GBC XC-Master ATV Bias Tire - 21/7-10 Remastered and Ready to Race. A redesigned profile makes the XC-Master the go-to cross country tire for excellent steering and control. Its X-knob tread pattern delivers superior handling while the puncture-resistant casing was formulated with the endurance necessary to handle cross country rides and races. Available in both front and rear tire designs. Sold individually.