Re: Tire guru please! Questions on tire mileage
NOSLEEP - no offense, but the independent engineering analysis says otherwise:<br /><br />ODI conducted a non-destructive analysis of numerous randomly collected focus tires and peer tires from southern states, where most of the failures have occurred, using shearography, which can detect separations inside a tire. This shearography analysis demonstrated that the patterns and levels of cracks and separations between the belts were far more severe in the focus tires than in 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. The shearography results for tires manufactured at Wilson were similar to those manufactured at Joliette.<br /><br />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 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 tires with this wedge did not adequately resist the initiation and propagation of belt-edge cracks between the steel belts. During March and April 1998, Firestone changed the material composition and increased the gauge of the wedge in its Wilderness AT tires (and some other tire models).<br /><br />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. <br /><br />Another relevant feature is the design of the shoulder pocket of the focus tires, which can cause 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.....<br /><br />Under the National Traffic and Motor Vehicle Safety Act, in order to compel a manufacturer to conduct a recall, NHTSA has the burden of proving that a safety-related defect exists in the manufacturer's products. The record of this investigation supports a determination that a safety-related defect exists in the focus tires manufactured by Firestone prior to its 1998 modifications to the belt wedge that are installed on SUVs. Although the agency has concerns about the possibility of future tread separations in focus tires manufactured after the wedge change, the available evidence at this time does not clearly demonstrate that a safety-related defect exists in those focus tires. NHTSA will, however, continue to closely monitor the performance of these tires.<br /><br />Therefore, on the basis of the information developed during the ODI investigation, NHTSA has 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.<br /><br />You can read the whole engineering report at:<br /><br />
http://www.nhtsa.dot.gov/hot/firestone/firestonesummary.html <br /><br />As soon as the media picked up on the problem I checked a friend's Mercury Mountaineer and found the treads about to fall off - The dealership rushed it in that very day after they took one look at them. The cracks were visible at a glance. And, I am talking about Boston not Arizona or Nevada....<br /><br />I for one would never buy a Firestone/Bridgestone tire after that. JMHO
