Hazardous bicycle handlebar stems (original) (raw)

SPLIT HANDLEBAR STEM EXTENSIONS

ARE HAZARDOUS!

� 2001-2003, John S. Allen

Bicycle component designs are proven reasonably safe -- or not -- through engineering analysis and testing -- or else through failure in use. It is disturbing to discover components which look as though they should be reliable, but which have serious engineering flaws. Certain handlebar stems provide examples of this problem.

The forward extension of the traditional aluminum alloy handlebar stem is a solid shaft, with a transverse, cylindrical opening at the front for the handlebars. To allow the handlebars to be clamped securely, the handlebar opening is split at the bottom or at the front, where it is subject to relatively light loading. A bolt pulls the two sides of the split together to clamp the handlebars.

The forward extension of the flawed stems is split behind the handlebars. To the untrained eye, a split shaft would seem to be as strong as a solid one, but it is not. Consider the example (photo below) from a French-made child's bicycle. This stem does not need a separate bolt to clamp the handlebars in place, because the bolt that secures the frame to the fork tightens the stem around the handlebars as well.

It might seem that the top and bottom halves of the split forward extension of the stem are both securely connected to the quill (vertical part) of the stem -- after all, the lower half of the forward extension is continuous with the quill, and the upper half is connected through a rigid steel bolt.