How tires are made, and what the various parts of a tire actually do.
Typically, people don't spend a lot of time thinking about their tires, after all, why should you? They just work. But a tire is quite an amazing piece of engineering once you get inside it. A tire has to hold up tons of weight on a cushion of air, stay in good contact with road surfaces, give excellent grip and flex when those tons of weight go around a corner and spring back exactly to its original shape. And it has to do this over and over for literally millions of high-frequency cycles.
Plies: The body plies constitute the tire’s basic skeletal structure. Plies are usually composed of polyester or other fiber cords wound together and sandwiched in rubber as well. Radial plies all run perpendicular to the direction of the tire’s spin, and it is this pattern that gives a “radial” tire its name, as opposed to “bias-ply” tires in which the plies are placed at overlapping angles. Fiber cords are used because they are quite flexible, but inelastic, that is, they do not stretch. Thus they allow the tire to flex but keep it from deforming or losing shape under pressure. Plies can be damaged or cut, usually by a sharp impact. When that happens, the rubber becomes unable to resist high air pressures
and begins to “bubble out.