Why don't bicycle wheels buckle?

Bicycle spokes are easily bent. When you sit on a bicycle, how come the wheels don't collapse?

Why don't bicycle wheels buckle?
Bicycle spokes may be easily bent if put under a bending load or will buckle if put under compression, but they don't stretch when put under tension. The rim is also fairly weak without the spokes and can be pushed or stretched out of round, but it still has some stiffness and its circumference won't easily change if it is distorted in this way.





When you sit on a bicycle, the hub tends to be pulled toward the ground. The spokes above the hub are under tension, transmitting the force to the top of the wheel rim. This would make the wheel rim collapse into an oval if it could do so without the sides of the rim to the front and rear of the bicycle sagging outward in the process. However, the spokes going to the forward and rear part of the wheel rim prevent the rim from going pear-shaped in this way.





The spokes are also not fastened to the center of the hub but to either side. This prevents the hub from deflecting sideways because half the spokes will be under greater tension if the hub tries to deflect in that way.





Finally, the rim cannot rotate with respect to the hub because the spokes don't run exactly radially from the hub to the outer rim. Instead, the hub flange is comparatively wide so that half the spokes are under tension if the rim tries to rotate forward with respect to the hub and the other half are under tension if it tries to rotate backward. Either way, the rim is not free to rotate.
Reply:When you sit on the bicycle, some spokes are under pressure. However the ones at the sides are under tension, and stop the wheel from buckling.



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