Quantitative Estimate of the Relation Between Rolling Resistance on Fuel Consumption of Class 8 Tractor Trailers Using Both New and Retreaded Tires

Road tests of class 8 tractor trailers were conducted by the US Environmental Protection Agency (EPA) on a new and retreaded tires of varying rolling resistance in order to provide estimates of the quantitative relation between rolling resistance and fuel consumption. Reductions in fuel consumption were measured using the SAE J1231 (reaffirmation of 1986) test method. Vehicle rolling resistance was calculated as a load-weighted average of the rolling resistance (as measured by ISO28580) of the tires in each axle position. Both new and retreaded tires were tested in different combinations to obtain a range of vehicle coefficient of rolling resistance from a baseline of 7.7 kg/ton to 5.3 kg/ton. Reductions in fuel consumption displayed a strong linear relationship with coefficient of rolling resistance, with a maximum reduction of fuel consumption of 10 percent relative to the baseline. The return factor for the new tires was 1: 3.1, that is, a one percent decrease in fuel consumption is obtained by a 3.1 percent decrease in rolling resistance. These results are consistent with earlier studies conducted in the 1980s despite the numerous changes in truck design made since that time. Equipping a tractor with low rolling resistance tires provided 7.4 percent of the reduction of fuel consumption, even when baseline tires were used on the trailer. Retreaded tires provided a lower reduction in fuel consumption, with a return factor of 1:4. Retesting of both new and retreaded tires provided reductions in fuel consumption of 7.3 to 7.6 percent suggesting that the first test result may have been an anomaly. The results demonstrate the value of conducting multiple SAE J1321 tests to evaluate variability in on-road testing.

The relationships derived from the tests approximate what would be expected based on mathematical models. These results can be used to estimate reductions in fuel consumption and emissions from tires without additional road testing, and they can be used to characterize potential benefits using vehicle models of fuel consumption and emissions.