Inconsistencies in Setting Chassis Dynamometer Dissipative Loads with Particular Reference to the LA4 Cycle

Two previous interlaboratory correlation studies using a specially instrumented car on a series of twin roller dynamometer installations are reviewed. The current practice of setting a fixed tyre inflation pressure in such correlation studies means that effective rolling circumference of the test vehicle's tyres may be poorly defined and arbitrary. In addition, inconsistencies in the basis for measuring speed, when transferring from road to dynamometer and between dynamometers with twin rollers of different diameters, may lead to a systematic bias error in the speed of the twin rollers. The effect on fuel consumption and exhaust emissions are evaluated under hot start conditions over the speed-time profile of the Australian Standard AS2077 City Cycle, identical to the LA4 cycle.