TIRE FAILURE ANALYSIS - BEAD FAILURE


by
Charles C. Roberts, Jr

.

Figure 1 is a typical cross-section of a pneumatic tire. The bead is the inner edge of the tire that contacts the wheel flange and presses against the bead seat. The bead seals against air loss in tubeless tires and grips the wheel rim for transmitting various loads such as steering, traction and braking. Bead failure can cause loss of air


FIGURE 1


FIGURE 2



pressure in the tire as well as detachment of the tire from the rim. Bead failure may cause loss of vehicle control and, possibly, an accident. Figure 2 is a view of a new tire that sustained a bead failure after approximately 100 miles of operation. The failure resulted in tire deflation. The bulge in the tire, caused by the bead failure, was on the inside of the tire and could not be easily observed. Figures 3 through 5 show various closer views of the bead failure. Apparently, the reinforcing plies surrounding the bead wire failed, causing loss of support and separation from the bead.


FIGURE 3


FIGURE 4


FIGURE 5



The air pressure in the tire caused a bulge and eventual deflation of the tire. The tire remained on the rim and, when removed from the vehicle, no evidence of a problem could be found. After the tire was re-inflated, the bulge caused by the bead failure was apparent. In this example, the failure is a result of a tire deficiency in manufacture. Not all bead failures are the result of a defect in the tire. Other possibilities are impact with a non-compliant object, over-pressurization of a tire, and improper installation. Figure 6 is a view of a tire that suffered a bead failure, most likely, because of


FIGURE 6



an impact with a curb. The deformation to the rim tends to substantiate the conclusion. When tire disablement is a possible cause of an accident, investigation as to the probable cause is warranted. Bead failure is one of many disablement causes. See Insurance Adjuster Magazine, July 1986, as well as the "Technical Notebook", for additional information on tire failure analysis.


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