Classification of bicycle derailleurs

Bicycle derailleurs are also divided into external derailleurs and inner derailleurs, as follows:

External gear
The tower-shaped multi-stage tooth plate is used, and the chain is matched with the tooth plate of different values to obtain a wide range of transmission ratios.
Advantages: easy maintenance, transmission effect is clearly visible
Disadvantages: The structure is basically exposed and vulnerable to dust and foreign objects, causing damage.

Internal gear
The speed change structure is integrated into the bicycle hub, and the transmission ratio is changed through the transmission between gears with different numbers of teeth.
Advantages: The structure is sealed, not affected by the outside world, and generally does not require frequent maintenance.
Disadvantages: complex structure, thick shell, heavy quality.