The upper part of the chain cover on bikes or motorcycles is commonly referred to as the chain guard, while the lower part is often left uncovered. There are a few reasons why this design is implemented:
Protection: The primary purpose of the chain guard is to protect the rider and other nearby components from contact with the moving chain. By covering the upper portion of the chain, it helps prevent loose clothing, shoelaces, or other objects from getting caught in the chain, which could result in accidents or injuries. The lower part of the chain, on the other hand, is closer to the ground and less likely to pose a hazard, so it may not require full coverage.
Accessibility: Leaving the lower part of the chain exposed makes it easier to access for maintenance and adjustments. When the lower portion of the chain is uncovered, mechanics or riders can easily lubricate, clean, or adjust the chain tension without having to remove or disassemble a complete chain cover.
Weight and Cost: By eliminating the lower portion of the chain cover, manufacturers can reduce the weight and cost of the motorcycle. The lower part of the chain is less likely to come into contact with external objects or pose a direct safety risk, so it may not be necessary to cover it fully.
It's important to note that the design of chain covers can vary between different motorcycle models and manufacturers. Some bikes may have full chain covers that enclose both the upper and lower portions of the chain, while others may have partial or minimal coverage. The specific design choices are influenced by factors such as safety considerations, accessibility, weight reduction, and cost efficiency.