The Formula Four Conical Full skateboard wheels feature Spitfire's performance urethane that lasts longer and withstands more abuse than the competition. Pick which duro you're looking for after assessing the varying attributes, 'cause this is getting technical.
Spitfire Duro 101–The Duro 101 by Spitfire is harder of the two durometers, they will be faster in a skatepark than the 99Duro wheels, but are also more slippery. They will last longer because of a harder Durometer but not be as smooth in the streets as a 99D.
Formula Four Urethane–Unmatched abrasion resistance (no flat spots), more controllable grip, lasting speed everywhere, smooth anti-stick slide, longer lasting (holds size and shape longer).
Conical Full Shape – With a wide riding surface and a cutaway design, this shape has unmatched control and lasting speed everywhere.