Rounded toe box allows full toe splay without being excessively roomy
Great midsole flexibility from heel to toe
Low stack height
6mm drop offsets some of the barefoot mechanics
Limited impact areas on outsole
The Nike Free Flyknit 4.0 is more flexible than Nike’s Free 5.0 and more cushioned than the Flyknit 3.0—it falls into the sweet spot where natural biomechanics intersect with high performance. The shoe feels like an extension of your foot, but provides just enough cushioning and responsiveness to comfortably roll through the miles.
Security (of fit) The uppers on Nike’s Free series have undergone a number of iterations, but the Flyknit 4.0 has the fit locked down. The upper has a slight amount of stretch to accommodate various foot shapes, but enough strength to hold its shape. The traditional lacing system distributes tension very evenly and effectively through the midfoot, and Flywire bands on either side of the laces hold the upper securely onto the midsole. Considering how minimalist its material construction is, it’s quite impressive that there was no slipping or movement inside the shoe during our testing.
Stability (on impact) A rounded toe box allows room for full toe splay and stability with midfoot landings. However, with extremely limited outsole reinforcement many runners will have impact areas that don’t align with the grippy rubber. That could compromise traction and cause excess wear. There’s no outsole rubber across the metatarsal heads, where many of this shoe’s demographic (midfoot strikers) would like it. The EVA material has minimal grip on its own, and is sketchy in wet conditions as well.
Smoothness (flexibility) The midsole EVA of the Nike Free Flyknit 4.0 strikes a nice balance of cushioning and responsiveness; it’s quite easy to roll from one step to the next. There’s a slight curvature to the midsole/outsole, slightly upward in the heel and toe box, which promotes midfoot landing – and it would work almost perfectly if not for the 6mm drop, which seems to counteract the sole curvature. The new flex groove hexagonal midsole consists of deep cuts along the length and width of the shoe, and provides outstanding flexibility as well as smooth transition from heel to toe.
Comfort The Nike Free Flyknit 4.0 upper feels like a comfortable sock, and is highly ventilated to cool efficiently and dry quickly. The last is anatomically true, and the rounded toe box on the Flyknit 4.0 is a significant improvement over the narrower 3.0, and prevents any chafing or constriction even with high mileage. The heel cup is thin but comfortable, and the entire interior surface feels soft against the skin. There’s minimal padding, but really no need for it because material construction of the uppers is so remarkably comfortable.
Speed and agility This shoe is built to fly—it’s lightweight, low profile, and comfortable, with a smooth ride and high responsiveness. Its limited traction is a drawback, but if you stick to roads or track ovals, there’s nothing to compromise your top end speed.