Originally Posted by Carbonfiberboy

The problem is that you didn't go to engineering school and take materials science and statics. Think about the concepts of tension and compression while holding a toilet paper or paper towel tube in your hands. Try to bend it without collapsing it. The tube is extremely light yet not that easy to bend. Holding it in front of you and trying to bend the ends down, the top is in tension and the bottom is in compression. That's a frame tube, hard to bend, i.e. stiff. Materials which are hard to stretch and compress like carbon fiber/epoxy laminate make a very stiff frame tube. Plus you get to vary the stiffness by the thickness of the laminate. Plus it's not carbon cloth like in the photo. It's "tows" of unidirectional fibers running lengthwise, but at some slight angle to the long dimension of the tube. Thus the tube is also stiff rotationally. Plus you can vary the rotational stiffness vs. the longitudinal stiffness just by changing the angle of the carbon tows. Carbon fiber structural design is not a simple thing, not at all. With metal, the builder is limited to what is made commercially, diameter, wall thickness, and alloy. Not so with carbon/epoxy. Pretty easy to see why carbon is such a popular material.