Axle failure

See other failures under 000.html.

Unknown history. Picture from http://www.mountainbikerides.co.uk/images/photos_ouch/snapped_axle.jpg as of 2004/11/14 with no accompanying text. This does not appear to be an overload failure, rather it appears the axle failed at a bearing support shoulder, presumably a stress raiser. The visible surface of the failure is dirty in a way that suggests long-term faituge.

In contrast to a Shimano freehub, this style of cassette hub has large bending loads on the axle, as does a freewheel hub. Chain tension bending loads for a given tension are highest when the chain is on large sprockets, whereas a freewheel has them highest when the chain is on small sprockets.

Some hubs use a similar design but some trim away all but a little bit of the shoulder, which would increase the axle flexibility and thus reduce the stress concentration.

As a design alternative, note that Bullseye hubs use a separate spacer betwen the bearings. Since the spacer is separate from the axle, it provides no location, but produces no stress riser. Also note that Bullseye hubs have spacers running all the way from dropout to dropout, and the inner bearing race is clamped between spacers. As long as the preload (axle clamping force) is sufficiently high, the spacers act as an axle of larger diameter than the ``axle'' which runs from dropout to dropout. It is not clear whether this broken axle used spacers between bearings. If not, the axle is under bending at a smaller diameter than if it used spacers.