Both companies provided their "root cause" analyses, basically supporting their previous theories as to what's to blame, focusing on an unusual combination of factors from flawed designs to manufacturing problems at Firestone's Decatur, Illinois plant.
But they differ on whether Ford shares in the blame, reports CBS News Correspondent Sharyl Attkisson. Firestone says Ford does in part for its Explorer design, which is allegedly prone to flipping over, leading to so many of the deaths under investigation.
After a four-month government investigation, the Nashville-based tire maker cited the shoulder design of the 15-inch ATX tires and the unique way the rubber was processed at Decatur. In the report, Bridgestone/Firestone said another factor was the lower inflation pressure and higher vehicle load limits recommended by Ford.
Ford Motor Co. on Tuesday said its own data mostly concur with the Bridgestone/Firestone report, but also defended the safety of its Explorer.
NHTSA links 148 deaths and more than 525 injuries in the United States to separations, blowouts and other tread problems in Firestone's ATX, ATX II and Wilderness AT tires, 6.5 million of which were recalled during the summer, many made at the Decatur plant. Many of the tires were standard equipment on the Ford Explorer.
Ford and Bridgestone/Firestone officials briefed NHTSA on the status of the investigation last week. Bridgestone/Firestone officials met Monday with congressional investigators, while Ford officials were to meet with them Thursday.
Attkisson reports the federal investigation into the tire problems still has several months to go. One holdup has been difficulty in finding independent experts and independent labs to conduct tests on tires.
Exclusive video obtained by CBS News offers a dramatic glimpse of the most violent reaction possible to a tread separation. The tests were conducted for lawyers suing Ford.
In the test, the Explorer is fitted with a special outrigger to keep from flipping over. At the moment the tire tread separates, the Explorer appears to swerve drastically out of control. Then something completely unexpected happens: the protective outrigger breaks and the Explorer rolls over.
"The response can be very violent," says Mark Arndt, of Transportation Safety Technologies. "In fact, the response can be so violent, as in this test, that it's not controllable. And I was very surprised to find out how uncontrolled the response of the vehicle was."
There have been calls for more tires to be recalled, but Bridgestone/Firestone said its research shows that its August recall of 6.5 million tires is sufficient.
Bridgestone/Firestone Chairman John Lampe said in statement that the findings show that "our recall initiated in August was more than adequatto protect the public."
The company's recall, which began in August, is one of the largest in U.S. history. The tire problems have been subject to high-profile congressional hearings and investigation and prompted Congress to pass an overhaul of U.S. tire safety regulations.
As reports of traffic deaths mounted over the summer, the company was unable to explain why so many tires came apart on the road.
The report backs up the company's contention that the problem is concentrated in Decatur.
The current recall is concentrated on though not limited to tires made in Decatur.
In its report, Bridgestone/Firestone blames the failures on a combination of four factors, including
- The shoulder design of the 15-inch ATX tires, which can lead to cracking and belt detachment;
- Different belt adhesion characteristics of tires built in Decatur compared to other plants;
- Low inflation pressure in the recalled tires that would increase the running temperature of the tires and contribute to decreased belt adhesion; and
- Vehicle load levels specified for the Explorer.
Ford said Firestone's tire design and problems at the tire maker's Decatur plant contributed to tire failure. But Ford also said independent data found its Explorer was safe.
"In our discussions with both NTHSA and Firestone we discussed tire design and manufacturing problems, and we still don't see the Explorer as the issue," Ford spokesman Ken Zino said.
He said the Explorer's weight has not changed significantly.
The Decatur plant uses a process known as pelletizing, where rubber pellets are blended with a lubricant to create the rubber that coats the steel belts of the tire, according to two sources familiar with the briefings who spoke to the Associated Press on a condition of anonymity.
This process is unique to Decatur. Other plants use a slab system that does not involve pellets.
The lubricant apparently causes a breakdown in the tire that can cause separation of the tread, the sources said.
Lampe said in the statement that the company is changing its manufacturing processes in Decatur so that it matches the other plants.
But the vice president of the United Steelworkers local 713 at the Decatur plant said it isn't fair to drop the whole problem on the doorstep of one factory.
"I feel like they're questioning our workmanship," Harland Smith said. "We have tires out there with 80,000 miles on them...We have workers at our plant that drive on them same tires and never took them in for the recall."
Smith believes the tire failures more likely came from overall design problems and more significantly from the lower inflation pressure recommended by Ford.
"Underinflating the tires puts more heat and stress on them,"Smith said. "Most of the failures happened in hot states down south."
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