They didn’t reinvent the wheel. They just built a better bike. The chainless two-wheeler by Dynamic Bicycles will leave your old ride in the dust. Instead of greasy chains and dirty derailleurs, Dynamic’s new design has an internal shaft drive, so there’s nothing to soil your hands or tear your pants to shreds. Shifting gears is simple — you can change anytime, not just when you pedal — and, thanks to the gear indicator, you always know what gear you’re in. Plus, Dynamic’s designs are high on style and, because all the key parts are protected, low on maintenance. Models include an eight-speed mountain bike, a seven-speed road bike, and a casual three-speed comfort bike. $550 to $800.