The seam between the door and the fender should be moderate. The fender hit the door and damaged the paint. When opening and closing the door, the gap between the fender and the door is too small. The fender will rub against the door, and if the paint is not found out in time, it will damage the overall safety performance and maintenance cost of the vehicle. The gap between the fender and the door is too large, which will cause abnormal sound to the overall beauty of the vehicle. If the speed is too fast, there may be abnormal noise in the car, and wind noise will be introduced into the car through the gap, reducing the comfort of the drivers and passengers.