The bead is a rigid hoop of steel braid, with the inner free edges of the plies wrapped around it. It must be rigid, to keep the tire on the rim, but soft enough to seal the air in the tire.
A cross-ply tire has a latticed, criss-crossed structure, with alternate plies crossing over each other, and laid with the cord angles in opposite directions.
Manufacturers use a sophisticated selection process to create combinations that provide the required performance characteristics and 'hysteresis level' of the tire. Having fewer plies makes a tire more flexible. Higher numbers of plies make its response to bumps harsher.
Aspect ratio is included in the sidewall marking, with the type of construction, and the speed rating. Metric-diameter rims cannot be fitted with imperial-diameter tires, or vice-versa.
