A scooter is a style of two-wheele motor vehicle traditionally defined by characteristics such as a step-through frame, wheels less than 16" in diameter, and an engine located below the rider and to the rear. Though throughout the history of scooters, there have been models which challenged or defied this definition, incorporating elements or designs from motorcycles (distinguished by a tank between the rider and handlebars and an engine located beneath the rider and to the front of the vehicle) and mopeds (which have pedals), developments over the past 20 years have broadened the "scooter" label to include a wide array of vehicles and designs featuring many different technologies and capabilities. Modern scooters cover a broad spectrum of designs: step-through or step-over frames, small or large wheels, front fairings or floor boards, and manual or automatic transmissions (found on most new scooter models).