The following is a Sponsored Article in Partnership with Bafang

In the world of eBikes, the battery and the motor together form the foundation of the product. The choice of motor type, particularly the difference between inner rotor and outer rotor, often determines the overall performance characteristics and riding experience. As a leading supplier of eBike drive systems, Bafang uses over 20 years of technical expertise to guide you through this technical discussion about the “heart of the eBike”.

Basic Principles: Structural Differences Between Inner & Outer Rotor Motors

Structurally, in an Inner Rotor Motor, the rotor is located inside and rotates, while the stator is fixed on the outside. Conversely, in an Outer Rotor Motor, the rotor rotates on the outer circumference, encasing the stator at the centre.

Diagrams below: Inner Rotor Structure, Outer Rotor Structure

Inner Rotor Structure Outer Rotor Structure scaled Inner Rotor vs. Outer Rotor: Bafang Delves into the Core Differences of eBike Motors

This fundamental structural difference directly impacts the motor’s efficiency, noise, cost, and applications.

Performance Comparison: Each Has Its Advantages for Specific Scenarios

In the eBike sector, most motors feature a “stator + rotor + gear reduction mechanism” design, which is also where Bafang’s technical strengths are concentrated. For ease of understanding, the following comparison is based on motors with gear reduction mechanisms and similar sizes:

For motors with gear reduction mechanisms and similar sizes, the Inner Rotor Motor and Outer Rotor Motor present distinct performance characteristics. Regarding Noise & Vibration, the Inner Rotor motor’s bridge structure results in smaller speed/torque fluctuation, smoother operation, and low noise, while the Outer Rotor motor’s cantilever structure leads to larger speed/torque fluctuation and high noise. Looking at Structural Complexity, the Inner Rotor is a complex structure with high manufacturing cost and high maintenance requirements, in contrast to the Outer Rotor’s simple structure, moderate manufacturing cost, and moderate maintenance requirements.

In terms of Reduction Ratio Suitability, the Inner Rotor is ideal for high reduction ratio applications and offers higher transmission efficiency, whereas the Outer Rotor is suited for low reduction ratio applications and has a more compact structure. Finally, concerning Power Density, the Inner Rotor motor has fewer magnetic pole pairs, resulting in lower consumption, higher efficiency at high speeds, and high power density. Conversely, the Outer Rotor motor features more magnetic pole pairs, which translates to higher consumption, lower efficiency at high speeds, and low power density.

Structure diagrams: Bridge Structure, Cantilever Structure

Bridge Structure Cantilever Structure Inner Rotor vs. Outer Rotor: Bafang Delves into the Core Differences of eBike Motors

Bafang Hub Motor Structure Examples: Inner Rotor Gear Reduction Structure

Inner Rotor Gear Reduction Structure scaled Inner Rotor vs. Outer Rotor: Bafang Delves into the Core Differences of eBike Motors
Inner Rotor Gear Reduction Structure

Outer Rotor Gear Reduction Structure scaled Inner Rotor vs. Outer Rotor: Bafang Delves into the Core Differences of eBike Motors
Outer Rotor Gear Reduction Structure

Bafang Product Examples:

Inner Rotor Motors, suitable for eBike models requiring excellent noise control and high transmission efficiency:

  • H700 (250W Auto 2-Speed Hub Motor) – Urban Commuter eBikes
  • H410 (250W Hub Motor) – Urban eBikes
  • H650 (3000W Hub Motor) – Off-road & Leisure eBikes
  • M210 (250W Mid-drive Motor) – City and Tour eBikes
  • M620 (1000W Mid-drive Motor) – Mountain eBikes

Outer Rotor Motors, better suited for models prioritising cost-effectiveness and structural simplicity:

  • H300 (250W Hub Motor) – City and Tour eBikes
  • H550 (750W Hub Motor) – Fat-tire eBikes

Please note that the motor is just one part of the eBike system. The seamless integration of the controller, battery, display, and overall bike design is equally crucial. We are committed to providing complete interconnected drive solutions, ensuring every eBike equipped with a Bafang system delivers outstanding performance and reliable quality.

Technology Serves the Experience

There is no absolute superiority between inner rotor and outer rotor motors; the best choice is simply the one that fits the user’s needs. Bafang consistently adheres to a “user-centric” R&D philosophy, continuously advancing the innovation and integration of motor technology. Bafang believe the future of eBikes will be smarter, more efficient, and better serve the personalised needs of every cyclist.

Bafang hope this article helps you gain a deeper understanding of motor technology and choose the right model. 

On your riding journey, Bafang is with you all the way!