Two bicycle tires are set rolling with the same initial speed of 4.00 m/s along a long, straight road, and the distance each travels before its speed is reduced by half is measured. One tire is inflated to a pressure of 40 {rm psi} and goes a distance of 17.8 m; the other is at 105 {rm psi} and goes a distance of 93.5 m. Assume that the net horizontal force is due to rolling friction only and take the free-fall acceleration to be g = 9.80 m/s^2. What is the coefficient of rolling friction mu_r for the tire under low pressure?