Battery Electric Buses (BEBs) place severe mechanical stress on tires. A long-term study of BEB fleets by the National Renewable Energy Laboratory (NREL) has shown a 45% reduction that the average BEB tire life. Excessive tire wear has been reported to contribute over 140% increase in tire costs in BEB maintenance budgets. Further, tire maintenance costs have been estimated to be almost 143% higher than for compressed natural gas (CNG) bus fleets.
This project proposes a new material modification and processing in the manufacture of BEB tires. The method involves preparation of siloxane oligomers, adding a compatibilizer to avoid premature coagulation and phase separation, mixing the compatibilized siloxane oligomer to the natural rubber (NR) latex, followed by controlled shear blending and drying. The process creates a reinforced network of silica and NR within the tire tread and is essentially a drop-in technology to the current tire tread material manufacturing process. By controlling silica dispersion, the process breaks the tradeoffs between high tire wear and low rolling resistance, allowing for performance gains not attainable with current methods and materials.
The work plan will involve preparing a new tire formulation of NR and compatibilized siloxane to make prototype tires. The prepared material will be characterized using standard test methods for rubber materials. Prototype tires will be manufactured, and their performance compared with EPA SmartWay low rolling resistance tires and the tires of the collaborating transit partners. A fleet test plan and data collection strategy will be developed in collaboration with the transit partners. A transit impact analysis will also be conducted to evaluate the impact and adoption strategy. The material and tire manufacturing process will be scaled beyond laboratory to the pilot production stage along with the compound manufacturing process. Two transit agencies have agreed to run the tests on their fleets.
Benefits to the transit agencies of this new BEB tire technology will include lower maintenance costs, increased vehicle range and energy efficiency, increased use of low rolling resistance tires, less frequent tire replacements, and reduced labor for tire maintenance. Taking into account their longer life, these tires are also estimated to reduces the total BEB tire costs by 44%.
