this report examines the factors affecting the fuel consumption of heavy commercial vehicles. from the experience gained in these preliminary tests it is apparent that some accepted driving cycle is required on which to base any comparative measurements. dynamometer tests on multi-axle vehicles require extensive test facilities, therefore selected test routes covering a range of operating conditions would appear to be a requirement. the largest part of the power loss is in the engine and alternative methods of propulsion are being considered throughout the world. however it would appear that any improvement in the immediate future will be in further developing the diesel powered vehicle. tyres account for a predominant part of the remaining power consumption, in rolling resistance, cornering and slewing forces. these forces also contribute to the tyre wear and will be affected by the type of tyre and the tyre inflation pressure. vehicle warm-up is essential when making any comparisons of fuel consumption and this includes the combined effect of the engine, transmission and tyres. aerodynamic shaping can materially improve the fuel consumption if the vehicle speeds are high enough. the problem of comparative testing where wind strengths are above certain mean levels must be carefully considered in relation to the test programme objectives.(a)

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