As tire deflection increases from the slow but steady decrease in inflation pressure, an extreme over-heating occurs, especially at the fold in the sidewall. Temperatures can reach over 400 F, the melting point of the polyester cords typically used in the radial plies. Destruction of the sidewall is then quick and massive. There are other causes besides punctures for an unexpected loss of inflation pressure. Valves can leak.
Rims can bend or corrode, resulting in a failure of the air seal between the tire bead and rim.
In addition, tires lose about 1 psi per month via normal permeation. Under normal loads and pressures, within self-imposed limits of operating speed, and remaining free of road hazards, a tire is expected to hold together until the tread wears out. Should this speed rating be exceeded, the tire will typically fail via a separation at the belt edges. Furthermore, all tires have virtually the same sensitivity to load and inflation pressure, as shown in figures 2 and 3. As the temperature at the belt edges increases with increasing speed, it reaches a point which, when combined with the centrifugal and other forces, causes a loss of adhesion and a tearing of the rubber.