How can it be considered a good frame?

Lightness, firmness, and good elasticity are one of the goals pursued by frame manufacturers. To achieve this goal, it depends on the craftsmanship of each frame manufacturer. Whether the designed frame is designed based on the strength and characteristics of the material, and whether the welding process is mature. These all directly affect the appearance, strength, and elasticity of the frame. Another important thing is spray painting. 

A good frame should be evenly painted and sprayed with 3-4 layers of paint. Don't underestimate spray painting, good spray painting can make bicycles easy to maintain and less prone to rusting. If a frame that does not meet the above requirements is used for loading, it is possible to produce bicycles that cannot be ridden in a straight line or are difficult to turn, or bicycles that quickly break down.