Standard

SAE J1380

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Omfang

Basic Methods—The force, torque, and energy methods of measurement are all in common use and should yield the same test results. Effects of steering, traction, and non steady-state tire operations are excluded from the recommended practice because they are still in the research state. Methods of correcting laboratory data to road conditions are being developed. FORCE METHOD—The chief advantage of the force method is than the only parasitic losses in the measurement are tire the wheel assembly. The main disadvantage is that the small longitudinal spindle force, which includes the rolling resistance, may be seriously affected by the very large tire vertical load or by transducer crosstalk. The elimination or compensation of both effects is necessary. A secondary disadvantage is that the loaded radius of the tire must be measured in order to convert spindle force to rolling resistance. TORQUE METHOD—The torque method has the advantage that the measurement is direct and simple, as the rolling resistance is merely the torque reading divided by the laboratory test wheel radius. Equipment can be calibrated to read directly in rolling resistance if so desired. The main disadvantage of the torque method is that the parasitic losses contained in the measurement included test wheel losses as well as tire spindle rotational losses. The parasitic losses are larger than for the force method and can be of the same order of magnitude as the rolling resistance itself. Another disadvantage is that speed-hunting oscillations in the drive motor can introduce errors. ENERGY METHOD—The advantage of the energy method is the low cost and simplicity of instrumentation. No force or torque transducer is necessary. A voltmeter and an ammeter to measure the electrical energy input to the drive system are sufficient. The chief disadvantage of the energy method is that electrical losses are included in the measurement, in addition to all the other parasitic losses of the system. Thus, the parasitic losses are even larger than for the torque method. In some laboratory environments, special control may be needed to prevent line voltage fluctuations from creating power surges which can distort the readings.

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