This is a highly stressed component, particularly if you are running big brakes, slicks or sticky tires and performing threshold braking. Notice the rusted area, and then the fresh metal in this break. This tubing has been cracked for some time. Cracks will generally propagate from or along the edge of a weld. Generally, a good clue that a part is cracked, is by finding a hairline crack in the paint or coating. Once in a while. a crack may be sub-surface, and give no clues.