Inflation pressure retention (IPR as a loss rate) is a key predictive parameter to improving tire durability. ImprovedTire IPR, manifested as reduced percent pressure loss per month values, has statistically been shown to be a direct resultof innerliner compounds made with increasing amounts of halobutyl rubber when used as a direct replacement for natu-ral rubber if other variables are constant. Roadwheel performance of tires is highest when using 100-phr of halobutyl rub-ber in the innerliner compound. This affords a tire with desirably low IPR loss rate values, desirably low tire intracarcasspressure (ICP) values, and increased tire durability as measured in hours until failure on laboratory roadwheels. The use of nitrogen gas in tires in severe service conditions is known, and a variety of benefits have been claimedfor use in passenger car tires. In order to test specific claims, tires with innerliners having a 100-phr bromobutyl rubber,and 80/20 and 60/40 bromobutylatural rubber blends were studied using three filling gases: dry, pure nitrogen (99.4%),dry air and a 50/50 mixture of dry nitrogen/oxygen (49.8%). Performance was measured for new and oven-aged tires. Itis shown that the direct benefits of using nitrogen are in reducing the Tire IPR loss rate values, and in reducing agingsince oxygen gas has been initially excluded. Other claimed benefits are found to be a secondary result of the lower TireIPR loss rate values. Use of nitrogen as the inflation gas does not benefit the measured cavity gas temperature or tirerolling resistance, both of which are shown to be tire pressure dependent, but not dependent upon the filling gas whenmeasured at equal tire inflation pressures.
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