NHTSA investigating failure of Firestone brand tires

More complaints from hot-weather areas

The majority of the complaints about the tires have come from hot-weather states including Texas, California and Florida, although Michigan, Pennsylvania and Ohio also have filed complaints with the agency. Investigators are not sure if warm weather is a factor in the potential product problems, but they are including it in the investigation.

Just Thursday, the Florida Highway Patrol told CNN the tread of a Firestone AT tire separated on a sport utility vehicle, causing the vehicle to roll over three times on a median on Interstate 75, ejecting four of the vehicle's five occupants. The accident will be reported to the NHTSA, and "hopefully they will push to find out whether this is truly a bad product," said highway patrol Lt. John Bagnardi.

Earlier this week, two Florida families sued Ford Motor Co. and Bridgestone/Firestone. The families maintain that the tire tread on their Ford Explorers separated, causing fatal accidents.

Similar suits concerning the tires have been filed since 1996.

Investigation could bring recall

The NHTSA's preliminary evaluation is the first in a three-step process. If there is evidence of possible defects in the product, the agency will conduct an engineering analysis. Those findings will determine if there is sufficient evidence to issue a recall.

A recall is issued only if there is a definite trend in product failure.

Firestone's parent company, Nashville, Tennessee-based Bridgestone/Firestone, said in a statement this week that it has full confidence in its tires, of which almost 48 million have been made.

The company said it is offering free tire inspections in light of safety concerns.

"We will inspect the tire for damage or excessive wear and ensure the tires are inflated to the level specified by the vehicle's manufacturer," said spokeswoman Christine Karbowiak. "If there is a problem, we will remedy the situation to the customer's satisfaction."

Ford replaced tires in six other countries

Ford has been investigating reported problems with the tires since May, company spokeswoman Jerree Martin said.

Ford has replaced Firestone tires for free on vehicles sold in Venezuela, Ecuador, Thailand, Malaysia, Colombia and Saudi Arabia after tires failed in those countries. Though not accepting blame, Ford said it swapped tires "as a customer satisfaction issue." It has not made a decision on replacing tires for U.S. customers.

The tires have been original equipment on Ford, General Motors, Toyota, Nissan and Subaru vehicles for several years, but most accidents reported to the traffic safety agency have involved the Ford Explorer.

Safety administration spokesman Tim Hurd said Wednesday the agency does not yet know why so many of the incidents have been on Explorers.

He said 28 reports of tread separation noted that the tire remained inflated, sometimes even after a crash. He said that in two cases, the tire tread wrapped around the rear axle and locked up the wheels.

Tread failure was reported at a speed of 20 mph, but 55 to 75 mph was typical. Some tires that failed had less than 2,000 miles of use, the agency's records show.