J2263_199610 Road Load Measurement Using Onboard Anemometry and Coastdown Techniques

This SAE Recommended Practice establishes a procedure for determination of vehicle road load force for speeds between 115 and 15 km/h (71.5 and 9.3 mi/h). It employs the coastdown method and applies to vehicles designed for onroad operation. The final result is a model of road load force (as a function of speed) during operation on a dry, level road under reference conditions of 20 °C (68 °F), 98.21 kPa (29.00 in-Hg), no wind, no precipitation, and the transmission in neutral.

This document supplements SAE J1263 FEB96. SAE J1263 remains an alternative method for evaluating vehicle road load force during low wind conditions. This procedure incorporates recent advances in test equipment and data analysis; it defines vehicle road load force over an extended speed interval. Major changes are inclusion of real time anemometry to measure and compensate for wind conditions directly in front of the vehicle and use of a three term equation to model road force over a 115 to 15 km/h (71.5 to 9.3 mi/h) speed range. (The previous procedure relied on average wind conditions measured at distances up to several kilometers from the vehicle. Also, road load force was modeled by a two term equation and was, typically, simulated on a hydrokinetic dynamometer capable of being adjusted to reproduce this force at only one speed; performance at other speeds was a function of dynamometer characteristics.) In addition, this procedure specifically discusses and authorizes "split" coastdown runs which must be used when the test track is too short to allow a complete coastdown run due to the vehicle's performance, weight, or road load force characteristics.