Tested by Spitfire Team riders, Formula Four Performance Urethane lasted longer, withstood more abuse and performed superior to all other wheels. Spitfire Formula Four Urethane was developed to combine all the desired properties of a performance wheel without sacrificing any one attribute at the expense of another. Formula Four's True lasting Performance Urethane comes not from a single benefit, but from a combination of qualities and features that together produce a truly great wheel Formula Four Performance Urethane is unlike any other. Spitfire claim this is the #1 shape in skateboarding world wide. And it probably is. This shape first emerged in the early 90’s and has been a popular go-to ever since. It features a large radius from the bearing seat which produces a fairly narrow contact patch. It is the great all rounder.