How does the Rear Derailleur receive the chain from the front derailleur and connect it to the rear wheel for power transmission and shifting?

The basic structure of the Rear Derailleur is mainly composed of an upper guide wheel, a lower guide wheel and a cage-type bracket. The upper guide wheel has a sliding gap, which plays a key role in providing flexible guidance for the chain during the shifting process, ensuring that the chain can smoothly enter the control range of the Rear Derailleur. The lower guide wheel always holds the chain tightly, mainly responsible for tensioning the chain to prevent the chain from falling off or loosening during movement. The cage-type bracket is responsible for fixing the guide wheel and guiding the chain to move along the predetermined path.
In terms of working principle, the chain first passes through the front derailleur and then enters the upper guide wheel of the Rear Derailleur. The upper guide wheel provides flexible guidance for the chain through its sliding gap, allowing the chain to smoothly enter the control range of the Rear Derailleur. When the rider turns the shift handle, the shift cable pulls the Rear Derailleur, causing it to achieve lateral displacement through the internal parallelogram linkage mechanism. This lateral displacement enables the chain to move from one tooth of the flywheel to another under the guidance of the Rear Derailleur, thereby achieving the speed change function.
During the movement of the chain, the lower guide wheel always plays an important role in tensioning the chain. It ensures that the chain maintains proper tension during the movement to avoid loosening or falling off. At the same time, components such as the tension spring inside the Rear Derailleur will also work together to further ensure the tension of the chain and ensure smooth and stable power transmission. When the chain moves to different flywheel teeth, the transmission ratio changes accordingly, thereby achieving speed change. This change in transmission ratio will directly affect the rider's pedaling torque and the angular velocity of the wheel, allowing the bicycle to adapt to different road conditions and riding needs.
In terms of details and optimization, the design of the guide wheel has a significant impact on the chain's buckle angle and resistance. The larger the guide wheel, the lower the chain buckle angle, and the smoother the ride. In addition, the Rear Derailleur is usually equipped with limit screws, such as H limit screws and L limit screws, which are used to limit the movement range of the Rear Derailleur to prevent the chain from moving outside the flywheel or interfering with other components. Some Rear Derailleurs are also designed with tension screws, such as B screws, which are used to adjust the distance between the chain and the flywheel teeth to further optimize the speed change performance and improve riding comfort and efficiency.