Bicycle Electric Transmission System

Project Background

In the early 2000s, Shimano officially entered the era of modern electronic shifting. The new technology attracted significant attention from investors, including one of our clients—an enthusiast of the Tour de France and a representative of a major Western European family sponsoring a professional cycling team.

During that period, most Tour de France teams adopted Shimano’s first-generation electronic shifting system. However, the system faced several challenges that impacted both performance and bicycle design flexibility.

Key issues with the first-generation system included:

• Bulky wiring and connectors: The cables were thick and required large connectors, making disassembly difficult and limiting frame compatibility. The wiring could not be fully concealed and only worked with specific bicycle models.
• External battery with low cycle life: Teams reported that during rainy stages, the external battery occasionally failed. In long-distance races, there was roughly a 20% chancethat teams needed to replace the battery mid-race.

Meanwhile, bicycle manufacturers such as Trek, Cervélo, Specialized, Giant, and Cannondale were rapidly innovating. Yet many team managers voiced complaints: the frame designs could not be significantly updated to fit Shimano’s early system. As a result, several manufacturers continued relying on mechanical shifting for stability and reliability.

Our client was one of these team sponsors, and their racing results suffered as a consequence. Determined to change the situation, he decided to invest in developing a superior electronic shifting system that could rival or surpass Shimano’s offering.

Key Challenges

• Extremely limited battery space inside bicycle frames.
• Requirement for an internal battery system rather than external mounting.
• Higher waterproof and dustproof performance is necessary for professional racing.
• Longer operating time to prevent mid-race battery changes.
• Lower self-discharge to ensure bicycles that sit unused for a period can still operate reliably.

Our Solution

Electrical & Structural Design Support

The client partnered with a professional drivetrain engineering firm to design the electronic transmission system. They developed a fully internal, compact, water-resistant system based on his specifications.

Battery Solution by PKCELL

PKCELL was selected as the battery technology partner. Given the severe space limitations inside the frame, we proposed Lithium Polymer (LiPo) battery technology due to its thin, flexible structure and high energy density.

Key elements of our battery solution:

1. High-Voltage LiPo Technology

We were the first to adopt higher-voltage LiPo chemistry for this application.
Benefits included:

• Significantly increased capacity within the same physical volume
• Longer continuous shifting time for riders
• Improved system responsiveness and performance

2. Low Self-Discharge Materials

To address the issue of bicycles sitting unused for long periods, we selected battery materials with very low self-discharge rates, ensuring consistent performance even after extended storage.

3. Comprehensive Environmental Testing

PKCELL conducted extensive testing, including:

• Waterproof & dustproof verification
• Cycle life testing
• Long-term self-discharge evaluation
• Road vibration & shock testing for real-world racing conditions

Although the overall development period was longer than initially expected, the final product achieved excellent performance.

Results & Value Delivered

• The client successfully launched his electronic transmission system shortly after the release of Shimano Ultegra Di2 (6770).
• The system earned strong market acceptance and continues to maintain a stable market share across European countries.
• The internal battery pack designed by PKCELL became a key differentiator, delivering higher capacity and stronger reliability than most competitive systems of that time.

Next Steps

The client is now developing a wireless electronic shifting system, and PKCELL remains the exclusive battery partner.

His next strategic goal is to expand into the North American mid-range bicycle market, aiming to compete with mainstream brands and gain significant market share.

The battery solution became the core advantage of our transmission system. PKCELL ensured performance, durability, and confidence for professional racing.