In December 2007, the United States Congress enacted the Energy Independence and Security Act (EISA) that mandated the USDOT-NHTSA to establish a national tire fuel efficiency rating system for motor vehicle replacement tires. The rolling resistance of each tire results in an energy loss for the vehicle and thus affects the vehicle’s overall fuel economy. However, improvements in one aspect of tire performance, such as rolling resistance, may lead to reductions in other performance aspects, such as traction and treadwear.

As part of the development of the tire fuel efficiency rating system, NHTSA initiated two phases of research. The Phase 1 research focused on identifying the best rolling resistance test method for use in a rating system, with results being published in a full agency report and summarized in a paper at ESV 2009 (09-0300). The Phase 2 research examined possible correlations between tire rolling resistance levels and vehicle fuel economy, wet and dry traction, outdoor and indoor treadwear, and tread rubber properties. The Phase 2 results were published in a full agency report and are summarized in this paper.

Overall, the Phase 2 results indicate statistically significant improvements in vehicle fuel economy when using low rolling resistance tires and proper inflation pressure, with no expected impact on tire dry traction or treadwear rate. However, the tire models tested exhibited a strong and significant relationship between better rolling resistance and poorer wet slide friction. The wet peak friction displayed the same tendency, but the relationship was much weaker. An analysis of tire tread rubber compounds indicated that the type of polymer, type of filler, and amount of filler can influence both rolling resistance and wet traction properties.