RC4Less foam tires. Our "R" series foam is Natural Rubber foam with a higher rubber content which is excellent for racing on low bite carpet tracks and outdoor asphalt and concrete surfaces. ("R" Series includes SOFT PINK, PINK, MAGENTA, PURPLE & RED)  Our “C” series foam is Exotic Rubber foam with a lower rubber content than the Natural Rubber foam. ("C" series includes WHITE, CREAM, TAN, GRAY, BLACK & HARD BLACK). Durometer ratings are indicated with each compound designation. Use the pull down menu to select your compound.