Originally Posted by
kpfeif
I think it's a little nonintuitive. Here's the explanation from Jobst:
Wheel stresses (Jobst Brandt)
Another way to think of it is to draw the wheel. Each spoke is under tension and exerts a force outward that keeps the hub stationary in the center of the wheel. When a rider is pressing down on the hub, there needs to be a force in the opposite direction to keep the hub in the same place. This force is coming from the ground, through the lower spokes, back to the hub and is equal and opposite the force exerted by the rider. Of course the whole wheel is under tension, so rather than the lower spokes being compressed like the legs of an elephant, they experience "compression" from a state of high tension to one of lower tension, but remain in tension. Unless, that is, your wheel isn't under enough tension - then bad things start to happen.
Probably the only way to convince yourself is to try it with your bike. Lean over the front handlebars and pluck the lowest spoke, with and without putting weight on the bars. Now do the same for the opposite (upper) spoke. You'll find that the pitch of the lower spoke drops when the wheel is weighted (because the tension decreases), while the upper spoke keeps the same pitch. It's hard to get your head around it until you try it yourself.
That is how I understand it, but as a non-engineer it can be difficult to know where one stands whether in Jonestown, or the Vatican.
As explained I don't understand what the DB spokes are doing, what are they designed to do, and how do they do it. The best I can imagine is that when one puts a spoke under tension if one graphed the input vs tension, it would be a steeper line with the straight spoke. If you pull on a spring it will move a long way before target tension is reached, but pull on a carbon rod the line will probably go straight up (vertical axis tension on spoke, horizontal axis extension in spoke. That would mean that in reverse, during compression loading the same length movement in a straight spoke would take it completely out of tension where the DB might remain in tension over a similar movement. And to some extent the movement is also a period thing where it takes time but at a given speed one has already moved onto the next spoke. Anyway, that is what I see in it, but all the explanations I see relate to stretching in tension.