Gas mopeds are essentially motorcycles with small-displacement engines that offer highly economical transportation. The motor-vehicle laws governing them vary considerably in various jurisdictions around the world. These differences result in some confusion about exactly what a moped is, and, in some cases, influence engine size, design factors, and even the name used to describe the vehicle. Gas mopeds typically have engines that range in size from ultra-small, two-cycle designs to 250-cc, four-cycle engines. While there are some three- and four-wheeled models, most mopeds have two wheels and either a step-through design like a motor scooter, or a step-over frame like a conventional motorcycle.
While motorcycles and bicycles equipped with small-displacement engines have been manufactured since the early 20th century, the term "moped" only came into use in the 1950s and generally referred to several brands of small motorcycles or motor scooters with step-through frames, engines of about 50-cc or less, and auxiliary pedals. As engines, clutches, and transmissions have grown more efficient, most gas mopeds today no longer have pedals.
In many jurisdictions around the world, the legal minimum age for moped drivers is lower than that for conventional motorcycles or automobiles. A number of countries limit the engine displacement of gas mopeds to less than 50-cc, and, as a result, some models are equipped with 49-cc engines. In U.S. states and many countries, mopeds may not be driven on high-speed roadways and may be subjected to specific maximum and minimum speed laws. In considering the use of a moped, potential buyers should familiarize themselves with the local laws that govern gas mopeds.
Historically, the smallest gas mopeds were little more than bicycles equipped with very small gasoline-powered engines that provided power as an adjunct to the pedaling done by the rider. This auxiliary pedaling was often essential on hills. Today, even the smallest gas mopeds typically have enough power to handle most inclines. In the U.S., beginning in the 1990s, a number of smaller manufacturers began producing limited-run mopeds equipped with high-performance engines and racing-like cosmetics. While still meeting the less stringent licensing requirements of other mopeds, they helped create a small yet devoted audience of enthusiasts who bought these high-performance models.
Along with high-performance gas mopeds, the market has seen the introduction of other specialty moped designs. These include three- and four-wheel models, some intended as small-scale taxis and utility vehicles. With ready access to inexpensive used mopeds in most developed countries, moped racing has become popular as a low-cost motor sport.