The Spitfire Formula Four Conical 97a skateboard wheels have a larger contact patch. Spitfire released their new Formula Four wheels a few years ago now. The latest formula was designed for higher abrasion resistance. This means it is a little harder to flat spot. Formula Four 97a wheels are generally decorated with a turquoise themed graphic. Unless of course it is one of the signature wheels. The signature wheels feature artwork custom designed for each rider. The 97a wheels are the softest Formula Four wheels made but they are still considered a hard wheel. The 97a formula will provide a little more grip on super smooth surfaces and is a little more forgiving to ride on rougher surfaces. There are no hard and fast rules, best to try out different wheels and select what works best for you.