A hub motor is an electric motor that turns a wheel without the use of a transmission. This is accomplished because a hub motor is built directly into the wheel's hub, which is the point around which the wheel rotates. Because this bypasses the need for a transmission, hub motors are more efficient, especially at high rates of speed. It is common to find a hub motor on an electric bicycle.

Hub motors, as an idea, have been around for more than a century. They were originally conceived for use with automobiles, but today are used almost exclusively on electric bicycles. Motorized bicycles are a common sight in Asia, much more so than in the U.S., but technological advances are making them more popular in general. Some motorized bicycles are manufactured that way, but it can sometimes be cheaper to install a hub motor on a bike as an aftermarket add-on. There are many conversion kits available, including kits for modifying a Chinese hub motor to fit a bicycle of American dimensions.

Motorized bicycles equipped with a hub motor will most often also have functioning pedals. This is the case for two reasons. First, if the battery that runs the hub motor discharges, the bike will still need propulsion. Legal regulations may also prohibit the use of motorized vehicles which are not registered in the same way as motorcycles.

Hub motors run on electricity from rechargeable batteries. On a bicycle, the battery pack is usually located near the rear wheel. Lithium ion and nickel metal hydride batteries are the most preferred types of rechargeable battery because of their light weight. A lighter-weight battery can help to increase its range, which is the key consideration when using a battery-powered hub motor. Depending on factors such as terrain, rider weight, and weather, an electric bicycle can have a range as short as 4.3 miles (seven km) or as long as 43.5 miles (70 km).

When converting a pedaled bicycle to electric, the hub motor is usually installed on the front wheel. The motor produces high levels of torque on this part of the bike, and it is important to make sure the frame of the bike can stand up to these increased forces. Many bicycle forks -- the parts which mount onto the front wheel -- are made of light metals such as aluminum or other light-weight alloys. Lightweight forks are not strong enough to be safe to use with hub motors. Only a steel fork is strong enough to handle the forces that the motor will generate, combined with any road hazards that may be encountered.