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Show ' tests show why tires wt last Eureau of Standards Uses Machines to Determine Facts on Rubber. Th. following conclusions have been hod ns to fnctors which inlluonee T life of tlrt'3' ncconlins l" P'Ur n hhiis just been Issued by the bu- standards. Department of CrTcn-ss ia which the fric-,, fric-,, rubber Is slightly compounded Lars to stand up better under test n one in which "pure gum is used, o Within the customary limits of .ir oressure used in tires, the higher "pressure the better the tire will stand UP- . , ,. . 3, Fabric tires develop a much Mher temperature than cord tires, niul lieir life is much less than cord tires. Separation Causes Failure. 4, Separation, which was the principal prin-cipal cause of failure in these tests, did not always take place in the same location in the tire. It occurred In most cases between the tread and breaker, breaker and cushion, cushion and carcass, or betweeif the outer two plies. 5. Any particular brand of tire usually sliowed a characteristic type of failure. 6. Some makes of tires "blow out" modi sooner after separation has started than otheis. ". Compounded inner tubes fur truck tires appear to withstand the action of heat better than those of the pure-gum type. Some Improvement Noted. It is interesting to note that of the tires tested, in general not more than one-half the samples passed the test requirements, although a general improvement im-provement was noted during the period pe-riod covered by the tests in the case of some tires. The publication briefly describes the testing machines developed by the bu reau for this work. By using these machines it is possible to determine in 48 hours facts which would otherwise other-wise require several months' use on the road. A table gives the results of the tests. This paper is-known as Technologic Paper ."o. 31S, and may be obtained from the superintendent of documents, government printing office, Washington, Washing-ton, D. C, at 10 cents per copy. |