The AKA 1:8 Buggy and SC Grooved and Shaped Soft foam Insert is designed to improve handling on tracks with sharp edges and large jump falls. Helps absorb impacts from large vertical bumps but keeps the tires sidewall and profile shape even under hard cornering This gives you more constant handling performance in bumpy and rough sections on any track.
In more detail:
Gil Losi Jr and Mark Pavidis didnt want to use a softer material or hollow out the inner circumference of the insert so they have incorporated lateral grooves to the internal diameter of AKA's closed cell inserts. The lateral grooves allow the insert to flex vertically to absorb the large impacts while still maintaining lateral stability and overall durability AKA inserts are known for. The result is a more predictable handling car in the harshest track conditions. A stiff wheel combined with a laterally stable, vertically compliant insert equals faster lap times as Cody King proved when he used these inserts along with the new Evo wheel to take home the win at the 2010 IFMAR world championships.