Around 55.5MM. Used for about 2 months. Hardness is 99, which is a basic hardness. Thick wheels and colored wheels are trending, so please give them a try! The shape is OG CLASSIC! See below for more details! 【FORMULA FOUR】 (F4) The newly developed FOURMULA FOUR wheels are designed to be faster, smoother, grippier, and more resistant to punctures. They have the performance to withstand long-term test rides by professional riders, and are considered to be the highest-performing wheels currently available. 【OG CLASSIC shape】 A wide CONICAL type shape reminiscent of the design when SPITFIRE was founded. This model has a wide contact surface, providing stability and high grip. It's slightly narrower than the popular CONICAL FULL, but has a wider contact surface. 【99DURO / 101DURO】 DURO is the hardness rating for Spitfire wheels. The F4 series is released in two types: 99DURO and 101DURO. 99DURO: Less affected by the road surface, suitable for all-around use from street to park. High grip but also easy to slide. 101DURO: Recommended for those who want speed on clean concrete parks, or those looking for wheels that are easier to slide.