Which of the following is a cause of tire fires?

Under inflation is a significant cause of tire fires due to the increased heat generated by a tire that is not properly inflated. When tires are under inflated, they flex more than normal as they rotate, which creates additional friction and heat buildup. This excessive heat can lead to a failure of the tire, which can ignite materials surrounding the tire or even lead to the tire itself catching fire.

Proper tire inflation ensures even weight distribution on the tire surface, reduces friction, and maintains optimal temperature levels. Maintaining the correct air pressure is crucial not only for wear and performance but also for safety. In contrast, over inflation, excessive speed, and lack of tread can contribute to other types of tire wear or blowouts, but they do not directly lead to the same risk of ignition and fire as under inflation does.