Originally Posted by alan s

Here is another experiment you can try at home. Roll up a mouse pad, which represents a rim, hold it in your hand, and looking at it end on, press your finger into the side at one point. Your finger represents the ground. You will notice the mouse pad flattens inward where you press your finger, and bulges outward beyond that point. The outward bulging decreases to zero opposite of where you press your finger.

The imaginary spokes on either side of where you press with your finger would counteract the bulging, keeping the mouse pad round, and the tension on those spokes would increase slightly as a result. The only spokes that would show noticeable detensioning are those at the contact patch, due to deformation of the rim inward.

Of course, a wheel rim is made of metal or carbon and is held in place by spokes, so the deformation is very small. In addition, the tire and air inside help spread the compression load over the couple inches (the contact patch).