Originally Posted by
scott967
At the risk of jumping into this thread mid-stream, I think you are considering the net forces on the spoke, while what you referenced is only the additional sinusoidal force applied as the loaded wheel rotates. Clearly when the wheel is built there is a tension force on the spoke. What I get from what you quoted is that the tensioned spoke acts as a column WRT to the ADDED compressive force so when considering the effect of the compressive force, treat the spoke as a column. Again, it says nothing about the net force, which has to be tension.
scott s.
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Yes, I think he's considering it this way. As a whole, the wheel undergoes compression and its resistance to that compression is what holds the bicycle by the dropouts. I think it's an unnecessary simplification that serves no purpose. Of COURSE the wheel is opposing the compressive force of the dropouts on the hub. Otherwise the bike wouldn't function. The downward force of gravity is being opposed by an equal and opposite force from the wheels. But the way the wheel achieves this is not by compression. He explains earlier in the book about how a wagon wheel IS a compression wheel and acts completely differently than a tension bicycle wheel. (Unless, of course the wagon wheel's spokes are so well attached that the top spokes undergo tension forces as the bottom spokes undergo compressive forces, thereby sharing the overall load or force. Then it gets more complicated.)
But that doesn't happen in a bicycle wheel. Tension wheel spokes, as almost always configured, cannot tolerate individual compression loads. They can only go to zero tension and stay there. They cannot be compressed because the are not supported in that direction - they simply push out of the spoke holes or eyelets.
This, again, is why his discussion makes no sense to me. Again, I may just be incredibly stupid. My wife tends to think this
