What is one cause of tire fires?

Under-inflated tires are a significant cause of tire fires because when tires are not inflated to the proper pressure, they can overheat. This overheating occurs due to increased friction between the tire and the road surface, as well as the tire's own structural components working harder to maintain their shape. The excessive heat generated can lead to the breakdown of the tire material, ultimately causing a fire if conditions are right.

In contrast, excessive speed may contribute to tire failure or blowouts but does not directly lead to tire fires as under-inflation does. Similarly, while excessive tread wear can compromise tire integrity and increase the likelihood of blowouts, it does not have the same overheating risk associated with under-inflation. High-quality tires, on the other hand, are typically designed to withstand higher pressures and heat, making them less likely to catch fire compared to poorly maintained or low-quality options. Thus, the link between under-inflated tires and the potential for tire fires makes it the most pertinent answer.