These inserts were designed to decrease the lateral deflection of the tire while at the same time increasing vertical impact absorption, to provide better handling in the bumps. Using a soft foam or hollowing out the inner circumference leaves the car feeling squirmy with a less accurate feeling through the bumps, not to mention a loss of durability. Gil Losi and Mark Pavidis knew this compromise was not the solution. The solution they found was the addition of lateral grooves to the inner diameter. The lateral grooves allow the insert to flex vertically, absorbing large impacts while still maintaining the lateral stability and overall durability AKA inserts are known for, providing you with a no compromise, high performance foam insert. The result is a more predictable handling car, with no sacrifice in insert durability.