Frame breakage - red alert - a Cowboy company statement says that some units of the C4 ST step-through model can develop fatigue cracks at the junction between the head tube and down tube. According to the data, these cracks can form after 2500 kilometres. This can result in the frame breaking.
Risk of frame breakage on the Cowboy C4 ST
This problem is due to a production deviation. It is a voluntary recall, they say. Cowboy offers two ways to check whether the frame needs to be replaced. Affected bikes can be identified by their serial number and frame manufacturer. There are two ways to check this:
- In the app: Select the "Advanced" settings icon to check the serial number and model. If the frame is listed as "Edition MR", it may be affected.
- The website cowboy.com/pages/recall to use the serial number checker
Registered riders of the C4 ST (Edition MR) model affected by this recall will also be contacted directly by Cowboy via email and the Cowboy app, according to the manufacturer. If the frame is affected, Cowboy will offer a free frame replacement.
The cause? Expert gives assessment
Ernst Brust from Velotech GmbH gives an assessment of the voluntary recall of the Cowboy C4 ST. The micromobility expert does not rule out the possibility of a fundamental design fault or at least a manufacturing design defect.
The fact that the start and end of the seam in the load fibre generate stress peaks in an already highly stressed area is particularly problematic. Brust emphasises: "Individual tests on the frame or fork are important - but even more important is the testing of the ready-to-use pedelec under realistic loads." Component tests according to the standard reveal important material and manufacturing defects, but do not necessarily show the behaviour of the entire construction in combination.
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Individual tests on the frame or fork are important - but even more important is the testing of the ready-to-use pedelec under realistic loads. - Ernst Brust, expert Velotech GmbH
However, the Product Liability Act and the European Product Safety Directive stipulate that the finished product must be tested before it is launched on the market - under conditions that can be expected in everyday use.
Safety relevance
A crack in the head tube down tube area can progress rapidly, says Ernst Brust. If the welded connection breaks completely, the rider immediately loses control of the front wheel - a fall with a considerable risk of injury is almost inevitable.
A complete end-of-line inspection would probably have prevented this case. - Ernst Brust, expert Velotech GmbH
Expert Brust summarises: "Only the testing of the complete, ready-to-ride pedelec can ensure that load combinations of design, braking system, chassis design, material and production are reliably mastered. Component tests alone are not enough to prevent complex weak points in the field."
Maik Schröder
Editor
