The six main types of motorcycles are generally recognized as standard, cruiser, touring, sports, off-road, and dual-purpose. Sport touring is sometimes recognized as a seventh category or integrated with the touring category. Although there are many names and systems for classifying types of motorcycles based on their characteristics and usage, there are generally six categories recognized by most motorcycle manufacturers and organizations. Strong distinctions are usually made between the six main types of motorcycles and other motorcycles. Scooter, moped, underbone, miniature, pocket, electric, and three-wheeled motorcycles are generally excluded from the main categories but other classification schemes may include these as types of motorcycles. There is no universal system for classifying all types of motorcycles. There are strict classification systems enforced by competitive motorcycle sport sanctioning bodies, or legal definitions of a motorcycle established by certain legal jurisdictions for motorcycle registration, emissions, road traffic safety rules or motorcyclist licensing. There are also informal classifications or nicknames used by manufacturers, riders, and the motorcycling media. Some experts do not recognize sub-types, like naked bike, that "purport to be classified" outside the six usual classes, because they fit within one of the main types and are recognizable only by cosmetic changes. Street motorcycles are motorcycles designed for being ridden on paved roads. They have smooth tires with tread patterns and engines generally in the and over range. Typically, street motorcycles are capable of speeds up to , and many of speeds in excess of . Street motorcycles powered by electric motors are becoming more common, with firms like Harley-Davidson entering the market. Standard Standard motorcycles (also called naked bikes, roadsters, or simply standards) are motorcycles mainly intended for use on streets for commuting. They are characterized primarily by their upright riding position (in-between the reclining rider posture of the cruisers and the forward leaning of sport bikes) and most of the usable torque (powerband) at lower engine rpm for commuting and fuel efficiency. Standards are typically not equipped with fairings or windscreens from the manufacturer, hence the name naked bikes. Standard is often a synonym for naked, a term that was originally used in reference to 1950s road racing bikes. Footpegs are below the rider and handlebars are high enough to not force the rider to reach too far forward, placing the shoulders above the hips in a natural position. Due to their flexibility, lower costs, moderate engine output, and up-right seating