Sidi dragon 4 c srs vernice mtb spd shoesthe heart of the revolutionary and patented mtb srs carbon sole is a pure carbon insert reaching from the heel to the toe the carbon insert as well as the replaceable dragon srs tread are bolted to a narrow durable nylon frame this unique design provides a slight amount of flex in the toe while retaining excellent stiffness and power transfer in the body of the shoe the sole is engineered for the high performance high mileage cyclist who requires a so