• Brett Bothwell

Engineering Control In Racquet Design

What is control in a tennis racquet? How is the term control used in racquet marketing dialogue? Is it the same as actual performance? It makes sense to think a reference to control in racquet performance indicates a harnessing of all aspects of ball flight. Control of ball speed, direction, trajectory and spin would all seem to be covered by a general reference to control in racquet marketing materials, but that's not the case.


In the current era of carbon composites and custom mold making, racquets can be made in many different weights and balances, and there are nearly endless possibilities of head shape, profile contours and throat designs. As a way to simplify the racquet selection process and to make possible the introduction of multiple variations of racquets, tennis marketers have stripped away technical details. While there's merit to this approach in terms of sales, the engineering behind racquet design gets diluted and the dialogue, or the implications of the dialogue, are not technically accurate. Lack of scientific explanation behind racquet design isn't deceit or disingenuous marketing, it's well intended, but it can lead to genuine misconceptions about how a racquet performs, what's actually possible and about how performance in a racquet is achieved.


In the context of marketing and racquet selection jargon, the term control refers directly to control of ball rebound speed. Control alone is not a reference to directional control to gain precision or accuracy, and it's not a direct reference to spin or trajectory. The term control in tennis racquet lingo describes the ball impact energy a frame absorbs. Control on its own then becomes a simple way to distinguish one frame from another, without diving into the complexities.


Currently, racquets are divided into two basic categories: control racquets and power racquets. A stiff racquet frame absorbs very little ball-impact energy and is generally a power racquet. A flexible frame can absorb a great deal of ball-impact energy and is generally a less powerful racquet - a control frame. Ball-impact energy absorption in a racquet frame—stiff v. flexible—is the heart of the standard racquet selection model of the modern age.


Often, the selection model doesn't align precisely with actual performance. Left out of selection marketing dialogue are the residual effects of making a racquet flexible or stiff. Some trade-offs in comparisons between the two are left unsaid. The most blatant trade-off regards the flexible frame. The more flexible a frame, the less stable it becomes. A flexible frame potentially is less able to maintain directional control of ball flight in a player's hand than a stiff power frame. Designers (and users) of flexible racquets can make a valid claim about controlling ball rebound speed and providing comfort, but making a claim to control ball flight for precision and accuracy is a stretch. Another serious trade-off in performance of the flexible frame is a loss of power. A flexible frame absorbs ball impact energy to reduce ball rebound speed. The more flexible and comfortable a frame is made, the less powerful it becomes. In the context of conventional racquet design, there is no way around this predicament.

Most people who have purchased a high-performance tennis racquet are familiar with the racquet buyer's dilemma. The central element of the dilemma is that buyers must choose between power or control. Selecting a racquet is a process of determining which performance trade-off a player is willing to make. Sacrifice control (and comfort) for power? Sacrifice power for control (and comfort)? The selection process—racquet buyer's dilemma—implies compromise: The sense that an element key to performance must be given up.


The racquet buyer's dilemma is the logical result of conventional racquet mechanics. The way conventional racquets are fabricated, whether the frame is flexible or stiff, how they respond to ball-impact energy determines levels of power, ball rebound speed and comfort. Power, rebound and comfort are qualities compromised to various degrees to enhance the performance of one quality over another. The result is an inherent problem in frame design that alters performance: The frame, apart from the strings, must do everything. Call it the sticks-with-strings approach. Relying solely on the frame (stick) and how the strings are strung into a frame becomes the reason control, comfort and power cannot be optimized in one racquet. A frame cannot respond in two different ways at the same time, i.e., it's technically impossible for a frame to be flexible and stiff. It may be possible to make segments of a frame stiff, while other parts of a frame are made flexible, but the segments are merely parts of the whole—the sum of the segments do not add up to a whole high-performance frame that encompasses all the qualities necessary for prime performance. The fundamental characteristic of a tennis racquet, determined by shape, materials and simple physics is that a frame is flexible or less flexible, stiff or less stiff.


It's the inability of a tennis racquet frame to do two different things at once at the root of the fundamental limitation in the design model of conventional racquets. It's not that the model is broken, it's that the model has hit a ceiling. In the current era of power tennis, bigger, stronger, faster athletes collude with new technology to push the limits of the game and themselves. But current frame design models are maxed out. A professional athlete must have some degree of flexibility in a racquet frame to control ball rebound speed and keep the ball in the court. Many professionals may require some flexibility in a frame for comfort as well. If the frame is too flexible, too much power will be lost and, more importantly, the frame can lose its ability to control ball flight. Some high-performance athletes may find themselves facing the same racquet buyer's dilemma recreational players face, with far more at stake and no good options to achieve an optimum balance between power and control.


A majority of recreational players value power over control, a stiff racquet over a flexible one. Amateurs want to play like pros but typically do not possess the strength required to hit like a pro. A stiff power racquet can make up the difference in force, but stiff racquets provide less comfort and are harder on the body. Because stiff racquets don't absorb ball-impact energy, the players' bodies must. A recreational player with the stiffest racquet often has the least physical strength and is most in need of comfort and relief from ball-impact energy. Whether a pro athlete or a club player, the breakdown in tennis racquet frame design is the same for each, with the same effects. There is no good way to provide relief and minimize injury potential without making the frame flexible. How flexible can a frame be before it's not powerful enough? The solution is not a solution but a compromise between the qualities of power, control and comfort, where none is optimized.

In a conventional racquet, the frame and strings combine to produce overall racquet performance. Nothing more, nothing less: Frame + Strings = Performance. That same model has been used for racquets since the beginning of tennis, more than a hundred years ago. Frame plus strings is the racquet model used to develop countless designs in wood, steel, aluminum and, now, carbon fiber composites. Even though carbon composites are many times stronger and lighter than previous materials, and they enable superior performance dynamics, carbon composites are still utilized in the framework of an outdated and relatively primitive engineering approach.


Instead of re-thinking the existing model to best utilize new high-tech materials, with a structural capacity never before seen in the history of racquets, composites are being modified to mimic previous racquet materials, including wood, maintaining the century-old sticks-with-strings approach. The latest oldest designs are the new super-flex racquets. Super-flex racquets are carbon composites designed to play like wood racquets. And they do. The racquets are so flexible they only can control ball-rebound speed, sacrificing direction and trajectory. Does tennis need to reach this far back in its past for a solution to power and control? No, but the industry does need to take a look back at the evolution of suspension engineering.


Suspension is a basic engineering paradigm employed to address impact force management in a myriad of applications, from cars to planes. And it can be practically applied to address the ball-impact energy dilemma faced in modern racquet design. Not too long after we humans discovered fire, we invented the wheel. Then we figured out that by attaching wheels to various objects we could easily roll them across the ground. Rudimentary wagons followed. We made a box, connected wheels with an axle, attached the axle to the bottom of the box, added a handle for pulling. The wagons-with-wheels design model was born: Wagon + Wheels = Performance. But there was an early design flaw. Anyone who owned a Radio Flyer or similar red wagon might remember that if it was pulled too fast when filled with stuff and hit a bump, everything in it flew out. As wagons evolved to go farther and faster and carry people and anything else that needed moving from one place to another, suspension mechanisms were added between the bottom of the wagon and the wheel-and-axle assemblies to cushion the ride and keep everyone and everything from flying out. Necessity is, indeed, the mother of invention.


As engines replaced horses and travel became faster and the distances covered much longer, suspension mechanisms were critical in making transportation safe and comfortable. The power and speed allowed by technological evolution required the adaptation of a new design model so transportation could continue to evolve and remain safe and comfortable. In today's highly evolved transportation industry, with extraordinary power sources capable of creating tremendous speed and generating ever-increasing impact energies, suspension engineering is indispensable to make it all work. The modern transportation design model evolved from: Wagon + Wheels = Performance to Wagon + Suspension + Wheels = Performance.

Tennis racquet design is poised to follow a similar evolutionary arc as the wheel to enhance performance and optimize power, control and comfort, from: Frame + Strings = Performance to Frame + Suspension + Strings = Performance. It's logical. It's simple. It's time has come. In fact, string suspension has arrived on a high-performance racquet in the form of a Zipstrip, a patented string-suspension model available from BOLT. And only from BOLT.


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