Skatepark Formula™ (SPF) is very high quality urethane specifically formulated to resist flatspotting on slick or smooth surfaces while maintaining a higher rebound for a quicker response and a faster roll. Skatepark Formula™ has a high resistance to abrasion while not compromising hardness and slide ability. Simply put… Skatepark Formula wheels grip better on slick surfaces, are almost impossible to flatspot, and are the fastest, longest lasting wheel on the market today. You won’t find BONES’ Skatepark Formula from any other wheel supplier so get a set and find out for yourself what the word on SPF is all about. Specifications: Wheel Core: No Wheel Diameter: 58mm Wheel Width: 33mm Wheel Hardness: 84B (equivalent to 104A) Wheel Formula: SPF Wheel Color: Red Wheel Suggested Use: Skateparks Wheel Surface: Smooth