The frame is like a person's skeleton, which determines the performance of the car. The frame has high precision, high strength and light weight. Eleven good frames are the most ideal goals. Common frame materials are metal iron, which can be divided into three types: chrome-molybdenum alloy copper steel, high carbon steel, and ordinary steel. High-end professional frames are also made of aluminum alloy, carbon fiber, and titanium alloy. Whether the welding process of the frame is good, and whether the paint layer is uniform and shiny.
          The parts installed on the frame have their own functions. Good parts pay attention to light weight, high strength and good performance, so that the bike can be easily and safely driven. The parts of the bike determine the price of the bike. The parts used in professional cycling competitions are all high-quality components.           Even if there is a good frame and good parts without good assembly technology, the same assembled bike will be uncomfortable to ride. You should check carefully whether the front and rear wheels are in the middle of the front fork and rear fork. Whether the wheel rotates smoothly, whether the pattern direction of the tire is correct (the pattern arrow is forward is correct), turn the wheel to check whether the two wheels are offset, radial runout: handlebar, front and rear mud removal, whether the front clip of the shelf is installed correctly: yes The phenomenon of single-sided brake: whether the front vertical rod and seat cushion rod exceed the safety line: the joint of the front vertical rod cannot face the left and right scale lines of the handlebar: whether the parking frame is in good condition: whether the position of the brake block is on both sides of the rim In the middle part, how is the braking performance: Are all the screws locked and have the torque standards met: Are the handlebars and saddle heights suitable: Is the transmission system flexible? How tight is the chain? Finally check the paint for damage.