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Spindle Failure — Square-Taper, Solid

Square-taper spindle failures in square section at the end nearest the center:

From a Schwinn LeTour circa 1980; usage history unknown.

Square taper spindles typically fail at the large end of the square taper. The square section is significantly weaker than the round section, and bending and torsional stresses are high where the spindle exits the arm.

Note this is a "nutted" spindle which is solid, not hollow. People sometimes assume a solid spindle is stronger, but a hollow spindle has very nearly the same strength as a solid one of the same material — because most spindle loads are carried near the surface of the spindle and not at the center.