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Current SAE practices for evaluating potential improvements in fuel economy on heavy-duty vehicles rely on gravimetric measurements of fuel tanks. However, the recent evolution of portable emissions measurement systems (PEMS) offers an alternative means of evaluating real-world fuel economy that may be faster and more cost effective. This paper provides a direct comparison of these two methods based on a recent EPA study conducted at Southwest Research Institute. More than 228 on-road tests were performed on two pairs of class 8 tractor-trailers according to SAE test procedure J1321 in an assessment of various chassis components designed to reduce drag losses on the vehicle. During these tests, SEMTECH-D™ portable emissions measurement systems from Sensor's, Incorporated were operating in each of the vehicles to evaluate emissions and to provide a redundant measure of fuel economy.

Dynamic traction testing of a sample of drive tires for class 8 tractor-trailers provides information about the relation among rolling resistance, tire design, and traction performance in snow conditions. The tests were conducted to address concerns that low rolling resistance tires used to save fuel and reduce emissions may have inferior traction on snow. In addition to the dynamic traction testing, based on ASTM F-1805, rolling resistance was tested using ISO 28580, and characteristics of the tread design were measured, including tread depth and void ratio, using ASTM F421 and ASTM F-870. In general, tires designed for increased traction, usually made with open shoulders, had a higher snow traction rating than tires designed for highway applications with closed shoulders. There was no significant correlation between the snow traction rating and the coefficient of rolling resistance.

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.