stronger. Utilization of CFRP made this performance improvement possible without making the rackets heavier than before.