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Research and Development

New Design Model - New Priorities

The application of a suspension engineering model to racquets makes the possibilities for evolving and developing racquet performance into the future nearly limitless.

Instead of developing a multitude of flexible frames, the priority now moving forward is to develop a multitude of flexible, energy-absorbing suspensions. Degrees of energy-absorption and flexibility can be developed, and the ways in which suspension and flexibility are achieved can be developed too.

The path forward for racquet design is clear to BOLT. Massive impact forces present in modern day tennis ball collisions require more than just a stick with strings to mitigate. All the signs are here: numerous top players battling arm injuries consistently, numerous players citing "dead arm" as a reason for retirement, string tensions decreasing as a means of creating impact relief from polyester, and Ibuprofen and therapeutic arm-bands becoming a more integral part of the tennis community care regimen than ever before.


There is an incredible new era of racquet performance just waiting to be unleashed, and BOLT is committed to pushing it ahead for the benefit of all. The potential for improving the tennis playing experience is immense.

Massive impact forces present in modern day tennis ball collisions require more than just a stick with strings to mitigate.

BOLT racquet concept design

BOLT is a technology driven company and we're determined to keep reaching for the front edge of innovation in order to protect athletes, optimize equipment performance, grow the game, and to make every product better than the last.

The ZIPSTRIP is basically a plastic tube configured in a "cross-bow" shaped profile. It's advantage is its incredible strength, super light weight and simplicity. Depending upon the materials and the shape of the strip, it can be made to support very large string tension loads while still having some range of flexibility left over to respond to ball impact - and have the strength and flexibility to perform over and over for every shot for an extended period of time.


This is the challenge of spring suspension that racquet designers have pursued for 100 years and that BOLT has solved: How to achieve true spring suspension which is lightweight enough for the entire head frame, while still having the necessary strength capacity and range of flexibility leftover to perform at the highest levels over an extended period of time? The ZIPSTRIP. It's a huge milestone.



  • Develop flex response of plastic shell

  • Explore response of fill materials: rubber, silicone, gel, and gas

  • Develop profile shape

  • ​Calibrate flex/spring: firm - soft

  • Controlling dwell time: slow release - quick release

  • Degrees of comfort and feel

  • Methods of production - economy

Silicone injected Zipstrip selection

Playing Level:

Swing Speed:

Beginner to Intermediate

Slow: 0 - 20 mph

Zipstrip - Series X

Maximum Ball Pocketing

  • Max Dynamic Response Range

  • Max Forgiveness

  • Max Comfort

No Core
Series X

Playing Level:

Intermediate to Advanced

Swing Speed:

Med: 20 - 60 mph

Playing Level:

Advanced to Tour

Swing Speed:

Fast: 60 - above mph

Zipstrips - Series XS
Series XS

Quick Ball Release

  • Minimum Dynamic Response Range

  • Minimal Ball Pocketing

  • Enhanced Feel

Silicone Core

Slow: 0 - 20 mph

Beginner to Intermediate

Swing Speed:

Playing Level:

Playing Level:

Intermediate to Advanced

Swing Speed:

Med: 20 - 60 mph

Playing Level:

Advanced to Tour

Swing Speed:

Fast: 60 - above mph

Anchor 1
In a BOLT racquet, the frame is no longer the element responsible for control and comfort, the suspension handles that.

The objectives for developing a frame with suspension are much different than the objectives for conventional frame design. In a suspension racquet like a BOLT, the frame is no longer the element responsible for comfort and ball rebound speed control, the suspension handles that. The frame then can be made as stiff, strong, stable, lightweight and powerful as desired.

In fact, one of the best ways to optimize suspension performance is to provide a strong, stable frame for it to work from. As the frame is made stronger and stiffer, it becomes more powerful and more accurate of course, and the suspension works better - more efficiently.


A strong, stable frame also opens up possibilities for enhancing the response of the string-bed in other ways. For example, the head frame can have much larger string hole openings, or even open slots, which can increase effective string lengths greatly, allow the string-bed to deflect more and "swing" more freely, and even maximize the potential for string "snap-back" to occur - all while maintaining the structural integrity of the frame structure itself.

Greater frame strength and lighter weight will allow the ZIPSTRIP suspension of a BOLT racquet to be expanded to surround the entire string-bed. It will also enable potentially heavier versions of ZIPSTRIPs and/or other types of suspensions to be utilized as well, without diminishing a capacity to achieve desired weight and balance targets.


Further frame development can include combinations of frames and suspensions wherein a frame is made to flex in a specific way in order to harmonize with a chosen suspension - yet another avenue for exploration.


  • Improve strength to weight ratio

  • Optimize manufacturing techniques

  • Expand options for string openings

  • Expand ZIPSTRIP locations

Prototype #1: Super-Strong Frame

US Patent #9,132,321

This patented frame design-method utilizes a cutting edge composite manufacturing technique to make a multi-part frame with the potential to be stronger and lighter than any previous composite racquet. The first iteration of the design is a multi-part frame construction which results in a double internal wall structure around the head frame. The double wall makes the racquet supremely strong in all aspects of force resistance - bending, twisting, shearing and torsion. It also provides tremendous compression strength within the head frame profile, providing an ideal "foundational structure" for a ZIPSTRIP or any other type of suspension.

The super-strong frame structure allows for string openings to be much larger than on a conventional frame. Not only can the openings be larger, but they can be located in the most important locations around the string-bed as well. Larger openings means bigger string "swing", maximum "snap-back" potential, longer effective string lengths, and all are achieved without sacrificing the inherent strength of the underlying frame structure.

Prototype #2: Grommet-less ZIPSTRIP

US Patent #6,971,964

US Patent #7,927,239

​In the design of any modern racquet, minimizing it's weight is a critical factor. As a frame gets lighter, it enables greater opportunity to achieve optimum swing-weight characteristics. The grommet-less ZIPSTRIP design shown here will be significantly lighter than the Series X and Series XS ZIPSTRIPs and will certainly provide a far wider swing-weight capacity for future BOLT racquets.

This particular ZIPSTRIP design enables other technical options as well regarding the types of core materials that can be employed to affect/calibrate the impact-release response of the suspension.

Prototype #3: Suspension - RotoROCKET

US Patent #7,938,747

This is a new kind of suspension system which we will begin to test next year. The idea behind ROCKET is to provide a rotational suspension, and/or a rotational spring suspension, that absorbs less energy than a compression spring type. With less energy absorbed, the ROCKET, as the name suggests, will enhance more of the rebound or "spring-back" energy. Translation - POWER!

That's not all we have in store for tennis, but we can't show you everything at once, that would be boring wouldn't it!? Sneak previews to come!


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