Many scooters are single gear but not all. A number of the bigger ones have a CVT type device that works like a centrifual clutch (or is one sometimes). The bike never "shifts" but it is constantly changing it's gear ratio so that it works like gears, just no shifting. Similar to how the new Prius works. It's actually a really good idea and is very efficient, but I LOVE shifting gears. Either in a car or on a bike, I like a manual trans.