"R" designates radial tire.
Nearly all tires today are radial. Therefore, if our tire chains charts show with or without the "R"; the snow chains will fit either designation. For example P195/75R-15 is the same as P195/75-15 or 11-22.5 is the same as 11R22.5.
Snow tires, Mud and Snow (M&S), recaps, deep lug mud tires and other oversized may require longer tire chains.