Spin Doctors

Racket technology saved tennis, and Roger Federer is proof

Roger Federer should not exist. The twenty-four-year-old from Basel, Switzerland, has won three consecutive Wimbledon championships and dozens more titles, both major and minor, while rarely losing a match over the last three years. It’s not the pace of his victories, however, that makes Federer such a marvel; it’s how he wins—with perfectly placed serves, a devastating forehand, a flowing one-handed backhand, timely volleys, and feet as nimble as any the game has known. He’s the sort of versatile player that the modern power game supposedly had snuffed out for good.

Fifteen years ago, a champion as sublime as Federer was unthinkable. With men like Pete Sampras, Richard Krajicek, and the six-foot-four-inch Goran Ivanisevic acing their opponents into submission, it seemed that the last days of tennis were near. Top players were becoming bigger, rackets more powerful, and, as the aces piled up, matches would become monotonous and the sport would die, one 150-mph serve at a time. There was no longer a place at the top for men in the mold of Rod Laver and John McEnroe. Pundits were calling for the elimination of the second serve, an increase in the height of the net, and even a return to the wooden racket.

Today tennis balls zip across the court at sharper angles. Rallies are not too long, as many complained in the days of Ivan Lendl and Mats Wilander, but not too short, either, as in the 1960s and 1970s, when serve-and-volley pervaded the sport. The mean speed of the game’s fastest serves is higher—138 mph at Wimbledon last year, up from 132 mph in 2002, according to the International Tennis Federation—but return of serve has improved too, as evidenced by a flat trend for tiebreaks and aces at Grand Slam events since 1998. On the lawns of Wimbledon, widely considered the sport’s fastest surface, the percentage of sets ending in tiebreaks—the more tiebreaks, the more servers can be said to be dominating the game—has remained around 16 percent since 2002, down from the 21 percent peak in 1989.

Ruling over this fast-paced and exhilarating brand of tennis is Federer. His tennis is art, a triumph of variety and precision over power that inspires awe among rivals and onlookers alike. “He’s the best I’ve ever played against,” Andre Agassi said after losing last year’s U.S. Open final (Federer’s second straight Open victory). For younger players, though, it’s not so much awe as the flattery of imitation. “I love the way it’s going,” said Brad Gilbert, a former pro who has coached Agassi and Andy Roddick. “In the 1980s people were saying the game was going to become comical. But the juniors now, they are doing more. They watch Federer.”

The tale of what tennis did not become begins with the racket, perhaps the most misunderstood implement in the history of sports. The composite, or “graphite,” racket, made from carbon fibers and other materials including Kevlar, took over the game in the 1980s. Composite rackets are routinely cited as the villain behind the surge in power in tennis, yet it is these rackets that saved the game from becoming an utterly boring one. The fact is that composite rackets help players hit better ground strokes, impart more spin, and return rocket serves, but they do very little to speed up serves. In 1997, in a comparative test done by Tennis magazine, Mark Philippoussis, the six-foot-five, 217-pound Australian renowned for his powerful serve, averaged 124 mph when serving with his own composite racket. With a classic wooden racket, he averaged 122 mph.

Scientists explain this using a simple formula: ball velocity after impact divided by ball velocity before impact (the racket must be suspended freely or held firmly in hand, not clamped in place). The resulting number, called ACOR, for Apparent Coefficient of Restitution, is an indicator of how much energy a racket loses when it collides with a ball. If a ball approaches a racket at 100 mph and bounces off it at 40 mph, the ACOR is 0.4. A racket with a higher ACOR is a racket with more power. Crawford Lindsey, a partner at the United States Racquet Stringers Association and co-author of the influential Physics and Technology of Tennis, points out that wooden rackets, because of their greater weight, have a greater ACOR than most of the composite rackets on the market today (though only when struck dead center). Top players serve so much faster today not because of their rackets but because of their raw physical power. Male professional tennis players have grown roughly two or three inches taller and fifteen to twenty pounds heavier in the last thirty-five years, according to International Tennis Federation data.

While the racket does not impart speed to the serve, it has a lot to do with the accuracy and pace of forehands and backhands. Stiff carbon fibers produce a structurally sound racket at a lighter weight than wood—as little as nine ounces compared with fourteen or fifteen. Additional weight placed along the head, away from the handle, improves stability and prevents the racket from twisting or bending backward upon impact. As a result, the racket returns more energy to the incoming ball. It also has more power—a greater ACOR—for off-center hits. Put simply, it has a larger “sweet spot.”

For pros, however, the single most important feature of the composite racket is its wider face: usually around ten inches compared with the eight- or nine-inch wooden rackets wielded by the likes of Tilden, Budge, and Laver. To create significant topspin, a player must tilt the racket forward by two to five degrees and swing from low to high. The extra space provided by the composite racket constitutes a greater margin of error against unwanted contact between the ball and frame. It lets the player swing faster, which creates more pace and more spin, which keeps the ball inbounds despite the higher speeds. A low-to-high swing of similar speed with a narrow wooden racket would end in horrendous mishits. (A swing of similar speed along a flat plane would launch the ball out of bounds.) The extra width of composite rackets allows today’s bigger, stronger players to put more of their muscle into their strokes, yet maintain control because of the extra spin. “It’s not 10 percent more spin,” said Rod Cross, a professor at Sydney University and one of the co-authors of The Physics and Technology of Tennis. “It’s like 400 percent more. If a player wants to return a ball with topspin, he has to reverse the spin of the incoming ball. With a wooden racket, you were lucky if you could bring the spin of the incoming ball to a halt.”

Racket companies produce dozens of new products each year with advances in weight distribution, stiffness, and aerodynamics that aid amateurs, but none of it matters much to the best players in the world. For them, racket technology has remained more or less frozen since the 1980s, when composite frames gave them that all-important inch. Because pros do not lack for strength, they choose heavier rackets to provide more stability and control. Federer prefers a Wilson, just ninety square inches, that is very similar to the eighty-five-square-inch model Sampras used throughout his career. Among top professionals, only Agassi uses an “oversize” racket (in his case, 107 square inches). For most elite players, an oversize frame has no benefit over a midsize. The additional width (eleven inches compared to ten) allows the ball to travel farther along the string bed, but only if a player swings at a steep angle consistent with a topspin lob, not a ground-stroke drive.

Strings are the other technological variable in tennis rackets. It was once thought that stringing a racket tightly would increase power, while less tension would improve control. The opposite is actually true, though the differences are marginal: looser strings slightly increase power by turning the racket into a slingshot, while tighter strings add a bit of control by releasing the ball sooner, which lets players swing faster and brush up on the ball, creating topspin. Players routinely reinforce the myth that one type of string produces more spin than another. In the last four years, almost every top male has at some point switched from gut strings, made from cow intestines, to polyester strings—such as Luxilon—or to some combination of the two (usually polyester for the main strings, which travel from throat to tip, paired with gut on the cross strings, though Federer favors the opposite). Agassi, speaking to reporters recently, said Luxilon strings “really bite the ball,” increasing spin.

This view, however, is unfounded. “The roughness of strings, the pattern of strings, the gauge, and the materials—none of that stuff makes any noticeable difference for spin,” Lindsey said. “They probably are getting more spin, but it’s not for the reason they are saying.” Luxilon strings are stiffer than natural gut. This stiffness reduces ACOR ever so slightly, reducing power by 1 or 2 percent. Such a small decrease hardly registers on a radar gun, but it may shorten the maximum distance a ball travels by two or three feet. To compensate for that lost distance, Lindsey said, players swing harder, increasing pace and creating more spin. In essence, today’s men are responding unconsciously to less powerful string materials that, combined with larger head sizes, let them vary the speed and spin and sharpen the angles.

Taken together, this science makes sense of the sport’s evolution. Larger players of improved fitness have learned to push their rackets further—opening their stances, shortening their backswings, and swinging so forcefully that the energy they unleash lifts them off the ground. Federer and such players as Rafael Nadal, Marat Safin, and James Blake swing with such ferocity that they must use less powerful rackets in order to produce the spin and angles essential for attack. The rackets put brute force in the service of finesse. The players don’t serve-and-volley much, fearing a sharply angled, heavily spun reply. They do, however, charge the net as needed. They punish short returns. They hit dazzling—and once impossible—crosscourt winners from outside the doubles alley. The game is a lot more interesting to watch.

All of this happened with no drastic rule changes and little interference from the sport’s governing bodies. Just think if they had legislated a return to the wooden racket. The server would be striking the ball just as hard, but the returner, armed with a narrow racket that twists easily and can’t impart much topspin, would stand helplessly at the baseline. Instead of serve-and-volley, there would be serve. “The game has adapted to the circumstances we were afraid of,” Lindsey said, “and very quickly. Federer by himself is changing the whole game—back to an all-court game, only at a higher level. That’s how evolution happens.”