Ian Jones, a vehicle dynamics engineer, believes it's because of what he says is the Explorer's dangerous tendency to flip.
"If you have a tall, narrow vehicle, it's gonna be very unstable. And so you, in effect, create the rollover situation because of the tire failure."
Ford lawyers are concerned about "a significant chance of failing" a consumer rollover test, wrote the head of the Explorer test program. "I believe...management is aware of the potential risk with P235 tires and has accepted the risk."
Ford admits its engineers were "worried," but says a single document is meaningless.
"In those tens of thousands or hundreds of thousands of pages that we produce, can I pull out one page where some engineer is worried about whether he is going to make it? You bet...But you have to look at the totality," said Ford Vice President Helen Petrauskas.
Ford changed the Explorer's suspension in 1995, but the very next year, there was an unexpected rollover on Ford's own test track-- and with professional drivers. The Explorer did pass a Consumer Reports rollover test in 1997. But the following year there were two more rollovers on Ford's test tracks. One was so unexpected the driver was not even wearing a helmet.
Rollovers were of such concern, says attorney Tab Turner, Ford dropped the recommended tire pressure for Explorers several years ago.
"One of the advere consequences of dropping your tire pressure from say 32 psi down to 26 28 psi is the fact that the tire is going to naturally run hotter-- the more likely it is to fail," said Turner, who is representing victims in legal action against Firestone and Ford.
The first lawsuits alleging that Firestone's tires suddenly lost their tread were filed nearly a decade ago.
But the National Highway Safety Administration only began its investigation into the safety of the tires in May. And that was almost a year after Ford replaced the firm's tires on its vehicles in parts of Latin America, Asia and the Middle East.
Critics say the case illustrates a fundamental problem with the federal agency's responsible for auto safety: NHTSA largely depends on manufacturers to police themselves and notify it when problems are uncovered.
"This has been going on for some number of years and the company (Firestone) never notified the agency, and that to me suggests a failure in the agency's program," said Joan Claybrook, president of watchdog group Public Citizen and a former director of NHTSA.
NHTSA officials also say Ford did not tell them about the recalls in Venezuela, Ecuador, Thailand, Malaysia, Colombia and Saudi Arabia, Egypt, Jordan, Kuwait, Lebanon and other Middle Eastern countries.
Ford spokesman Mike Vaughn said the Middle Eastern recall started in August 1999, followed by Malaysia and Thailand in February and the South American countries in May.
Vaughn said there were many reports of tread separation on vehicles in those countries. He said Ford officials did not report it to NHTSA because they didn't see the same problem in the United States and attributed it to different environmental and usage patterns.
"It's very hot, people in these markets tend to drive very fast, full-throttle, for extended periods. We also saw poor repairs and overloading,'' he said. "In the United States, you don't see the same usage patterns."
Transportation Secretary Rodney Slater said NHTSA "should have known about the recalls in other countries," but he resisted criticizing Ford or Bridgestone/Firestone for not coming forward earlier. He said NHTSA must work with manufacturers to protect citizens and the "blame game" would hinder those efforts.
Some safety experts say NHTSA isn't to blame, but that Congress needs to grant the agency greater authority.
"NHTSA's doing as good a job as the authority and the weak teeth that they have," said Clarence Ditlow, director of the Center for Auto Safety. "They can only do what Congress gives them the authority to do."
Congressional staffers visited Ford Motor Co.'s headquarters on Friday to investigate when the automaker may have known there was a problem with some Firestone tires.
In addition, House Commerce Committee Chairman Tom Bliley, R-Va., announced Friday that four panel staffers would meet with Bridgestone/Firestone Incofficials Monday at the company's headquarters in Nashville, Tenn.
"This is an ongoing search to find the truth of what they knew and how long they knew it," said a Commerce Committee spokesman.
The House committee will hold a hearing next month on the recall, although no date has been set yet.
For its part, the Senate Commerce Committee has scheduled a hearing for Sept. 6 to investigate the events leading up to the recall, how the industry reports to federal regulators and whether additional legislation or funding is needed.
Ford Chief Executive Officer Jacques Nasser, Firestone Executive Vice President John Lampe and NHTSA Administrator Sue Bailey have been asked to testify before the Senate committee along with representatives of consumer groups.
Despite calls to include more tires, a NHTSA spokesman dismissed as premature the notion that it is moving toward expanding Firestone's recall of 6.5 million tires.
"We're still very much involved in investigation and we have not reached any conclusions -- don't even have any instincts" yet on whether a widened recall may be necessary, NHTSA spokesman Rae Tyson said.
Correspondent Attkisson says Slater told reporters Friday he was urging Firestone to widen the recall, but called later to say he didn't mean it and that so far there is no evidence to warrant expansion.
About 900,000 Firestone ATX, ATX II And Wilderness AT tires have been replaced so faralmost 14 percent of the total recall -- but investigators are looking into the safety of almost 47 million tires.