Cause of Tire Failures Still a Matter of Dispute


More than two months into the recall of 6.5 million tires linked to scores of fatal accidents, Bridgestone/Firestone Inc.'s investigation into the cause of the failures has zeroed in on fatigue cracks that form in the rubber between the steel belts and then spread throughout the tires.

But it’s still anyone’s guess what might be causing those cracks in the first place--manufacturing flaws, poor design or improper tire inflation and maintenance. The root cause of the sudden tread separations that are linked to 119 deaths in this country and dozens more overseas remains a source of mystery and controversy.

There is not even agreement whether the main culprit is the failing tires or the sport-utility vehicles that roll over after blowouts, often killing or injuring their occupants.

That’s a worrisome thought, given the possibility that some SUVs equipped with certain tires not included in the recall might be, in effect, rolling time bombs.

Ford Motor Co. and Firestone have not reached any conclusion as to why the tires failed, prompting the Aug. 9 recall. They say they are working night and day to determine the reasons for the tire failures, most of which happened on Ford Explorers.


“We have not gotten to the point where there’s anything definitive to report yet,” Ford spokesman Jon Harmon said. Ford has steadfastly maintained that whatever the cause is, it’s a tire problem, not a vehicle problem.

The only word from Firestone came last week from Sanjay Govindjee, an associate professor in UC Berkeley’s civil and environmental engineering department who was brought in by the tire company to conduct an independent investigation.

Govindjee said in a memo to Firestone that he is focusing on fatigue-induced internal cracks that spread between the two steel belts. “At some stage the cracks reach a critical size and the tires subsequently fail,” Govindjee said.

The failure in this case is tread separation, or more correctly, belt separation. Tires tend to come apart between the two steel belts because that is the area subjected to the greatest stress.

Some tire experts say it is important not to rule out the most obvious cause: tire punctures from sharp objects in the road such as glass, rocks or pieces of metal. “The vast majority of tire failures are due to road hazards,” said Harold Herzlich, an independent tire consultant based in Las Vegas. “You’re dealing with a rubber object retaining air, holding up a 4,000-pound missile. These impacts are ballistic.”

Encounters with sharp objects can leave a gash, causing instantaneous deflation of the tire or small lacerations or punctures that allow air or water under the tire’s surface. There can be internal damage in the tire, causing a tiny area of separation that could continue to grow for 5,000 miles before the tire fails.

Although this accounts for a large number of highway tire failures, it nonetheless doesn’t explain why treads have been coming off primarily on Ford Explorers equipped with certain Firestone tires.

John Lampe, chief executive of Nashville-based Bridgestone/Firestone, a subsidiary of Japan’s Bridgestone Corp., made clear in testimony before Congress and in public statements that he believes Ford is partially responsible for the automotive industry’s biggest liability crisis.

“In most cases a vehicle that experiences a tire failure can be brought safely under control,” Lampe told Congress last month. “However, we have seen an alarming number of serious accidents from rollovers of the Explorer after a tire failure.”

Experts say they think it’s a combination of the two.

“It’s definitely a tire and a vehicle issue. You’ve got the highly unstable vehicle and the tire that couldn’t handle the endurance that the consumer was expecting out of it,” said Keith Baumgardner, general manager of Tire Consultants in Georgia and a former retreader with Firestone.

Despite the lack of a conclusion, experts nonetheless have numerous theories as to what could be behind one of the biggest safety debacles in U.S. automotive history. The theories fall into four general categories: bad tire design, flaws in the manufacturing process, improper maintenance and design flaws in the Explorer itself.

Tire Design Flaws

Ford officials and plaintiff attorneys finger faulty tire design, whether in the tire’s weight, chemical compounds used in the rubber, the strength and composition of the steel belts, the compounds that go into the tread, the circular wedges that fit between the belts to help keep them in place or even the tread design.

There could be defects in the knit of the steel belts themselves, which are woven steel strands encased in a layer of rubber known as a skim coat. The skim coat itself could have insufficient gauge, or thickness, to allow proper bonding.

Govindjee, Bridgestone/Firestone’s outside investigator, wrote in his memo that he has found a slowly developing fatigue crack “that propagates through the belt wedge material and then subsequently into the belt skim between the steel belts.” He did not suggest, however, that this was a blanket defect, saying he needed more time to study the failed tires.

Tire experts have suggested the treads on the recalled tires are too wide, providing more surface area that contributes to heat buildup, a factor known to promote tire failure.

High temperatures leading to belt separation could also result from the low temperature resistance of the recalled tires, which were rated “C,” the lowest of three ratings, with “A” the most temperature-resistant. Each of the Explorer’s top 10 competitors, from the Jeep Grand Cherokee and Chevrolet Blazer to the Isuzu Rodeo and Mitsubishi Montero Sport, comes equipped with B-rated tires. Only the Toyota 4Runner offers a tire with a C rating with its entry-level package--but it also offers three other tires rated B.

Some critics say Firestone could have avoided, or at least greatly reduced, the separations by adding a nylon layer known as an overlay to cover the steel belts. This is usually done for high-speed-rated tires but also occasionally for puncture resistance, as the overlays stiffen the tire somewhat. Firestone’s tire made to Ford specifications for use in Venezuela included were supposed to have included nylon overlays (although when Ford examined tires sent back from Venezuela after accidents in that country it found that many lacked the layer).

But tire expert Herzlich says it is unlikely such a layer would have made a difference, in the U.S. or elsewhere. “Some say it would eliminate tread separations if you put them on all tires. That is simply not true,” he said. “An overlay gives only a very slight--and I say very slight--protection from penetrating road hazards . . . and will not eliminate tread separation due to under-inflation.”

Manufacturing Flaws

Defects can also be introduced in the manufacturing process through the use of substandard materials or ill-maintained workplaces; the introduction of contaminants, humidity or dryness; and improper vulcanization of the rubber.

The rubber in tires must be sticky enough to hold the pieces together until vulcanization welds the tire together. Under- and over-vulcanization are possible too; both weaken the tire’s structure.

Several experts say over-tacked rubber, or rubber that is too dry and has lost its adhesive character, is likely to be a major culprit in tire separation. “That’s the heart of the matter, the most damaging,” said Max Nonnamaker, a tire consultant in Ohio who has worked for Firestone and Mohawk Rubber Co.

Workers have been known to overproduce the coated steel belts and then stock the excess; if they sit in inventory too long, the rubber gets too dry and stiff to bend and bond properly. Tire workers have been known to use chemical solvents to make them stickier, but solvent not allowed to dry properly becomes a contaminant that prevents proper adhesion.

Alan Hogan, a former worker in Firestone’s Wilson, N.C., plant, testified in a deposition last year that he observed use of overly dry rubber “in the tire room the entire time between ’91 and ’94,” as well as improper application of solvents that could lead to tire separation.

He testified that he found a variety of contaminants in the rubber mixtures used to make tires, including bandages, cigarette butts, chewing tobacco, pieces of wood, and metal nuts and bolts.

In depositions from another lawsuit, four former workers at Firestone’s plant in Decatur, Ill., testified they used outdated, dried rubber; that solvents were not used properly, causing pockets of non-adhesion; that tires with defects commonly passed inspection; and that workers used awls to lance bubbles below the surface of tires.

“You should never, never awl anything,” Nonnamaker said. “You make a hole and hope it knits back together, but it may not, and you’re left with a hole in the tire.”

Bridgestone/Firestone dismisses the allegations as charges by disgruntled ex-workers. Ford’s Harmon said the auto maker is certainly “factoring in” what the former workers have to say.

Improper Maintenance

One theory given considerable credence by experts is that a low recommended tire inflation by Ford converged with something inherent in the tires and something inherent in the vehicle, effectively turning the recalled Firestones plus Ford Explorers into a deadly cocktail.

Running while under-inflated generates extremely high heat in tires, especially when they are carrying heavy loads, causing irreversible physical fatigue between the plies and deterioration in the tire’s material.

Ford always recommended an inflation of 26 pounds per square inch, while Firestone’s own recommendation was 30 psi. After the Aug. 9 tire recall, Ford recommended 26 to 30 psi, while Firestone held at 30.

In the end Firestone prevailed, persuading Ford to formally change its recommendation to a full 30 psi last month.

Generally, the industry considers inflation at 20% less than the recommended level to be dangerously low, said Ed Wagner, who runs the consultancy Tire Technical Services in Kentucky. Drivers, however, regularly reach that point.

“If it’s supposed to be 30 psi, and we’re riding at 24 psi with the same load, then you have gross under-inflation,” Wagner said. He and other experts say that if Explorers left the factory with their tires at 26 psi, by the time they got into customers’ driveways they were likely to be less than that, and given drivers’ ignorance or neglect, tire pressures probably continued to decrease.

Clarence Ditlow, head of the National Center for Auto Safety in Washington, said Ford’s 26-psi guidance was a “red flag,” because from that point, the only direction for tire pressure to go is down. “Then you have more heat buildup and more failures,” he said.

Both Ford and Firestone point to poor tire maintenance as a culprit in the accidents to date, pointing out that most Americans rarely check their tire pressure, though experts suggest tires be checked once a month.

Woody McMillin, a senior Bridgestone/Firestone spokesman for consumer products, said the tire maker has seen two factors emerge from its examinations of failed tires at its technical center in Akron, Ohio: improper care and extended periods of under-inflation.

“By and large, and most people don’t want to hear this, it’s poor maintenance of tires,” McMillin said. People basically don’t understand how tires work, he said, and that improper air pressure will weaken the sidewalls, much the way a piece of metal, when twisted, breaks at the weakened stress point.

Tab Turner, a Little Rock, Ark., attorney and a veteran in bringing liability lawsuits against auto and tire makers, scoffs at the idea that drivers are to blame. “What evidence is there that only Explorer owners are sloppy with maintenance?” he said. “If you have sloppy maintenance on six cars, and one of them is killing 90% of the people because the tire’s coming apart, that tells me there’s something wrong with that tire and that car.”

Explorer Stability

So there remains a vexing question: Why the Explorer? Critics charge that the Explorer, like many other SUVs, has a tendency to roll over, and they say that is why Ford recommended the lower inflation: A softer tire would keep the vehicle hugging the ground more.

Many suspect the Explorer is jinxed no matter how the tires are inflated: If too high, the vehicle has a propensity to tip over; if too low, the tires are prone to overheat and shred. “If someone has a flat tire on these Ford Explorers in the rear, I have seen them roll over,” said tire expert Baumgardner. “So we have a problem with the Ford rolling over no matter whose tire’s on it, but then we have the Firestone tire, which is designed for that vehicle and supplied for that vehicle that has exhibited these problems.”

As previously reported by The Times, Ford documents show that the auto maker rejected design changes twice in the last 10 years that would have made the Explorer more stable.

As the launch date for the truck drew near in 1989, designers declined to widen the Explorer’s track width, which would have delayed the launch, and instead lowered the vehicle by half an inch and stiffened the front springs. For the Explorer’s redesign in the 1995 model year, engineers considered lowering the center of gravity but chose not to, partly to save money and preserve high-profit margins, according to the documents.

Ford maintains those charges are based on only a few pages of technical opinions among tens of thousands of documents exchanged between engineers as they hashed out the design of a new vehicle.

“Then why don’t they single out one that says it’s safe?” said attorney Turner. “I haven’t seen one where an engineer wrote in 1989, ‘Oh, by the way, we don’t need to change the design of this car; this is the best car we’ve ever made.’ ”

According to Ford, crash data show the Explorer is 20% less likely to be involved in a fatal accident for any cause, or a rollover, than comparable SUVs and therefore is one of the safest SUVs on the road.

Ford is understandably mortified at the prospect that the Explorer might be blamed in part for the tire separations. The No. 2 auto maker clears at least $5,000 on each Explorer sold, and Explorers account for 25% of Ford’s profit.

Govindjee, the outside investigator, said the issue “is a quite complex interaction” of tire design and dynamics of the Explorer, though he stopped short of placing any blame on the vehicle.

He needs more time to inspect tires and field data, he wrote in his memo, but said he is confident he will be able to provide an explanation around the beginning of the year.


Firestone Tire Timeline

* March 12, 1999: An internal Ford Motor Co. memo says “Firestone legal has some major reservations” about replacing tires in Saudi Arabia after numerous accidents involving Firestone tires, notably that the U.S. Department of Transportation might have to be notified since the same products were sold in the U.S.

* Aug. 17, 1999: Ford begins replacing tires on Explorers in Saudi Arabia through what it calls a “customer notification enhancement action” and not a “recall.”

* February 2000: Ford offers free replacement tires for vehicles in Malaysia and Thailand.

* KHOU-TV in Houston first reports on significant numbers of deaths and lawsuits involving Firestone tires on Ford Explorers.

* March 6, 2000: The National Highway Traffic Safety Administration opens a preliminary inquiry after KHOU-TV programs prompt consumer complaints.

* May 2000: Ford offers free replacement tires for vehicles in Colombia, Ecuador and Venezuela.

* May 2, 2000: NHTSA opens a preliminary evaluation of the alleged failure of Firestone ATX, ATX II and Wilderness AT tires. Unknown to NHTSA, there are already lawsuits involving at least 35 fatalities and 130 injuries in the U.S.

* Aug. 2, 2000: NHTSA says it is investigating 21 deaths in crashes of pickup trucks and sport-utility vehicles in which tire failure may have played a role.

* Aug. 7, 2000: NHTSA raises to 46 the number of deaths associated with Firestone tires.

* Aug. 9, 2000: Bridgestone/Firestone announces the recall of 14.4 million tires, including all 15-inch Firestone ATX and ATX II tires, and 15-inch Wilderness AT tires made at its Decatur, Ill., plant. About 6.5 million are believed still in use.

* Aug. 31, 2000: Venezuela’s consumer protection agency, Indecu, asks prosecutors to bring criminal charges against both Bridgestone/Firestone Inc. and Ford.

* NHTSA raises to 88 the number of deaths associated with the Firestone tires.

* Sept. 1, 2000: NHTSA issues a consumer advisory on an additional 1.4 million Firestone tires, saying some of them have “high tread separation rates.” Firestone declines NHTSA’s request to expand the recall voluntarily to include the 1.4 million.

* Sept. 6, 2000: The Senate Appropriations Committee and the House subcommittee on consumer affairs conduct hearings on the tire recall. Bridgestone/Firestone executives claim for the first time in public that the Explorer has a tendency to roll over and is part of the problem.

* Oct. 10, 2000: John Lampe replaces Masatoshi Ono as Bridgestone/Firestone chief executive and says the recall is likely to cost parent company Bridgestone Corp. $450 million over the year.

* Oct. 11, 2000: Congress passes a sweeping auto safety bill that raises the maximum fines and adds criminal penalties for firms that deceive regulators about safety problems.

* Oct. 17, 2000: Bridgestone/Firestone says it will shut three plants temporarily and lay off 450 workers indefinitely.

* NHTSA raises to 119 the number of deaths in the U.S. associated with the Firestone tires.

* Oct. 18, 2000: Ford says the recall cost the auto maker half a billion dollars in the third quarter.

Sources: National Highway Traffic Safety Administration, House Commerce Committee, Tab Turner, Public Citizen, Times reports


Many Theories, No Answers

Two months into the recall of 6.5 million Firestone tires, investigators still don’t know the cause of the blowouts. The theories that have been proposed fall into four main categories.


Design Flaws

* Poor rubber quality

* Composition (steel belts improperly spliced together)

* Tire treads too wide

* Low temperature resistance

* Lack of nylon overlay


Manufacturing Flaws

* Over- or under-vulcanized rubber

* Using overly dry rubber

* Misuse of solvent

* Humidity and moisture (water, rain, perspiration)

* Contaminants (dust, oil, bandages, cigarette butts, tobacco juice, candy wrappers, etc.)


Poor Maintenance

* Under-inflation

* Running tires at high speeds, temperatures for prolonged periods


Explorer Stability

* Center of gravity too high

* Track width too narrow

* Badly designed suspension

Source: Times research