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Deep-section Rim Failure At Pinned Joint

Deep-section rim failed at pinned joint. From https://www.flickr.com/photos/63373992@N07/13969154887 as of 2014/08. This is a side view of a deep-section aero-prifle rim, looking at the brake track (right) with the spoke bed at the far left.

No reports of rider injuries. Service history unknown. No notes on how the failures were discovered.

Make and model and spkes/lacing of rim not listed. From the photograph, the rim is probably at least 30 mm deep.

The phtotograph shows the anodized brake track is not worn through. This suggests either little use or use almost exclusively in dry weather, as wet riding tends to stick abrasive dirt to the rim which quickly wears off anodizing.

There is some slight anodizing wear right at the joint, this often occurs normally because the joint is never perfectly-aligned.

Text at the above page says:

There are 2 steel pins holding the rim together. [...] This is a sponteneous failure and not caused by an accident.

Additional text is not entirely clear, but suggests the rim was twisted at rest (e.g., with the pins removed), and it may have been twisted at the factory and sprung in to alignment, then some kind of pin or other failure allowed the rim to return to the original shape.

Two pins probably provide local stability but not much resistance against twisting. An alternative used in some rims is an aluminum extrusion that fits in side the rim section and serves as a "pin", but can reach the full height of the rim hollow and thus provide more precise alignment.

Note that when a rim is formed, it is initially a hollow tube and then bent in to a "coil", then sawed. The "coil" shape is necessary as the bending machine needs to use material beyond the end of the final rim in order to do the bending. Once a rim is formed, it is possible to saw off the excess then run the rim through extra steps to align it. Doing so should improve the rim truness, but is also added manufacturing expense.