Bones X-Formula Hawk Beak & Destroy V5 Sidecut 99A Wheels 58mmX Formula (XF) is another industry leading innovation from the BONES WHEELS factory. X Formula rolls over rough terrain like softer wheels do, but slides more like a harder wheel would. Speed: X Formula is extremely fast because it has a super high rebound. They roll much smoother and faster on all terrains because it absorbs vibration and softens impacts much better. Grip & Slide: The slide ability comes from its unique blend of high performance