Main gear shock cords (bungees) are made of natural rubber encased in woven cotton. The cotton casing provides some friction between wraps and adds to the shock absorbing capability. Inferior, non-aviation cord does not stretch properly and if used, may result in bent gear and fuselage tubing. After 1993, Avid changed the cords to accommodate the increased gross weight of the Mark IV. These cords are 90" long and require 7 wraps.