Metal Fatigue

Fatigue is the weakening of a material under repeated loading and unloading. Each cycle may be far below the force needed to break the part, but over thousands or millions of cycles tiny cracks start, usually at sharp corners, welds, holes or scratches, and grow until the part suddenly fails.

On motorcycles, fatigue cracks appear in frames and subframes near welds, in handlebars, footpeg and exhaust brackets, wheel spokes, and in bolts that were not tightened to the right torque. Vibration, overloading and off-road impacts speed it up. Aluminium has no fatigue limit, so it can eventually crack even at low stress.

Check high-stress areas when cleaning the bike, look for cracked paint or rust lines at welds and replace bent or cracked parts instead of straightening them.