21.   Those came as standard equipment on many Ford Explorers, which have experienced catastrophic accidents involving tire failure, and some other SUVs and pickups.

22.   Tire failure in an Explorer may be a bigger problem than in other vehicles, said David A. Champion, the director of auto testing for Consumer Reports magazine.

23.   Tire failure is generally caused by overheating, Bozarth said.

24.   Underinflation is the leading cause of tire failure.

25.   Tread separations are the most common form of tire failure, yet the separations have proved to be unusually deadly on Explorers.

26.   Whether overloading played a role in the Firestone tire failures is not clear.

27.   Why have the recent tire failures been unusually deadly?

28.   All of those factors increased the likelihood of cracking, blistering and tread separations that would cause complete tire failures, according to the analysis.

29.   And Firestone still insists that the lower inflation pressure recommended by Ford Motor Co. played a role in the tire failures.

30.   Both companies have analyzed the tire failure.