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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. This bypasses the need for a transmission, so 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 since the late 19th century. They originally were conceived for use in automobiles, but modern hub motors are used almost exclusively on electric bicycles. Motorized bicycles are more common in Asia than in other parts of the world, but they have continued to grow in popularity elsewhere because of technological advances. Some motorized bicycles are manufactured, but it can sometimes be cheaper for a hub motor to be installed 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.
A motorized bicycle that is equipped with a hub motor will most often also have functioning pedals. If the battery that runs the hub motor runs out, the bike still will need propulsion. Legal regulations in some places might also prohibit the use of motorized vehicles that are not registered.
Hub motors typically 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, the rider's weight and weather, an electric bicycle can have a range as short as 4.3 miles (7 km) or as long as 43.5 miles (70 km).
When converting a pedaled bicycle to electric, the hub motor usually is installed on the front wheel. The motor produces high levels of torque on this part of the bike, and it is important for the person doing the conversion to make sure that the frame of the bike can stand up to these increased forces. Many bicycle forks — the parts that mount onto the front wheel — are made of light metals such as aluminum or other lightweight alloys. Lightweight forks are not strong enough to be safe for 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 might be encountered.
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