Anatomy of a Failed Bicycle Spoke

The other day on the way to work I herd a "tink" from the front wheel sound as I came to a stop. I looked down and there was a spoke hanging off the hub. I got off the bike, removed the spoke then put it in my back pack. I loosened the brake adjuster a bit so the wheel would turn and continued to work.

When I got to work I had a look at the broken end and noticed that it had the classic marks of a brittle fatigue fracture. Not wanting to miss the chance to document a failure I took a couple of pictures. The wheel had over 7000 miles on it when the spoke. Using a circumference of 210cm, yields 5.7 million cycles on the spoke. This is plenty of cycles to cause a fatigue failure. This type of failure typically takes place in three phases.