Originally Posted by
HillRider
This can get into a real semantic argument; does a bicycle wheel hang from the top spokes or stand on the bottom ones? Go argue with Jobst Brandt about this and get back to me on the outcome.
Obviously the static loads are all tensile but under weight and riding forces the bottom few spokes come under compressive loads so they lose some (sometimes all) of their tensile loads. The upshot is that the load changes from tensil to less tensile or, for a low tension wheel or a hard bump, even a compressive load.
Not quite obviously all of the loads on a tensioned bicycle wheel spoke are tension and sheer loads; tension in the middle section of the spoke that we test with our ear or tensometer, a sheer force at the elbow (yes also a slight compression force there too). I don't need to argue with J.B. He'd back me up in saying that bicycle wheels hang from the upper spokes and the bottom spokes may have a reduced tension due to the load placed on the axle, but they are not in compression. I think its been said already, but I'll reiterate that a bicycle wheel is a system of dynamic tension loads. The theory of butted spokes is to keep the same amount of material at the rim and hub flange where most breaks occur, but reduce material in the center to save weight and possibly to also provide more elasticity. The only wheel (bicycle type) that loads its spokes compressively on purpose (other than spin,aerospoke,spynergy,etc) is this new mavic money grabber (
http://roadmag.blogspot.com/2007/06/...take-note.html). I'm not trying to flame anyone (uh oh, I've probably just started a war with that comment
) but its science.
I've always been pleased with Colorado Cyclist's prices, selection, and service for ordering spokes.
Edit: I was wrong. At some point I must have been told, and bought, the old "hanging from the middle" story. Testing the spoke tensions on a loaded wheel does not bear this out. The bottom spoke is definitely the only one that experiences an appreciable change in tension (less).