Firestone Blames Design, Process, Ford

WASHINGTON--After initially blaming consumers for poor tire maintenance practices for a rash of fatal tread separation crashes, Bridgestone/Firestone Inc. now says a faulty design and aspects of the manufacturing processes at its Decatur, Ill., plant are responsible for the problems. The company also cited the design of the Ford Explorer as a cause.

Ford maintains that the Explorer is not to blame, although it did replace Explorer suspensions--while charging customers for the modifications--in Venezuela. Ford has maintained that “It is absolutely incorrect to assert that the design of the Explorer is contributing, in any way, to this serious safety problem. We have made stiffer shock absorbers available to our customers in Venezuela to address ide quality complaints related to washboard road surfaces,” according to Helen Petrauskas, Ford’s vice president of environmental and safety engineering. Ford said it has not had tire trouble with Goodyear-equipped Explorers

Samuel Ruh Rios, head of the Venezuelan consumer protection agency, has said that the crashes resulted from “a lethal combination” of the Explorer’s design and certain Firestone tires. He said the wrecks “have been caused by a macabre combination between a suspension that is set too soft and tires that are not appropriate for the Explorer.”

The Washington Post said in August that, according to a Ford document obtained by congressional investigators, the company’s own analysis of rollovers after tire explosions in Venezuela found the problem unique to the Explorer. “High incidence of vehicle roll-over after a tire blow out or tread loss has not been detected for other vehicle brands,” such as Toyota Motor Corp., General Motors Corp. and Chrysler Corp., the document said as reported by the Post.

In the wake of 148 U.S. deaths linked by the government to Firestone tires, Firestone’s four-month investigation cites the shoulder design of the 15-inch ATX tires and the unique way the rubber was processed at Decatur.

Firestone says another factor was the lower inflation pressure and higher vehicle load limits recommended by Ford, which the automaker and consumer safety advocates continue to contest.

“Our team’s findings confirm what the initial statistical claims information demonstrated from the outset-- that a small number of tires generated higher rates of tread separation claims when used on Ford Explorers and that our recall initiated in August was more than adequate to protect the public,” said Bridgestone/Firestone Chairman and Chief Executive Officer John Lampe.

The factors Firestone cited behind the tire failures are:

•The shoulder pocket design of P235/75R15 ATX tires could lead to cracking at the shoulder pocket bottom. This could become the starting point of a failure, which when combined with the other factors result in a reduction of resistance against belt detachment.

• Low inflation pressure in the recalled ATX, ATXII and Wilderness AT tires increased the running temperature of tires and would contribute to a decreased belt adhesion level.

• Vehicle load levels and low standard tire pressure initially specified for the primary vehicle for which the tires were designed led to a decreased margin of safety for tire performance.

• ATX P235/75R15 tires and Wilderness AT tires of the same size produced at Decatur exhibited different belt adhesion characteristics, including lower initial adhesion, than those same size and line tires produced at other Firestone plants.

“These factors the team has identified, when working in concert, are the major causes for why some P235/75R15 ATX, ATXII and Decatur-produced Wilderness AT tires experienced an increased rate of tread separation,” said Lampe. He emphasized that tire care issues carry a lot of the load in assessing the fatal crashes. “Tire industry experience demonstrates that many tread separations can be caused by various forms of tire damage encountered in daily use, such as punctures, improper repairs, severe impacts or being misapplied. Many of the reported incidents are attributable to these factors, and not those identified in the company’s root cause investigation. This was one of the difficulties the team encountered in conducting our analysis,” he said.

The P235/75R15 ATX and ATXII tires are no longer in production. The tread of the Wilderness AT line of tires, which replaced the ATX II as original equipment on the Ford Explorer in 1996, is significantly different from the ATX and ATXII tires. The Wilderness AT was introduced with a new tread design as part of the ‘96 redesigned Explorer.

“Although the skim stock, a rubber coating surrounding the steel belts, from Decatur was within specifications, Firestone is implementing changes to the processing of skim stock at Decatur so that its physical properties will be equivalent to that of the other Firestone plants before it begins using that material again,” said Lampe.

According to a dispatch by the Associated Press, 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, said two sources familiar with the briefings who spoke to the AP 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 AP said, citing its unidentified sources.

Firestone has also brought in an independent expert, Dr. Sanjay Govindjee, to conduct his own review, the results of which are expected later this month.

Firestone said that when the National Highway Traffic and Safety Administration (NHTSA) and Ford review the materials they will agree with the company’s findings.

In addition, Lampe said, the company is implementing the findings of a special internal Comprehensive Quality Review team, comprised of technical, engineering and safety professionals. This team reviewed the overall tire manufacturing and data collection systems within the company, focusing on production operations, tire enhancements and quality assurance. “The team members have completed their review and Bridgestone/Firestone is putting their recommendations into practice,” Lampe said.