Schwalbe Smart Sam 700 x 42c Performance Line Gravel / MTB TyreSchwalbe Smart Sam 700 x 42c Performance Line Gravel MTB Tyre The compact central rib provides comfortable rolling; the edged outer lugs guarantee optimized off roadgrip. This compound is created using completely new formulas. Schwalbe purchases advanced raw materials only with the worldwide best quality. Basically, Schwalbe has significantly increased the filler content for silica and now controls the mixing process more accurately than ever before.