Tennis Racket String Tension

String theory

Choosing a tennis racket takes a certain amount of knowledge, and what a lot of people don't know is that a racket's stringing may be more important than its frame. There are tradeoffs between power and control in relation to string tension, and any racket worth its salt will have a recommended range of tensions - 58 to 68 pounds, for example. Within any given recommended range of tension, a low tension offers more power and less impact on the arm, while a high tension offers more control and better spin.

To understand why low tension allows greater power, it helps to compare the energy return offered by the strings to that offered by the ball. The official rules of the game dictate that if the ball is dropped on concrete from 100 inches, it has to rebound to between 53 and 58 inches. In a collision of any kind, energy is lost to vibration and friction; with a tennis ball, a large amount is lost when the ball compresses. The rubber stores that energy, releasing it when the ball decompresses. If the lost energy were stored with perfect efficiency, the ball would bounce back to 100 inches, but a tennis ball dissipates about 45 percent of that energy.

Strings, on the other hand, dissipate only 10 percent of impact energy. The more the strings store energy in a collision, the less the ball will store energy by flattening. For the greatest return, the strings need to store as much of the total energy as possible, as they will return over 90 percent of it. By contrast, almost half of the energy a ball stores is wasted. Looser strings deform more easily and store more collision energy, but at the unfortunate cost of control.