Marathon Industries 01014 9x3.50-4-Inch Flat Free Tire with Smooth Tread- 4 , New, Free Shipping This smooth tread, flat free tire is designed for the front caster on zero turn mowers and other equipment. Marathon Flat Free tires provide the bounce and load handling characteristics similar to an air-filled tire with the benefit of never going flat. Product Features and Specifications 9x3.50-4 Tire. 9.3 Tire Diameter. 3.3 Tire Width.Flat Free Tire made of solid, polyurethane foam. Non-marking.