Originally Posted by
SquidPuppet
Here is my non qualified opinion on that. All the important stress, fatigue, and torture occur where the steerer joins the crown. That union needs to be STRONG. The threads at the top allow the top race to be positioned (not tightened) to set proper bearing preload, and a lock nut to be gently snugged, simply to prevent the race from coming out of adjustment. That's it. There is no top-to-bottom tension on the steerer, or the threads. Gravity and rider/bike weight hold it all together.
Yeah that's true. The crown race and the bottom cup pretty much take all the load. Top is there for centering.
There would be
some top to bottom tension induced by side load wedging action across the ~conical races. One could argue it's incidental, but it's not zero. Never thought of this till right now, but it would seem that this effect might be minimized in headsets because both cups and both 'cones' face the same direction. They are not mirror imaged as they are in hubs and BBs. So a side load won't have as much tendency to wedge them apart. Someone must have figured that out like 130 years ago...