A planetary gear (also called planetary wheel gear) is a special type of gear that is also used in e-bikes – especially in hub gears or motors, such as mid-engines.

Structure of a planetary gear

A planetary gear typically consists of three main components:

1. Sun gear (in the middle)

2. Planetary gears (several gears that revolve around the sun gear)

3. Ring gear (also “hollow gear” or “standing gear”, external with internal teeth)

The planetary gears are mounted on a carrier (the planet carrier) and rotate both around their own axis and around the sun gear – similar to how planets orbit a sun, hence the name.

Advantages of a planetary gear in an e-bike

✅ Compact and efficient: The gearbox transmits a lot of power in a small space - ideal for e-bikes with limited installation space (e.g. in the motor or in the hub).

✅ Low maintenance: In hub gears, the gear runs encapsulated and protected from dirt and weather.

✅ Durable: Due to the even distribution of force across several gears, wear is low.

✅ Load change resistant: It can handle high torques well – especially important for powerful mid-engines.

Areas of application on e-bikes

🔧 Hub gear with planetary gear
Examples: Shimano Nexus, Rohloff Speedhub
– These transmissions use an internal planetary gear system to select gears (usually 3–14 gears). The advantage: you can shift while stationary.

🔧 Motors with integrated planetary gear
Examples: Bosch Performance Line, Brose Drive S
– Many mid-engines use a planetary gear system to transfer torque from the engine to the crank.

Disadvantages

❌ Weight: Can be slightly heavier than derailleur gears.
❌ Efficiency losses: Minimal loss compared to direct chain guidance with derailleur systems.
❌ Complexity: The technology is more complex and difficult to maintain for laypeople.

Conclusion

A planetary gear is an extremely clever, compact, and robust power transmission system – perfect for the demands of modern e-bikes. Whether in the hub gear or the motor, it provides low-maintenance, reliable, and powerful assistance while riding.