As in other sports, rule and equipment changes have periodically modified how tennis is played. Fifty years ago, Diogenes first used a 65 square inch wooden racquet with strings made from sheep’s guts and used it to strike white balls. The professional tours adopted yellow balls in 1972 because they provided more contrast and were easier to see on color televisions. Over the next several years, yellow balls were adopted by most recreational players. In the late 1970s, the game migrated to graphite racquets with about 100 square inch heads, allowing players to hit much harder with greater spin and consistency.
By the 1980s, nylon strings replaced natural gut strings for most recreational players. They were less expensive and not as sensitive to moisture degradation as gut. Co-polyester strings were widely adopted by professionals in the early 2000s, although nylon is still used by most recreational players. Polyester strings are very stiff and have very little elasticity. This is what makes them popular with big hitters. Because of this lack of elasticity, the ball doesn’t trampoline off the stringbed, so a player can take a big swing at the ball without it sailing long. The stiff string also digs into the ball generating more spin as the strings brush across the ball. Most recreational players find that this stiffness requires taking bigger swings at the ball or the resulting shot lands short in the court, which is a weak shot. Not only do they have to work harder, but the string’s stiffness results in more shock transfer to the player which can result in shoulder, wrist or elbow injuries.
The search for increased control by using more spin has been a constant quest by string and racquet companies for years. Tennis researcher John Yandell analyzed slow-motion video and determined that current world #1 Rafael Nadal hits his average forehand with 3200 rotations per minute (rpm) and sometimes reaches a mind-boggling 4900 rpm. By comparison, Roger Federer’s forehand averages 2700. And Pete Sampras and Andre Agassi, two of the America’s greatest players ever, hit their forehands at a mere 1800 rpm, imparting slightly more than half as much spin as Nadal. When we talk about spin, mostly we are referring to topspin. Although underspin (slice) is a solid occasional play, chipping the ball is as often as not a defensive stroke. This is so because of the trajectories of balls struck with topspin versus one struck without spin, as shown in the chart below.
A flat tennis ball has a lower margin of error to both clear the net and land inside the baseline. A ball hit with more topspin will travel higher over the net and bounce higher, making it more difficult for the opponent to hit. (This is so because most strokes should be hit at a height between the player’s knees and below the chest in order to create a low-to-high loop. When the ball bounces above the shoulder, a player can choose to hit a weaker, higher shot, or retreat in the court in order to create the proper contact height.) In the past, the combination of smaller head size, lower powered racquets and lower technology strings prevented players from being able to easily access spin.
Dr. Rod Cross, co-author of The Physics and Technology of Tennis, demonstrated through lab research that as a ball is about to leave the strings, the main strings snap back and give the ball a sideways kick, thereby increasing the rate at which the ball spins as it comes off the strings. In other words, about 80% of the spin, and control of a ball is determined by the mains, or vertical strings in the racquet. A looser pattern imparts more spin, but lower control. In the past, players chose between tight string patterns such as 18 mains X 20 crosses in order to maximize control, or looser string patterns such as 16 mains X 18 crosses to increase power. These trade-offs could be somewhat mitigated by other variables such as string tension (looser for power; tighter for more control), string type, frame size, beam width and racquet weight. As a DIY racquet stringer, Diogenes has considered what enhancements could boost effectiveness. The holy grail would be to retain control while increasing spin or power. Other stringers had suggested to Diogenes that one could achieve that end by either skipping the first and last crosses, or skipping every fourth cross. The results from these experiments were not good.
In early 2013, Wilson put out the Steam 99S, a racquet that had a 16 X 16 string pattern. Intended for intermediate players, the results were too powerful for Diogenes. Prince jumped on the idea, and about a month ago introduced several racquets with fewer cross strings. Two weeks ago, Wilson introduced the Prostaff 6.1 95S, with an 18 X 16 string pattern geared towards more advanced players. “For every 100 r.p.m.’s of topspin you can put on the ball, you can reduce the flight distance by 6 to 12 inches,” Bob Thurman, Wilson VP for R&D said. The goal, is to reduce the coefficient of friction between the strings and allow them to move more, which creates more force when they snap back. In other words, to create more spin without a change in one’s swing. Wilson has attempted to solve this problem for control players by creating a racquet with fewer cross strings than vertical main strings.
A few days ago, for the first time, Diogenes purchased a racquet without first demoing it. The new PS 95S has the potential to radically improve his mediocre strokes without making changes in how he strikes the ball. Many iterations of stringing may be required to achieve that result, but that is part of the fun of a winter indoor season. Testing and adjusting to new equipment is a routine practice from the pro tour down to lesser players. Sometimes it works, and sometimes not, but the pleasure is in the process of finding things out. Ain’t life just grand?