Because of obvious complications it is too difficult to calculate the stresses in the cords of a tire. In this work the direct measurement of strains was undertaken. Two techniques will be discussed; (1) the measure of the increase in length of the cords in the outside ply, and (2) a radiographic technique in which the change in length of the cord elements, marked by steel wires, is followed by photographic methods. The measurements on a number of tires are presented. The cords in a tire are strained about 2% by the inflation pressure. When the tire is loaded some of the cords are thrown into compression and some into more tension. During the rotation of the tire the cords are thus subjected to a vigorous alternation of compression and tension (± 2%). At the same time the angles between the cords change by as much as two degrees. A few general applications are mentioned and their importance to the tire engineer is indicated.