I am testing all frames using the ISO4210-6 methodologies before delivering each bike for:
- pedalling forces fatigue
- frontal (braking) forces fatigue and
- vertical forces fatigue
The fatigue tests will be set at 10,000 cycles.
Composite fatigue failures follow a fairly extreme version of the bathtub curve: if a composite frame is going to fail in fatigue, it will do so in the first few thousand cycles or after millions of cycles, but not between. The “bottom of the bath” is a near zero failure rate.
There was an interesting podcast recently on Cycling Tips covering testing and custom builders, I think this is well worth listening to. One thing that got a bit glossed over in this discussion is that the fatigue tests specified in ISO4210-6 are a bit of a compromise between short cycle and long cycle fatigue, but this has an interesting consequence that was mentioned: both Nick Crumpton and Ben Shultz say in the podcast that they are still riding bikes that have been through the fatigue test. As has my own Lyrebird bike. However, “smaller custom builders typically don’t conduct much, if any, bench testing to qualify their creations before they head out the door.”
Another interesting part of the discussion is there’s an inherent bind faced by all custom builders: where production builders can test a representative sample of each size of each frame and generate a statistical model to predict failure rates. So they can predict safety rates for the production run as a whole. This is impossible for a custom builder because each frame is unique.
The podcast mentions that even if we built a duplicate frame and tested that, this would still not work because it could not take into account small variations in layup and possible voids and inclusions.
Putting these two concepts together suggests an out. Lyrebird has in house testing capabilities so it is practical to test every frame for a few thousand cycles on the fatigue tests. 10,000 cycles will be enough to get to the floor of the bath but not enough to materially affect longevity. This will only take a few hours per test. Remember the motto: Be safe or be road kill.