Challenge Tire Gravel Grinder Pro H-TLR Tire 700 x 40 TanChallenge Gravel Grinder Pro Tire 700 x 40 Tubeless Folding Black Tan Handmade. Intended for all around or dirt gravel roads this tire comes equipped with a file tread center and a knobbier shoulder tread. File tread center pattern offers low rolling resistance on smoother terrain and increased grip when the road gets rough Shoulder tread is more aggressive for corner confidence and additional control The Gravel Grinder is ideal for hardpack gravel