Sram: THE BEST of both worldsSRAM DD3 is a unique shifting system that combines a three-speed gear hub with a traditional cassette body controlled by a derailleur. It gives you all the gearing you need, but simplifies the system by putting all the controls in one hand. This means a bike thats easier to use, and lets you focus on what you love most: riding.The gear hub can be shifted at any time, even under load or standing still. The cassette provides a wide range of gears for maximum versatility. Its built for the rider who needs lots of gearing options for touring or hilly terrain.