Strain gage instrumented transducers were used to measure the cord loads at a number of locations in several different automotive tires loaded against both flat and cylindrical road wheel surfaces. The two basic types of cord load fluctuation encountered in all automobile tires have been identified from these measurements, and the most severe location for cord load fluctuations has been closely bracketed. By these measurements, it has been possible to show that for each tire definite relations exist between the cord loads induced while running on a cylindrical drum and while running on a flat surface. The maximum cord load fluctuations in a tire are the same for the NBS roadwheel and flat surface when the tire is loaded against the roadwheel with a load of between 85 and 90% of that used on the flat surface. This result, while obtained on the basis of a very limited number of tire tests, agrees well with the figure of 88% which has been reportedly used in some industrial testing programs.There exists no combination of load and pressure for which it can be reliably stated that tire cord loads while running on the cylindrical roadwheel are the same throughout the tire as when running on a flat surface.