A computerized system to automatically measure tire footprint areas has been constructed and used to study the variations in the tire footprint area characteristics as a function of various tire parameters. The individual system components including the optical vidicon, TV monitor, TV control and digitizer, computer, data storage device, printer and plotter are described and their function in the system explained. A flow-chart of the systems computer program shows the methods used to control the test, to collect and store the digitized visual data, to calculate tire footprint length, width, total footprint area, contact area and void area and to report the results. A description of the procedure used to calibrate the system and the various test procedures used to directly or indirectly measure the tire footprint areas are given. Comparisons including test time, test accuracy and test repeatability are made between this system and the traditional methods of measuring tire footprint areas.
The results presented in this paper include variations in footprint areas for a radial tire as a function of inflation pressure, tire load, and tire rotation. An explanation of the tire parameters which cause these variations are given.