Defective Firestone Tire Treads

Firestone Tire Tread Defects:
Hundreds of motor vehicle accidents resulting in death or serious injury, were caused by tire tread or belt "separation" from defective Firestone tires.

Study of Firestone Tires

The National Highway Traffic Safety Administration tasked their Office of Defects Investigation, or ODI for short, with expanding their investigation of defective tires. The focus of the ODI's research was on those non-recalled tires that are similar to the recalled Firestone tires (i.e., Wilderness AT tires of the size P235/75R15 and P255/70R16 manufactured by Firestone for supply to Ford Motor Company as original equipment), as well as replacement tires manufactured to the same specifications ("focus tires").

Most of the focus tires were manufactured at Firestone's Wilson, North Carolina and Joliette, Quebec plants, beginning in 1994. In late 1998, Firestone began producing P255/70R16 Wilderness AT tires at Decatur, and in mid-1999, it began producing P235/75R15 Wilderness AT tires at a new plant in Aiken, South Carolina. Also, approximately 100,000 P235/75R15 Wilderness AT tires were produced at Firestone's Oklahoma City, Oklahoma plant. The focus tires were predominantly used as original equipment on Ford Explorer SUVs and, to a lesser extent, on Ford Ranger compact pickup trucks, and as replacement tires for use on these and other SUVs and pickups.

The belt-leaving-belt tread separations that have occurred, and are continuing to occur, in the recalled and focus tires begin as belt edge separation at the edge of the second, or top, belt. This is the area of highest strain in a steel belted radial tire and it is also a region with relatively poor cord-to-rubber adhesion because bare steel is exposed at the cut ends of the cords. Once belt-edge separations have initiated, they can grow circumferentially and laterally along the edge of the second belt and develop into cracks between the belts. If they grow large enough, they can result in catastrophic tread detachment, particularly at high speeds when the centrifugal forces acting on the tire are at their greatest.

Non-destructive analysis tests were performed on numerous randomly collected focus tires and peer tires from the southern states, where most of the tire failures have occurred. The non-destructive analysis tests use shearography, which can detect separations inside a tire. Shearography analysis tests demonstrated that the patterns and levels of cracks and separations between the belts were far more severe in the focus tires than in the peer tires. Many of the focus tires that were examined were in the later stages of failure progression prior to complete separation of the upper belt.

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 the belt edges on each side of the tire. The belt wedge thickness, or gauge, in the Firestone ATX tires and the Wilderness AT tires produced prior to May 1998 is generally narrower than the wedge gauge in peer tires, and the wedge gauge in cured tires was often less than Firestone's target for this dimension. The Firestone tires with this narrow wedge did not adequately resist the initiation and propagation of belt-edge cracks between the steel belts. During March and April of 1998, Firestone changed the material composition and increased the gauge of the wedge in its Wilderness AT tires (and some other tire models).

Another important feature of radial tires related to the prevention of belt-leaving-belt separations is the gauge of the rubber between the two steel belts, or "inter-belt gauge." The inter-belt gauge initially specified by Firestone for the focus tires is generally narrower than the inter-belt gauges in peer tires and is narrower than Firestone's original specification for the ATX tires in the early 1990s. Moreover, the actual measured gauge under the tread grooves in several of the focus tires measured by ODI was far less than Firestone's minimum design specification. Since an inadequate inter-belt gauge reduces the tire's resistance to crack growth and its belt adhesion capabilities, this narrow inter-belt gauge may be partially responsible for the relatively low peel adhesion properties of the focus tires compared to peer tires. In August 1999, after becoming concerned about the adequacy of the inter-belt gauge in the cured Wilderness AT tires, especially in the regions directly under the tread grooves, Firestone changed the inter-belt gauge specification back to the original dimension.

Another relevant feature is the design of the shoulder pocket of the focus tires. The shoulder pocket design caused higher stresses at the belt edge and lead to a narrowing, or "pinching," of the wedge gauge at the pocket. The focus tires exhibit a series of weak spots around the tire's circumference, leading to the initiation and growth of cracks earlier than in competitor tires and in other Firestone tires produced for light trucks and SUVs. In addition, many of the focus tires exhibited shoulder pocket cracking similar to that which Firestone identified as a significant contributor to the risk of tread detachment in the recalled ATX tires.

Because the tread separations at issue in this investigation occur only after several years of exposure, almost all of the tire failures on which the Office of Defects Investigation analysis of field experience was based involved tires manufactured before May 1998, when Firestone increased the dimensions and improved the material of the belt wedge. In theory, these modifications to the wedge would tend to inhibit the initiation and propagation of the belt-edge cracks that lead to tread separations. If these modifications actually improved the resistance of the focus tires to belt-edge separations, the historical failure trends described above may not predict the future performance of the newer tires.

On the basis of the information developed during the ODI investigation, NHTSA made an initial decision that a safety-related defect exists in Firestone Wilderness AT P235/75R15 and P255/70R16 tires manufactured to the Ford specifications prior to May 1998 that are installed on SUVs. These tires were manufactured primarily at Wilson and Joliette and, to a lesser extent, at Oklahoma City. The initial decision does not apply to the P255/70R16 tires produced at Decatur or any of the Wilderness AT tires produced at Aiken, since these tires were all manufactured after May 1998.

Tire Defects - Serious Accident and Injury Legal Help

If you or a loved one have been seriously injured, or a loved one has been killed, as the result of a tire defect, tire failure, tread separation, tire blowout, rollover accident, or any other serious injury accident, then please call us to discuss your legal rights to a potential product liability lawsuit. Please fill out our online form by following the link below or call us right now: Toll Free 1-800-883-9858.

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