NHTSA Announces Initial Decision That Additional Firestone Wilderness AT Tires Have a Safety Defect; Firestone Agrees to Recall Those Tires

Topics:  Firestone

NHTSA
October 4, 2001

NHTSA 51-01
Thursday, October 4, 2001
Contact: Rae Tyson
Tel. No.: (202) 366-9550

The U.S. Department of Transportation's National Highway Traffic Safety Administration (NHTSA) today announced its initial decision that a defect related to motor vehicle safety exists in certain Firestone Wilderness AT tires installed on sport utility vehicles (SUVs). These tires are sizes P235/75R15 and P255/70R16 manufactured by Firestone prior to May 1998 that were either supplied to Ford Motor Company (Ford) as original equipment or were sold as replacement tires.

Firestone has told NHTSA that, rather than contesting the decision, it will recall the tires. In addition, the company says its dealers will offer to replace, at no cost to consumers, these sizes of Wilderness AT tires that are installed on pickup trucks.

"The American public is well served by removing defective products from the road without delay," said Dr. Jeffrey W. Runge, the NHTSA Administrator. "We are pleased that Firestone has taken this approach in lieu of lengthy court proceedings, moving us quickly to a safe solution."

Firestone produced an estimated 3.5 million of these Wilderness AT tires. They were primarily used as original equipment on Ford Explorer and Mercury Mountaineer SUVs, to a lesser extent as original equipment on Ford Ranger compact pickup trucks, and as replacement tires on these vehicles and others.

In August 2000, Firestone determined that a safety-related defect existed in all Firestone P235/75R15 ATX tires and in Wilderness AT tires of that size manufactured at its Decatur, Illinois plant, and recalled those tires. NHTSA's Office of Defects Investigation (ODI) has conducted an extensive investigation to determine whether other Wilderness tires, beyond those recalled by Firestone, contain a safety-related defect, and whether they should be recalled.

NHTSA's initial decision applies only to P235/75R15 and P255/70R16 Wilderness AT tires of the design supplied to Ford as original equipment. It does not apply to other tire sizes of Wilderness AT tires, such as those supplied by Firestone to General Motors and Toyota as original equipment, since those tires have different design features and have experienced relatively few tread separations.

Most of the tires subject to today's NHTSA decision were manufactured at Firestone's Wilson, North Carolina and Joliette, Quebec, Canada plants. Fewer than 100,000 of these tires, in the P235/75R15 size, were produced at the company's Oklahoma City plant. Tread separation failures on the Wilderness AT tires covered by NHTSA's initial decision have led to numerous claims and crashes, approximately 50 injuries, and 25 reported fatalities. Although these figures are lower than those for the recalled ATX tires, this is because the Wilderness AT tires have not been in service as long. Plant-by-plant failure trends for these tires are very similar to those of the recalled ATX tires over similar periods of service. Their failure rate is also significantly higher than that of competitors' tires used on SUVs, especially the Goodyear tires used as original equipment on the Ford Explorer.

The tread separations at issue in this investigation reduce the ability of a driver to control the vehicle, particularly where the failure occurs on a rear tire and at high speeds, and can lead to a crash. The likelihood of such a crash, and of injuries or fatalities, is far greater when the tread separation occurs on an SUV than when it occurs on a pickup truck. Claims and complaint data indicate that a tread separation on an Explorer is no more likely to lead to a crash than on other SUVs.

Like other radial tires, the Wilderness AT tires have two steel belts. Tread separations typically begin as belt-edge separation at the edge of the top belt, the area of highest strain in a steel-belted radial tire. Once belt-edge separations begin, they can grow and develop into cracks between the belts. If they grow large enough, they can result in catastrophic tread detachment, particularly at high speeds.

In these Wilderness AT tires, the design of the "shoulder pocket" can cause higher stresses at the tire's belt edge. The tires often exhibit a series of weak spots around their circumference, leading to the initiation and growth of cracks earlier than in competitors' tires and in other Firestone tires used on light trucks.

A critical design feature used by tire manufacturers to suppress the initiation and growth of belt-edge cracks is the "belt wedge," a strip of rubber located between the two belts near their edges on each side of the tire. The belt wedge thickness in the ATX and these Wilderness AT tires produced prior to May 1998 is typically less than those of competitors' tires. These tires did not adequately resist the initiation and growth of cracks between the steel belts.

During March and April 1998, Firestone phased in a thicker wedge gauge, which then became comparable to competitors' tires, and revised its material composition. These modifications would tend to inhibit the initiation and spread of the belt-edge cracks that lead to tread separations. Moreover, there have been very few tread separation failures of the tires with the improved wedge, and NHTSA's inspection of used Firestone tires indicates that these tires have less severe cracks and separations between the belts than tires built before these changes.

For these reasons, NHTSA did not include the tires with the improved belt wedge in its initial defect determination. However, because tread separation failures rarely occur in these tires until at least three years of use, NHTSA cannot determine whether their actual field performance is significantly better than the older tires. NHTSA will continue to monitor the field performance of these newer tires.

On May 22, 2001, Ford announced a program to replace all Wilderness AT tires installed on its vehicles. NHTSA encourages owners of all Ford vehicles with P235/75R15 and P255/70R16 Wilderness AT tires built after April 1998 to take advantage of the Ford program.

The rate of tread separation failures of Wilderness AT tires on Ranger pickup trucks is lower than their failure rate on Explorer SUVs. This is due to a variety of reasons, including the fact that the Explorer generally carries higher loads, and its tires had a significantly lower recommended inflation pressure, particularly on the rear wheels. Moreover, the likelihood of a crash due to a tread separation, and of deaths or injuries, is substantially lower on a pickup than on an SUV. Therefore, NHTSA's initial decision applies only to tires installed on SUVs. However, because the risk of future separations on pickup truck tires remain a cause for possible concern, NHTSA is pleased that Firestone will offer to replace these tires on pickup trucks at no cost to owners.

Consumers with P235/75R15 and P255/70R16 Wilderness AT tires can determine whether their tires are covered by this action by checking the DOT serial number on the tires, which is located in the lower sidewall area directly above the rim flange. The tires are covered if the last number is "4," "5," "6," or "7." If the last number is "8," only those tires having 018 through 188 as the last three digits are included. Firestone dealers and retailers will also provide assistance in this regard.

Engineering Analysis Report and Initial Decision Regarding EA00-023: Firestone Wilderness AT Tires