Each seatpost will be marked with a section of scale, and this section of scale is what we call the safety line mark, of course, it can also be used as a height mark, so that it does not need to be adjusted when the seatpost is removed and reinstalled.
The safety line is very important. The minimum installation height marked on the line is determined by the material and diameter of the seat tube. Therefore, when we install the seat tube, the height of the pull-out must not exceed this safety line. If it is not long enough, then a longer seat tube should be replaced.
During riding, many people saw off the excess seat tube in order to reduce the weight. At this time, the so-called safety line has lost its meaning and cannot serve as a mark. The basic principle is that the seat tube is inserted at least The frame is 60mm to ensure firmness. Of course, sawing off a little bit of the seat tube is very small in terms of weight. If it is really the most weight sensitive, then it is better to replace a carbon fiber seat tube.
There are also some car heads with safety lines, such as small head tubes, and ladies’ cars with gooseneck risers, etc. When installing, we must remember that the safety line is there.