The biggest differentiation in the nike free run 2 is its outsole. Instead of a layer of rubber covering the outsole surface, Nike Free uses a hard wearing foam unit with outrageously generous siping or grooves across the length and breadth of the surface, prioritizing flexibility and natural gait management over everything else. Small pieces of rubber are overlaid in the heel and toe-off area, adding an element of zonal durability. The shoes from the Free pack are further segmented on a scale of 1-10, 1 being running barefoot and 10 being a conventional http://www.salefreerun.com/nike-air-max-2011-c-11.html nike air max 2011 running shoe with all the bells and whistles. In 2005, when Nike released the original Free, they were unsure of how people would react to this radically new concept, so the first Free was a 5.0, a shoe which sat midway between running barefoot and a traditional running shoe. Over the years, Nike added the Nike free 3.0, nike free 4.0 and the nike free 7.0. This summer though, Nike focuses only on the nike free run 3 2012 summer. While the reasons are unclear for doing that, we’d have preferred a 3.0, 5.0 and the 7.0 since that allows for better segmentation.