1992-11-01

City Bus Tire Bead Heat Evaluation 922457

Radial tires now approach 80% of the North American commercial tire business due to superior treadwear and fuel economy. One of the last areas for radial tire market penetration is the city bus market.A radial tire is less tolerant of high brake heat temperatures because: 1.There is less rubber and reinforcement bulk than a bias tire to act as an insulator in the bead area. 2.The steel ply is a good heat conductor. 3.High sulfur compounds are required for good wire adhesion and these compounds are susceptible to heat degradation. Radial tires are developed to withstand a maximum continuous running temperature of 90 degrees C. Exceeding this temperature for short periods causes no problem; however, longer exposure may cause a loss of material component strength. Therefore, it is important to know the heat flow characteristics between a brake drum and the tire.In this paper, various drum-bead heat studies will be discussed. From four city bus studies, the heat flow rate between a 16.5-inch brake drum and a 22.5-inch wheel will be presented. Other studies compare a 22.5-inch and a 24.5-inch wheel on the same brake drum, steel versus aluminum wheels, and wheel and drum cool-down rates.

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