Widely-spaced side knobs offer confidence on loose terrain while a smooth center tread minimizes rolling resistance Widely-spaced side knobs offer confidence on loose terrain while a smooth center tread minimizes rolling resistance S4 - Silica4, Formulated to maximize rolling efficiency while providing class leading grip in wet conditions ULT - Lighweight casing fabric utilizing smaller thread fabric, this casing uses less rubber-making the tire more supple and faster rolling, with improved traction