The Thunderbird is speed 9 driver with controllable, accurate flights. It has the stability of a TeeBird with the speed of a Valkyrie The DX line offers the widest selection of models and weights. These discs are affordably priced and provide an excellent grip in a variety of weather situations. DX discs wear in with usage and over time will eventually take on new and varied flight characteristics. Many top pros carry several DX discs of their favorite models to provide different flight patterns for different situations.