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Tennis Tech - Racquet Science

Unfortunately, "tennis science" in the last couple of decades has become increasingly marketing driven. The true science of racquet performance is often buried in a haze of marketing superlatives and visual interpretations that have no connection to what's actually happening. If racquets are truly high-tech, then we should rely on performance science and less on marketing science.


BOLT believes that access to objective technical analysis is critical to enable modern athletes to make sound choices about equipment use. We hope this can lead to a more competitive market, longer term thinking about innovation, generally better products for athletes, and an improved tennis experience.

MYTHS of Tennis Technology - Top Four

1. "Pulley Action" on the string-bed is viable and is a good thing for a racquet.


No. This concept has been embraced in numerous designs over a few decades as a way of "activating" the string-bed. It's relative ease of execution has led to a number of products. The MITT "Rocker" and the Wilson "Rollers" racquet are the best examples that we're aware of. Anyone that has tried either one will understand that the string-bed movement offers some "softness", but the response of the string-bed generally is extremely unpredictable and very inconsistent. Its been proven time and again that the pulley model does not deliver a predictable response. This makes sense because it can't.


The theoretical pulley model, which assumes that the strings can move freely, is illustrated here. The red arrows indicate typical movement of the strings at ball impact. Both views clearly show that a ball is acted upon by multiple strings. Unfortunately, in the pulley model, every other string is counteracting the one next to it. A string moving in one direction is directly adjacent to a string that's moving in the opposite direction. It's not difficult to understand how this disrupts the equilibrium of the string-bed generally with each string resisting the one next to it.


The second question, and maybe the most important, is how far a string can actually slide across the other strings unless moved by direct ball impact. Anyone with even a little tennis experience will know that strings don't slide across one another easily. Certainly, once the strings are notched at the intersections, they are not moving anywhere! This condition likely further exacerbates the inherent unpredictability of this design model. 

"Pulley action" plan illustration
"Pulley action" isometric illustration

"Pulley Action"

Zipstrip "piston action" plan illustration
Zipstrip "piston action" isometric illustration

"Piston Action" - ZIPSTRIP

"Pulley Action" has been relied upon over the years because of its relative ease of execution but it's always been an inferior option compared to the ideal theoretical model as demonstrated by "Piston Action". Due to technical limitations, Piston Action has never been truly achievable to a degree that can be used on high-performance equipment, until now!

The BOLT ZIPSTRIP offers pure, true Piston Action, exactly as spring suspension was always meant to be. As the red arrows indicate, the movement and forgiveness of the string-bed is entirely uniform. The strings are all working together in unison at ball impact. It makes the response of the string-bed very predictable and with very consistent feel.

2. Polyester mono-filament string is good for "string breaker" players.


It may seem to be the right choice for big hitters because it doesn't break as easily as multi-filament or synthetic string, but if performance is a concern, then it may be the wrong choice. Unlike other strings which can remain elastic and playable for months, polyester mono-filament does not. Poly has a yield point like steel. Once the yield point is reached, the material is never coming back to "elastic performance". At this point the stringing is "dead". Research indicates that this can happen very quickly, even in a matter of days, and even without use. There is some further evidence that "creep" occurs wherein the static tension in the string breaks down the molecular structure of the polyester over time while at rest.

3. It's possible to have control and power together on a conventional racquet.


No, conventional racquet dynamics do not allow for power and control to each be optimized on the same racquet. It's a simple reality of physics that the frame cannot perform two inherently opposite tasks at the same time. In order to have control and power optimized and together in harmony on racquets, there must be one component to handle power, and at least a second component, to handle control. 

4. Sacrificing the structural integrity of the racquet frame in order to achieve control of ball-rebound speed is a good thing.


No. In most typical engineering applications, sacrificing the structural integrity of the components would be a bad design model. Until now, it's the only model that's been fully embraced in racquet design. New materials and manufacturing techniques make it possible to discard this outdated model and embrace a more serious paradigm for racquet design. 

Chart showing Young's Modulus
Image of steel bar elongation and rupture
Brief Timeline of Racquet Design
Tennis Tech - GLOSSARY

Compression - energy absorbing phase of spring deformation under loading.

Creep - process of molecular structure breakdown that can occur with a material under tensile stress over a period of time.

Dwell time - length of time the ball stays in contact with strings; depends upon a number of factors including string type and tension, string length, swing speed.

Dynamic Sweet Spot - in the case of a BOLT racquet with spring suspension, the sweet spot actually expands at ball impact - it responds "dynamically"; the physical reaction is that increased tension from ball impact is lowered, thereby extending the effective length of the strings to expand the sweet spot area. 

Impact shock - first high-amplitude "pop" of the ball impacting the strings; known to be one of the most harmful effects to players of striking a tennis ball; not to be confused with vibration.

Polyester mono-filament string - a single strand of spun molten plastic; responsible for massive increase in ball spin generation; inelastic/stiff - causes ball to compress on strings; for fast swing speeds: advanced players; impact shock is significantly greater than multi-filaments and synthetic guts.

Rebound speed - speed of ball releasing from strings.


Snap-back - describes a lateral bending and sliding of the strings across one another and the subsequent transfer of spin energy to the ball as the strings "snap back" into place in their static position at rest.

Spring-back - return energy phase of spring compression as spring returns back to static position at rest.

Suspension (system) - (mechanical engineering definition as applied in automobiles) an arrangement of springs and shock-absorbers connecting the wheel units to the chassis; in a racquet, the wheel units are the strings (they take the impact directly from the ball) and the frame is the chassis - ball impact forces are filtered from the strings through the suspension and then to the frame.

Sweet Spot - generally the string surface area of a racquet which generates optimum hitting qualities such as maximum energy return, low vibration, etc; depends upon multiple factors including string type, length, tension, head shape, swing-weight, weight distribution, frame stiffness, etc.

Torque - twisting effect of ball impact forces on a frame.

Tech Driven Growth

It's safe to say that the design and performance of tennis equipment, and racquets in particular, have been the target of focus as both an art and a science since the earliest days of the game. A brief glance through etchings, drawings, photos and patents makes clear the depth of thought and creativity that have gone into the field over more than 100 years.

BOLT celebrates this rich history. We know that tennis players often develop "special" relationships with their racquets. It is a players' direct connection to the ball and the game itself and the most experienced players will invariably have a long list of very specific preferences including weight and balance, grip size, string tension and type, to name just a few.

It's this special relationship of player and racquet that has made technological breakthroughs in racquet design particularly impactful over the history of the game. A single significant shift in technological capacity has often fueled major leaps in interest and participation, as well as changes in the way the game is played.

We hope to provide a spark of innovation for tennis. We're committed to making the game easier to play, more comfortable, and more powerful than ever before.

Era of Polyester String

It is hard to deny that the most significant change in tennis equipment in the last 20 years or so is the rise of polyester mono-filament string. Having taken root at the tour level, polyester string has flourished, whether for good or bad, to influence the game at all levels of play.

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Tennis Tech - LINKS

BOLT - BOLT Sports website -

  • Demo and purchase racquets and equipment.


BB Studio - Brett Bothwell Design Studio

  • BOLT Design Engineer website.


ITF - International Tennis Federation

  • Global tennis' governing organization.


TWU - Tennis Warehouse University

  • Excellent resource for tennis tech info of any kind. Incredible database of equipment testing and analysis' - built by two great researchers, Crawford Lindsey and Rod Cross.


USRSA - US Racquet Stringers Association

  • Solid resource for tennis equipment info.

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