Adidas has been pushing the boundaries of what trail running shoes can look like and how they’re constructed, and the new Terrex X-King is no exception. Adidas adds the Terrex X-King to a line of innovative trail runners that also includes the Response, XT Boot, Supernova Riot, Agravic, and Raven. With Boost technology in the soles and seemingly few constraints on the construction of uppers, Adidas is a mile ahead of most trail shoe companies when it comes to innovation and design. The Terrex X-King carries on that tradition. The new model is comprised of two separate elements – an external shell and a removable midsole. The external shell has a Continental rubber outsole with massive square lugs wrapped around and heat-bonded to a high-density nylon upper. The inner element is a one-piece unit with combination rock plate, 6mm-drop EVA foam midsole, and insole. If the model is successful, presumably Adidas will offer different midsole inserts with different specs to purchase separately. Put them together, and the Terrex X-King is basically a mountain bike tire you can lace up and run in. Our wear-testers were impressed by the innovative design and aggressive grip, but ran into some issues with the way the removable midsoles fit and the overall sizing of the shoe. As one wear-tester put it, “I kept trying it over and over hoping to like it, but in the end, they just felt heavy, clunky and uncomfortable to run in.” 

Comfort
The majority of running shoes are constructed with a strobel, which is a method of stitching the upper (usually made of mesh with some type of overlays for structure) to the midsole (the foam foundation forms the shoe’s footbed. The Terrex X-King upends this traditional construction by making the midsole a fully removable, replaceable element. While the EVA foam midsole itself is comfortable enough, the lack of a strobel or firm connection to the uppers and outsole felt awkward to wear. Our wear-testers noticed the midsole edges underfoot and their insteps, toes and heels pressing the open gaps between the midsole element and the outer shell. The Terrex X-King is also only available in full sizes, so runners who wear half-sizes will need to go up or down to the next size. 

Speed
A burly, aggressive trail like the Terrex X-King pays a weight penalty for the protection it provides. This model comes in at 11oz for men’s size 9, which is one of the heaviest in this round of testing. Despite the heavy weight, the Terrex X-King ran smoothly with a relatively quick foot turnover. On challenging, technical terrain and in muddy conditions, wearers can run quickly with confidence thanks to the large lugs and Continental outsole’s sticky rubber compound.

Security of Fit
Our wear-testers found it exceptionally difficult to get a secure fit in the Terrex X-Kings. The model is only produced in full sizes, with no half-sizes available. Runners with larger feet are also out of luck, since 12 is the largest size available. Sizing is also confusing due to unclear conversions from international sizes. One wear-tester was provided with a pair of size 12 Terrex X-Kings, which were also marked 12UK, a size that’s equivalent to US13. Beyond sizing difficulty, the thin speedlaces were difficult to adjust and tended to come loose.

Agility
The Terrex X-King’s extra-deep lugs dig into soft ground and plow through wet and challenging terrain, while the sticky rubber grips smooth surfaces like large rocks and off-camber singletrack. Our wear-testers appreciated the excellent traction, but the separation between the outer shell and removable midsole reduced the trail feel considerably. One wear-tester reported that running the Terrex X-King felt a bit like running on a platform above the trail.

Responsiveness
The soft rubber lugs combined with thick, supportive EVA foam midsole produce a responsive ride. One advantage of the Terrex X-King’s innovative design is that Adidas could produce a line of aftermarket midsoles to swap in for different preferences, conditions, and uses. The stock insole is marked “Ultralight Raceflat 6mm,” and presumably, Adidas intends runners with Terrex X-Kings to have a stable of different midsoles to swap into the outer shell. This is another innovative, completely unique feature of the Terrex X-King that no other trail company has done anything like.

Protection
The rubber sole has deep lugs that run all the way to the medial and lateral edges of the outsole, but it also wraps around the mesh uppers approximately half and inch. The result is a seamlessly integrated protective element. The thick, dense nylon uppers prevent the intrusion of trail dust, although they are not waterproof. The removable midsole element also has a built-in rock plate, which further protects runners’ feet from sharp intrusions.