A motorized bicycle is a bicycle with an attached motor used to assist with pedaling. Generally considered to be a vehicle, sometimes as a motor vehicle or a class of hybrid vehicle, motorized bicycles are usually powered by electric motors or small internal combustion engines. Some can be propelled by the motor alone if the rider chooses not to pedal, while in others the motor will only run if the rider pedals. Different regulatory authorities use a variety of names and classifications.
Some early motorized bicycles were powered by internal combustion (IC) engines whereas some utilized electric motors. With lighter batteries and better storage density, the electric motor has recently seen an increase in popularity.
Motorized bicycles are distinguished from motorcycles by being capable of being powered by pedals alone if required. The actual usage of the pedals varies widely according to the type of vehicle. Those known as mopeds mostly have pedals for emergency use or because of legal requirements and these are not normally used. Those known as power-assist bikes have the pedals as the main form of propulsion with the motor used to give a bit of extra speed, especially uphill. Many motorized bicycles are based on standard bicycle frame designs and technologies, although the modifications to the design to support motorization may be extensive.
In countries where there is a strong bicycle culture (notably in Asia), the motorized bicycle is particularly popular; in 1996 Shanghai had 370,000 motorized bicycles and 470,000 other vehicles.
The origins of the motorized bicycle can be traced back to the latter part of the 19th century when experimenters began attaching steam engines to stock tricycles and quadracycles. This moved into attempts to fit the newly-invented internal combustion engine to the bicycle form.
Development diverged into two distinct streams: motorcycles, which are powered solely by their engines, and motorized bicycles as defined above. The closeness of the two forms in early years is demonstrated by Félix Millet's machines of 1892/93 and on. These had both pedals and an ingenious fixed crankshaft rotary engine built into the back wheel. Within a few years motorized bicycles and motorcycles were recognisably divergent, with for example early motorcycles being longer, heavier and with a markedly different riding position from that of a contemporary pedal cycle. Later, development forked again with the advent of mopeds, small motorcycles fitted with pedals that can be used as a starting aid but which cannot, practically, be ridden under pedal power alone. This development appears to have been largely in order to exploit ambiguities between the regulatory framework for bicycles, powered bicycles and motorcycles - in jurisdictions where pedals were not required to meet the legal framework they were often simply omitted on otherwise identical models.
In the case of motorized bicycles, too, there were soon two parallel streams of development: motor assistance as an addition to existing machines, and purpose-built motor-assisted bicycles like the Darn and VéloSoleX, with stronger frames and sometimes with only token ability to be wholly human powered. In these cases some assert that the product is more formally a motorcycle or moped than a motorized bicycle, and some jurisdictions also take this view.
Modern motorized bicycles follow both trends, with conversions being applied by hobbyists as well as commercial manufacturers. Hub motors in particular facilitate after market conversion, being built into the wheel and not requiring modifications to the drivetrain or frame, as well as having a low centre of gravity. Converting bicycles or tricycles has proven useful for some people with physical disabilities such as arthritis. The strength of tricycles is that they will balance even while stationary, but some people find it harder to drive a tricycle and claim it lacks agility. Portability is also compromised compared to bicycles.
The modern electric bicycle is true to the concept of a pedal bicycle with assisting propulsion, being ridable without power. Batteries have finite capacity, which means that the hybrid human / electric power mix is much more likely to be emphasised than is the case with an internal combustion (IC) engine. Electric bicycles are gaining acceptance, especially in Europe and Asia, in response to increasing traffic congestion, an ageing population and concern about the environment. Electric vehicle conversion – converting conventionally-powered vehicles to electric or hybrid vehicles – is also increasingly common.
Motorized bicycles' popularity has waxed and waned largely in response to local regulatory requirements. For example, the French "vélomoteur" could be ridden by young riders without need for a license, making it very popular during the 1960s and 1970s.
Autocycle manufacturers were well established in countries such as Britain and Australia before the second world war, but the hiatus of the war appears to have set the market back, although the American bolt-on Whizzer continued until 1962. The motorized bicycle saw a resurgence of popularity in Britain during the 1950s and such bolt-on motors as the Cyclaid and the Cyclemaster motor wheel saw brief periods of immense popularity. Elsewhere in Europe the motorized bicycle continued to be popular. The Italian, Vincenti Piatti had designed a 50 cc engine for driving portable lathes and this was also used to in the form of the Mini Motore to power bicycles. Piatti later licensed the design to Trojan for production in Britain as the Trojan Minimotor. Production of The French VELOSOLEX began in 1946 and continued until 1988. After French production ceased, the VELOSOLEX continued to be produced in China and Hungary. In 2003 production ceased in Hungary. Today production continues in China and has restarted in France. Velosolex America is the company that markets the VELOSOLEX worldwide.
The legal definition and status of motorized bicycles varies by jurisdiction. Legal terms for motorized bicycles include "Power Assisted Bicycle (PAB)" (Canada), "Power assisted cycle" (United Kingdom), or (commonly) "electric bicycle". The UK legal requirements for a product to be classed as an Electric Bike include the following: weight must be 40kg or less, motor rating not over 200 watts continuous power output, motor powered speed not exceeding 15mph and the cycle must have working pedals.
Generally they are considered vehicles (like motorcycles and pedal cycles), so are subject to the same rules of the road. In a few jurisdictions, motorized bicycles must be licensed and display vehicle registration plates. Regulations may define maximum power output and for electric bikes may or may not require an interlock to prevent use of power when the rider is not pedalling. In some cases regulatory requirements have been complicated by lobbying in respect of the Segway HT.
Historically, internal combustion (IC) engines dominated the motorized bicycle market, but most current models use electric motors.
Power can be applied in a number of ways:
The 1900 Singer Motor Wheel was a wheel incorporating a small IC engine that could be substituted for the front wheel of a bicycle, while the 1914 Smith Motor Wheel was attached to the rear of a bicycle by means of an outrigger arm, a design later taken up by Briggs & Stratton.
The VéloSoleX, probably the last large-scale IC-powered motorized bicycle, used friction drive to the front wheel. The last volume manufactured in-wheel IC engine was used on the Honda P50 moped which ceased production around 1968.
Tanaka bolt-on bike motors (branded Bike Bug, Aqua Bug, Tas Spitz, Sears Free Spirit, and Little Devil) were popular through the 1960s and 1970s, and are gaining a renewed following thanks to some rediscovered kits.
In the late-2000s, the RevoPower Wheel returned to a concept similar to the 1900 Singer Motor Wheel, again providing an engine that would go in place of the ordinary front wheel of the bicycle to provide extra power.
There are many possible types of electric motorized bicycles with several technologies available for electric motors, varying in cost and complexity; direct-drive and geared motor units are both used. An electric power-assist system may be added to almost any pedal cycle. Chain drive and hub motors are both common, friction drive less so. Most hub motors are in the 250w to 450w category.
Electric bicycles are generally powered by rechargeable batteries. These are normally charged from the utility supply (mains), with perhaps the option of using the motor to effect regenerative braking or charging while being pedaled or rolling downhill. There are also experiments with recharging via solar panels and, to a lesser extent, other alternative energy sources such as fuel cells. Most modern electric bikes use technologies such as rare earth magnets, pulse width modulated power electronic control and regenerative braking to improve efficiency. Batteries are usually either lead-acid, NiCd, NiMH or Li-ion. Lithium ion polymer batteries are now beginning to be used as well, offering the advantage of lighter weight for the same energy storage capability but at a higher cost.
Electric motorized bicycles are either power-on-demand, where the motor is activated by a handlebar mounted throttle, or pedelec (from pedal electric), where the electric motor is regulated by pedaling. These may have a mechanism such as a crank sensor to detect when the user is pedalling, or a more sophisticated torque sensor. The degree of assistance can usually be controlled to optimize battery life.
Range is a key consideration with electric bikes, and is affected by factors such as motor efficiency, battery capacity, efficiency of the driving electronics, aerodynamics, hills and weight of the bike and rider combined. The range of an electric bike is usually stated as somewhere between 7km (uphill on electric power only) to 70km (minimum assistance).
Individuals have built bicycles powered by steam and air engines, and there is at least one example of a jet propelled bicycle. No large-scale manufacture of any of these is known.