Steer Tube Failure

See other failures under 000.html.

From http://velonews.com/news/fea/9076.0.html 2005/10/28, dated 2005/10/24:

Our latest reader-submitted Photo Gallery is now up for your viewing pleasure.

Of course, a new gallery also means the naming of the winner of our most recent contest. Becky Brandt's "Uh-oh this is gonna hurt" received the same initial reaction from nearly everyone we showed it to: "OUCH!!!" Even though the equipment - and probably the photo itself - are decidedly old school, the shot captures the precise moment that poor rider's day went to the dogs. (We hope he did better than we suspect that he did.)

Congratulations, Becky! Contact us and you win a copy of Graham Watson's "Landscapes of Cycling." (We'd be grateful, though, if you told us the rest of the story when you write in to claim your prize.)

From http://www.velonews.com/news/fea/9082.0.html as of 2005/10/28, dated 2005-10-26:

Hello,

Becky Brandt's dad here. Becky is at school right now, so I am writing in on her behalf. She took that photo at the WORS Ultimax Challenge in Sheboygan, Wisconsin, on October 9th of this year. It was the citizen/beginner race in the area simply called "the log jump." This guy hit the jump pretty fast, but never pulled up on the bars at all. The fork steer tube sheared at the threads when he was landing. He turned out to be okay. Nonetheless, they took him in for a visit to the hospital as a precaution.

While he was laying on the ground, he was asking his dad to pick up the headset bearings and other parts so he could rebuild and give her another go!

Thanks for the weekly photo contest. We have had a lot of fun with it!

Doulas Brandt
Kenosha, Wisconsin

Mmmmmm... "Rebuild her and give her another go?" Maybe he should have been more thoroughly examined. Anyway, please give Becky our congratulations. Her book is on the way. - Editor

This picture is also an interesting case study in analyzing photographs. Several notes:

• The bicycle and clothes look to be from the mid 1990's. Without further information it is unclear whether this is an old photo of new equipment or a new photo of old equipment.
• There are clues this is immediately following a jump landing including
  • Front tire is compressed.
  • Several spokes appear bent, as if slackened.
  • Chain is deeply slackened. See picture below. (Effect probably exagerated by running on the small chainring so the chain was already loose.)
  • Rear tire is off the ground.
• The top bearing race and locknut came off with the stem. This suggests the steer tube failed below the bearings, and not that the stem failed.
• The rear brake cable appears to have come disconnected.
• It appears the front brake is a cantilever and the arch wire and cable saddle have been dragged forward by the brake cable and/or cantilever spring tension. This would tend to jam the front tire.

The nature of the failure is unclear. An over-tight stem bolt can swell (distort) the steer tube. If the stem has slight insertion and/or the steer tube has long threads, the swelling can occur in the threaded area, which is weaker. Slight stem insertion tends to increase the bending load on the steer tube. Wheel loads from landing will principally be along the steering axis, so bending load on the fork will be small except for the stem loads. We have no knowledge of the service history of the bicycle.

See also FAIL-046.html.