Tube Bed Failure

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"H Plus Son" brand "Formation Face", tube bed failure while skidding, rear wheel.

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More pictures at http://www.flickr.com/photos/ganring/sets/72157609868064447/ as of 2009/01

The report does not indicate whether the skid was straight ahead or sideways. A sideways skid would likely increase the spreading force on the rim bead hooks.

That said, tube bed failure is uncommon unless there is a design or manufacturing defect such as hard anodizing or an extrusion notch causing a stress riser.

According to http://www.hplusson.com as of 2009/01/08, rim weight is nominally 580g +/- 15g; the rim is made of G609 aluminum alloy; and available drillings are 32 or 36 spokes.

From photos, it appears to be a 32-hole rim.

The failure appears to have started at or near the vavle stem.

Tire pressure at time of failure was not reported. The tire is likely a 23mm Vittoria, 23mm is typical for a 19mm rim.

Rim was 2 weeks old at failure.

Nominal rim section is:

Rim weight is nominally 580g +/- 15g compared to a Velocity 30mm x 19mm rim at nominal 520g. The much taller section but only slighly higher weight suggests the wall thickness of the rim is thinner, and the rim section drawing and photos suggest thinning extends to the tube bed. With many spokes, there are many spoke holes and corresponding weakening of the rim bed.