A mobile test station has demonstrated its effectiveness in measuring straight-ahead traction coefficients of truck tires. This system - incorporated into a modified trailer-tractor combination - is designed to test the entire range of light-truck and heavy-truck tires now in production. The tire carriage assembly is installed in the center of the flat-bed trailer. The tire is hydraulically loaded to the ground through an opening in the bed. To ensure reasonably valid tire-traction data, the system is designed to minimize variations in such test parameters as load, brake line pressure, vehicle speed, and tire orientation. The mobility of the system makes it possible to test tires on various types of road surfaces, thus providing a complete spectrum of surface coefficients for both wet and dry conditions.