Article of footwear with upper and sole structure having substantially equal coefficients of friction

An article of footwear comprising:

• an upper including a one-piece, unitary outer unit that has a forefoot region, a midfoot region, and a heel region;
• wherein the outer unit is comprised of rubber and has a side portion with an exterior surface that has a first coefficient of friction;
• a sole structure secured to the upper;
• wherein the sole structure is comprised of polymeric foam and has an exterior surface that has a second coefficient of friction and that underlies the exterior surface of the side portion of the outer unit;
• wherein the first coefficient of friction is substantially equal to the second coefficient of friction;
• wherein the forefoot region of the outer unit has a toe box region and a vamp region, the toe box region is adjacent to the sole structure and between the sole structure and the vamp region, the toe box region has a first thickness, and the vamp region has a second thickness less than the first thickness;
• and
• wherein a boundary between the vamp region and the toe box region extends around the forefoot region of the outer unit from a medial side of the outer unit to a lateral side of the outer unit and extends rearward to an ankle opening defined by the upper.

An article of footwear comprising:

• an upper;
• a sole structure secured to and underlying the upper;
• wherein the upper includes a vamp region having a boundary extending around a forefoot region of the upper and extending rearward to an ankle opening in the upper;
• wherein a thickness of the upper changes from a first thickness to a second thickness of the vamp region at the boundary, the second thickness less than the first thickness;
• wherein the upper has a first material composition at an exterior surface of the upper, and the exterior surface of the upper with the first material composition has a first coefficient of friction;
• and
• wherein the sole structure has a second material composition different than the first material composition at an exterior surface of the sole structure directly underlying the exterior surface of the upper that has the first coefficient of friction, the exterior surface of the sole structure having a second coefficient of friction, and the first coefficient of friction is substantially equal to the second coefficient of friction.