Originally Posted by
PennyTheDog
I've been fiddling around with finite elements software for estimating material stresses recently-- I'm going to see if I can model this today, because I'm curious about about how much the stress is increased here. However, that's a steel fork with a steel steer tube, right? Steel deforms plastically so much before it fails, I think the fork would be noticeably deformed for quite a while before it failed. I wouldn't think you'd have to worry about it snapping without warning. Am I wrong about that?
When you model, be sure to factor the thread depth and the fact that the stem ends at a thread. If you're curious you might run two models, one with threads and one without. And yes, steel steerers are moderately ductile, and would tend to bend slightly before breaking, but unfortunately there's no time gap and both will happen within a microsecond as a single event. There's no way the rider could ever see a warning sign of impending failure.
I might add that forks have been breaking below the headset for a long time if threaded beyond the stem depth. That's why it's been SOP for a for forks to be threaded less than 2" or so, while stems are inserted at least that far, ensuring that the stem ends below the last thread.