STI Tech-4 XC Tire (21x7-10) STI Tire & Wheel now offers a smart choice to cross-country sport quad riders and racers with the release of the all-new Tech 4 XC. The STI Tech 4 XC brings high performance to the market at a surprisingly affordable price. The Tech 4 XC is specifically designed for serious trail riding and racing. It provides an extra level of trail durability with a 6-ply rating and utilizes a high-tech rubber compound that delivers exceptional hook-up on hardpack surfaces, in a unique tread pattern that pulls strongly through soft loam - a winning combination. Lightweight construction reduces unsprung weight and rotational mass for unmatched acceleration and ride.