Developed to Aim for Sub-4, ASICS's Latest Shoe, the "S4"

Named after the four S's: Speed, Stability, Safety, and Sub-4, the S4 is a model developed for runners aiming to complete a full marathon in under 4 hours, commonly referred to as Sub-4.

Incorporating the essence of the "METASPEED" series, the carbon-plated shoe boasts several features. So, what are the differences between this shoe and the "METASPEED" series or the similarly carbon-plated "MAGIC SPEED"?
 
Sub-4 is a challenging target that requires ample preparation time and rigorous training. In racing-oriented Japan, many runners are practicing diligently to aim for Sub-4, and the "S4" is squarely designed to support achieving this goal.

The development of the "S4" began at the request of ASICS President, CEO, and COO Yasuhito Hirota, who is an avid runner himself, asking the development team to "create a shoe for Sub-4." This fact vividly illustrates how dedicated the development was to the “Sub-4” concept.

Equipped with Features Necessary to Achieve Sub-4

To achieve Sub-4, runners must maintain an even pace from start to finish, running each kilometer in approximately 5 minutes and 40 seconds. This requires a considerable speed, which is supported by the carbon plates and the highly responsive foam material.
 
"The upper layer of the two-layered midsole features the lightweight, highly responsive FF BLAST TURBO, which is also used in the METASPEED series.

"Moreover, it incorporates a V-shaped carbon plate, similar to what’s found in the METASPEED EDGE+, adjusted for Sub-4 specifications. This helps ensure stable movements from landing to pushing off, supporting the runner’s forward motion till the latter stages of the race," says Yuhi Tanigaki, who was in charge of the development.
 
The rigidity of the carbon plate is adjusted so that even runners at the Sub-4 level, who may not have the muscle strength of elite runners, can benefit from the plate’s springiness.
 
Stability is a significant element for supporting a 4-hour run. Compared to the "METASPEED" series, the shoe's forefoot and heel of the sole have been made wider in the "S4," increasing the contact area and allowing for more stable footwork.

Additionally, by making the rubber thicker in the heel area than in the forefoot, the shoe's abrasion resistance upon landing is also increased. The FLYTEFOAM used in the lower layer of the midsole also contributes to improved stability.

"From observing test runs, it was confirmed that runners at the Sub-4 level often have worn-out heels, suggesting they tend to land on their heels in the latter stages. Therefore, we devised a structure that ensures stability and smooth forward transition even when landing on the heel. We believe you will find it easier to move your foot forward even after 30km when fatigue sets in."
 
The upper is made of the lightweight, breathable Motion Wrap Upper used in the "METASPEED" series. The shoelaces also feature the same concave-convex design as the "METASPEED" series, making them less likely to loosen during runs. Every detail is finely tuned for racing.