Challenge Gravel Grinder 650B x 46 - Tubeless Ready Gravel TyreChallenge Gravel Grinder 650B x 46 Tubeless Ready Gravel Tyre The Challenge Gravel Grinder is built to monster the toughest gravel events on the planet. With a fast rolling but grippy tread and tubeless ready construction, the Gravel Grinder is perfect for all round gravel use. Built around a fast rolling semi slick centre tread design, the Gravel Grinder rolls well on hard surfaces yet has enough purchase when braking or climbing to retain traction.