None of this would matter if the VanMoof Electrified S2 (and its close relative the X2) wasn't fun to ride, but it is a blast. Like the Brompton, it pulls off the neat trick of powering you along but giving the illusion that you're doing the work, reacting quickly and cleverly to the speed of your pedalling and the difficulty of any incline you're on. 
Like most electric bikes, the Rad Wagon is also fairly heavy, weighing 72 pounds. The last drawback is that it comes in only one frame size (which I imagine helps to keep costs lower) that fits rider heights between 5 foot 2 inches and 6 foot 2 inches. My 6 foot 4 husband, however, can ride the bike just fine, so there’s some wiggle room to this range.
If you have dynamo-powered bicycle lights, you already own an electric-powered bicycle! Consider: as you pump your legs up and down on the pedals, you make the wheels rotate. A small dynamo (generator) mounted on the rear wheel produces a tiny current of electricity that keeps your back safety lamp lit in the dark. Now suppose you could run this process backward. What if you removed the lamp and replaced it with a large battery. The battery would kick out a steady electric current, driving the dynamo in reverse so that it spun around like an electric motor. As the dynamo/motor turned, it would rotate the tire and make the bike go along without any help from your pedaling. Hey presto: an electric bike! It may sound a bit far-fetched, but this is more or less exactly how electric bikes work.
Because e-bikes are capable of greater speeds for longer periods of time than standard bikes, you want extra control. Wider tires provide traction and some bump absorption with little penalty. You also want strong brakes to slow you (and all that extra weight) easily. It’s worth looking at the quality of the brakes and investing in bikes with better ones if you can.
The Bosch Performance CX is still one of the most popular motors on the market. It’s synonymous with reliability, but it’s getting on in years. The newly presented Active Line looks like a glimpse into Bosch’s future: it is more compact, lighter, has less internal resistance, and uses a large chainring. It can only be a matter of time before Bosch releases a new performance motor.
E-bikes can boost bike usage, offer health benefits and use “an order of magnitude less carbon dioxide than a car traveling the same distance,” according to a 2016 research review published in the journal Transport Reviews.  In fact, access to an e-bike increased cycling trips and distances traveled – and nearly doubled the bike as a mode of transportation, observed one Norwegian study.
The motor isn’t insanely powerful, but it gets you up to full speed quickly enough. I never felt like the bike was underpowered. The motor does make more noise than a lot of other hub motor bikes I’ve ridden though. There’s a definite whirrr to the motor caused by the internal plastic gears. While all geared motors will have some level of gear noise, this one stuck out more to me than others.
The frame of an electric bike also has to be slightly different. The main part of the frame (the bit that supports your weight) is usually made from lightweight aluminum alloy: the lighter the frame, the lighter the weight of the bike overall, and the further it can travel before you need to recharge the batteries. The spokes on the wheel also have to be stronger than the thin spokes on a traditional bicycle. That's because the electric motor in the hub spins the wheel with a lot of turning force (known as torque) and, if the spokes were ordinary lightweight ones, they could bend or buckle.

"Electric-assisted bicycle" means a bicycle with two or three wheels, a saddle, fully operative pedals for human propulsion, and an electric motor. The electric-assisted bicycle's electric motor must have a power output of no more than one thousand watts, be incapable of propelling the device at a speed of more than twenty miles per hour on level ground, and be incapable of further increasing the speed of the device when human power alone is used to propel the device beyond twenty miles per hour.[66]
Simple, convenient, cheap, and economical—bicycles are one of the world's favorite forms of transportation. But they're not for everyone. They can be hard to pedal up and down hills or with heavy loads, and elderly or disabled people may find them impossible to manage. In the last few years, a new generation of electric bicycles has begun to revolutionize our idea of environmentally friendly transportation. These new cycles have all the convenience of cars with all the simple economy of ordinary cycles. Let's take a closer look at how they work.