The Mainline is S&M's trail tire which comes in wire bead only with a mid weight, high pressure casing. The 2.1 has a micro knurled surface on a directional tread designed to go on the rear. It features a center tread with a V-notched edge for accelerating and a flat edge for braking. The 2.425 front tire size is a nod to the old 2.125 Comp III we grew up riding in the front. Additional angular raised sections on three rows of knobs help keep the larger Mainline in front!