There are many reasons a spoke could fail: Catastrophic failure where someone puts a security chain trough the spokes and forgets, manufacturing flaws in material or drawing, and corrosion, but our spokes typically break because they have work hardened from cyclical stress.
If one was loose enough to work harden, are the rest of the spokes still tensioned correctly? Probably not.
Those little pieces of wire support these 500 pound motorcycles, are exposed to constant cyclical stress, and as such need to be pre-tensioned (or stretched) during wheel building. They are stretched just beyond the point where they would stretch during normal cyclical loading. The result of spokes being under tensioned is the spoke will eventually work harden, fatigue and fail.
A general rule I go by: For my personal bike (its' my hide), if one spoke failed, and all of the rest of the spokes are tensioned properly, than I would venture to change just one spoke. I would keep a close eye on the rest. If I was to do this for a customer, I feel there is only one way to do this job, and that is replace all of the spokes...
There is just too much liability, and the result is often more than an ouch. There is no practical way to know whether the spoke had a catastrophic failure from something stupid, failed from fatigue, work hardened from constant stretching because the spoke was not pre-tensioned, had internal manufacturing flaws from making of the steel or drawing the spoke, or had a crack failure induced by corrosion. The tests, while informative, would be destructive to the spoke.
John
