I do not recommend hacking a bike into s-pedelec, i.e. make a 25km/h bike go at 45 or faster. If you have an accident you will be in trouble. Just get a legal version. In addition you will have good insurance. Of course, in countries like France or the UK that so far do not know S-Pedelecs, you will have to make a difficult moral choice.... At least, make sure that your rig is safe...
The word bicycle first appeared in English print in The Daily News in 1868, to describe "Bysicles and trysicles" on the "Champs Elysées and Bois de Boulogne".[11] The word was first used in 1847 in a French publication to describe an unidentified two-wheeled vehicle, possibly a carriage.[11] The design of the bicycle was an advance on the velocipede, although the words were used with some degree of overlap for a time.[11][12]
From the beginning and still today, bicycles have been and are employed for many uses. In a utilitarian way, bicycles are used for transportation, bicycle commuting, and utility cycling. It can be used as a 'work horse', used by mail carriers, paramedics, police, messengers, and general delivery services. Military uses of bicycles include communications, reconnaissance, troop movement, supply of provisions, and patrol. See also: bicycle infantry.

A "class 1 electric bicycle," or "low-speed pedal-assisted electric bicycle," is a bicycle equipped with a motor that provides assistance only when the rider is pedaling, and that ceases to provide assistance when the bicycle reaches the speed of 20 miles per hour. (2) A "class 2 electric bicycle," or "low-speed throttle-assisted electric bicycle," is a bicycle equipped with a motor that may be used exclusively to propel the bicycle, and that is not capable of providing assistance when the bicycle reaches the speed of 20 miles per hour. A "class 3 electric bicycle," or "speed pedal-assisted electric bicycle," is a bicycle equipped with a motor that provides assistance only when the rider is pedaling, (no throttle) and that ceases to provide assistance when the bicycle reaches the speed of 28 miles per hour, and equipped with a speedometer. Local government ordinances are allowed to permit or ban any class of electric bicycles on dedicated bicycle paths and trails, with Class 1 & 2 permitted, and Class 3 banned, by default.
Oklahoma defines an Electric-Assisted Bicycle in 47 O.S. 1-104 [122] as "Two or three wheels; and Fully operative pedals for human propulsion and equipped with an electric motor with a power output not to exceed one thousand (1,000) watts, incapable of propelling the device at a speed of more than thirty (30) miles per hour on level ground, and incapable of further increasing the speed of the device when human power alone is used to propel the device at a speed of thirty (30) miles per hour or more. An electric-assisted bicycle shall meet the requirements of the Federal Motor Vehicle Safety Standards as set forth in federal regulations and shall operate in such a manner that the electric motor disengages or ceases to function when the brakes are applied."

Because the power is applied through the chain and sprocket, power is typically limited to around 250–500 watts to protect against fast wear on the drivetrain. An electric mid-drive combined with an internal gear hub at the back hub may require care due to the lack of a clutch mechanism to soften the shock to the gears at the moment of re-engagement. A continuously variable transmission or a fully automatic internal gear hub may reduce the shocks due to the viscosity of oils used for liquid coupling instead of the mechanical couplings of the conventional internal gear hubs.
Electric bicycle fits under the definition of "moped" under Kentucky law. You don't need tag or insurance, but you need a driver's license. "Moped" means either a motorized bicycle whose frame design may include one (1) or more horizontal crossbars supporting a fuel tank so long as it also has pedals, or a motorized bicycle with a step-through type frame which may or may not have pedals rated no more than two (2) brake horsepower, a cylinder capacity not exceeding fifty (50) cubic centimeters, an automatic transmission not requiring clutching or shifting by the operator after the drive system is engaged, and capable of a maximum speed of not more than thirty (30) miles per hour[94][95] Helmets are required.
State laws tend to intermix the source of power as either gasoline ICE or electric drive. This is unfortunate because that neutralizes the environmental advantage of an ebike over an ICE moped. It also misrepresents the contrast in power output levels between an ICE and electric motor system. 50cc gas mopeds/scooters have a 2.5-4 HP rating, while the 20+ mph electric bikes will be 1-2hp, and ride much closer to a normal bicycle compared to a gas powered, 2.5hp moped. E-mopeds will weigh 55-70lbs. Gas mopeds and scooters are typically over 120lbs. E-mopeds are still electric bikes that get valuable power assist from human pedal effort and are usually much quieter.

The environmental effects involved in recharging the batteries can of course be reduced. The small size of the battery pack on an e-bike, relative to the larger pack used in an electric car, makes them very good candidates for charging via solar power or other renewable energy resources. Sanyo capitalized on this benefit when it set up "solar parking lots", in which e-bike riders can charge their vehicles while parked under photovoltaic panels.[66]
The federal Consumer Product Safety Act defines a "low speed electric bicycle" as a two or three wheeled vehicle with fully operable pedals, a top speed when powered solely by the motor under 20 mph (32 km/h) and an electric motor that produces less than 750 W (1.01 hp). The Act authorizes the Consumer Product Safety Commission to protect people who ride low-speed electric vehicles by issuing necessary safety regulations.[63] The rules for e-bikes on public roads, sidewalks, and pathways are under state jurisdiction, and vary.
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They also served to teach the industrial models later adopted, including mechanization and mass production (later copied and adopted by Ford and General Motors),[76][77][78] vertical integration[77] (also later copied and adopted by Ford), aggressive advertising[79] (as much as 10% of all advertising in U.S. periodicals in 1898 was by bicycle makers),[80] lobbying for better roads (which had the side benefit of acting as advertising, and of improving sales by providing more places to ride),[78] all first practiced by Pope.[78] In addition, bicycle makers adopted the annual model change[76][81] (later derided as planned obsolescence, and usually credited to General Motors), which proved very successful.[82]

During testing—and unlike some of the other bikes I’ve tried—this range held true, with the Rad Wagon handling a 20-plus mile round trip with ease. This is helped by a regenerative braking system that automatically charges the battery whenever you engage the brake levels. It’s also relatively quick to charge back up—taking around four hours in my garage—although Rad Power reports that average time is five to six hours.

Even with cheaper or heavier bikes, once you accept that you are really meant to pedal gently and let the motor do the work, non-speed freaks will get into it. E-bikes are great for commuting and for places that aren't pancake flat. They'll pull you away from the lights quickly, iron out hills and stop you getting sweaty, so you can bin the Lycra and ride in jeans, a suit, or a winter coat.
By Max Shumpert: This article has been updated to reflect the most accurate information regarding best e-bikes available for those who are interested in new technology combined with traditional bikes. The best 5 available have changed, and information has been added to assist individuals in finding the best electric bicycles currently available on the market. The FAQ has also been updated.
Perhaps the cleverest thing of all about the Electric Brompton is that despite all the extra stuff, it folds up exactly the same as the non-powered variety. It's so simple, and unlike certain folding bikes we could mention, what you're left with is a genuinely small thing, rather than something that's about the size of a bike with the front wheel taken off. 
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