Mini-Logo Skateboards S4 101A Wheels Width: 28mm Formula: "ML" Hardness: 101A, we have been able to keep the Mini-Logo formula continuously ahead of all other MDI based wheels in rebound and abrasion. This provides skaters with the very highest in performance at a price point that makes them a real value. Mini-Logo Formula is an evolution of the white, MDI urethane we pioneered in 1977. This family of urethanes has grown to become an industry standard, and because we develop our own formulas in-house All Mini-Logo products come with a warranty