Possible causes for flange breakages on bicycle hubs

Spoke bend length is too short and/or the spoke diameter at the bend is too large

Effect: The spoke slightly deforms the flange as they are threaded and aligned into the hub shell or as the spokes are tensioned. This could lead to a flange breakage if this damage occurs at approximately 90° to the direction of the spoke tension. The source of the crack is the damage.

Stamping burr on the spoke head

Effect: The burr on the spoke head stamps itself into the hub flange leaving a notch at the countersunk spoke hole. If this notch is to be found at an angle of approximately 90°to the direction of the spoke tension, then the flange could crack. The source of the crack is the burr on the spoke head.

Loose spokes due to too long spoke bend length / too small diameter of the spoke at the bend / spoke tension to low

Effect: The spoke head of the unloaded spoke can move freely within the spoke hole of the hub flange, this in turn damages the inner surface of the spoke hole and leaves notches. The damage that can be found at approximately 90° to the direction of the spoke tension could lead to the hub flange cracking at this Point.

Re-lacing with alternative spoke alignment (second lacing of the hub)

Effect: The old embedment acts just like a notch or previous damage to the spoke hole. As this previous notch lies at an angle of approximately 90° to the new direction of the spoke tension, this could lead To the hub flange cracking at this point.