Determination of Coastdown Mechanical Loss Ambient Correction Factors for use with J2263 Road Tests

Testing for vehicle emissions and fuel economy certification occurs primarily on chassis dynamometers in a laboratory setting and therefore the actual road conditions, such as forces due to tire rolling resistance and internal friction, must be simulated. Test track coastdown procedures measure vehicle road load forces and produce an equation which relates these forces to velocity. The recent inclusion of onboard anemometry has allowed the coastdown procedure to account for varying wind effects; however, the new anemometer based mechanical loss coefficients do not take into account ambient weather conditions.

The two purposes of this study are (1) to determine the new tire rolling resistance temperature correction coefficient that should be used when test ambient temperature is different from the standard reference value of 68°F, and (2) to investigate the effects of auxiliary measurements, such as other ambient conditions and vehicle settings, on this correction coefficient. In order to estimate the correction coefficient and to determine the effects of the other conditions a test procedure was executed on 12 vehicle/tire combinations for temperatures ranging from 40° to 100° Fahrenheit.

The recommended formula for adjusting the tire and mechanical drag for temperature is explicitly stated.