Surly

Knard 650bx41 60tpi Folding Bead Tire

This is a similar Knard tread previously introduced on a 29 x 3? casing, made up of low, closely spaced knobs, an effective tread for going fast over varied terrain.

Surly chose 41mm because it's meaty enough to conform to the ground surface, absorb irregularities and provide a decent sized contact patch.