There are dozens of good 25Km/h pedelecs. Our advice is to go the nearest good e-bike store and get it from there, because e-bikes may need good support. Only if you like servicing a bike yourself is buying from the Internet a good option. As of Spring 2013, a good benchmark to compare with is the Austrian KTM Amparo also called KTM Severo 8M or the German Kalkhoff Impuls or Agattu series. It has a reliable Panasonic middle motor and a good battery. If you want a more sexy design, try the SMART from the urban car maker of the same name.
For people wanting to push the effects of Statorade to the max, the Australian made Hubsinks can clamp on to your motor shell and provide additional cooling fins to shed heat to ambient air. These fit our new MXUS Cassette motors, and the 9C, Crystalyte H, and many others. These are listed on our new store category for motor cooling mods. And like other small products, we try to  keep a stock of 10mL Statorade syringes on Amazon for easy shipping to US customers. They are sold out now but another shipment is inbound. 
Electric-assisted bicycle operators must follow the same traffic laws as operators of motor vehicles (except those that by their nature would not be relevant). The bicycles may be operated two abreast. Operators must generally ride as close as is practical to the right-hand side of the road (exceptions include when overtaking another vehicle, preparing for a left turn, and to avoid unsafe conditions). The bicycle must be ridden within a single lane. Travel on the shoulder of a road must be in the same direction as the direction of adjacent traffic.
Being member of European Economic Area (EEA), Norway implemented the European Union directive 2002/24/EC. This directive defined legal ebikes for all EU and EEA countries to cycle "with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of 0.25 kW, of which the output is progressively reduced and finally cut off as the vehicle reaches a speed of 25 km/h or if the cyclist stops pedaling." The definition became part of Norwegian vehicle legislation in 2003.[41] A more detailed specification will become effective when the new European ebike product safety standard EN 15194 is published in 2009.
Nebraska defines a Moped as "a bicycle with fully operative pedals for propulsion by human power, an automatic transmission, and a motor with a cylinder capacity not exceeding fifty cubic centimeters which produces no more than two brake horsepower and is capable of propelling the bicycle at a maximum design speed of no more than thirty miles per hour on level ground."[69]
Different gears and ranges of gears are appropriate for different people and styles of cycling. Multi-speed bicycles allow gear selection to suit the circumstances: a cyclist could use a high gear when cycling downhill, a medium gear when cycling on a flat road, and a low gear when cycling uphill. In a lower gear every turn of the pedals leads to fewer rotations of the rear wheel. This allows the energy required to move the same distance to be distributed over more pedal turns, reducing fatigue when riding uphill, with a heavy load, or against strong winds. A higher gear allows a cyclist to make fewer pedal turns to maintain a given speed, but with more effort per turn of the pedals.
The company was founded in 2009 by Tora Harris who graduated from Princeton University with a degree in Mechanical and Aerospace Engineering. While at Princeton, Harris ran track and became a 2-time winner of the NCAA Championship in the High Jump and set several Ivy League track records in the process. Harris went on to win 2 USA National Outdoor Championship Titles and competed in the 2004 Athens Olympic Games.
To qualify as an electric-assisted bicycle under state law they need to have a seat and fully operable pedals for human propulsion, meet federal motor vehicle safety standards, an electric motor that has a power output of not more than 1,000 watts, maximum speed of not more than 20 mph (electric motor and human power combined), disengages or ceases to function when the vehicle’s brakes are applied, two or three wheels
{HIGH-QUALITY MATERIAL & AFFORDABLE PRICE} :The electric bikes adopts High-strength Carbon Steel Frame, the front fork is made of High-strength Carbon Steel and packed with premium comfort shock absorption.Affordable Direct to Consumer Pricing (Sell directly from factory),Why are our bikes often less than half the price of comparable bikes on the market? Because we sell direct to you, the consumer.We ensuring you're always getting the best deal on your electric bike

Did you know that electric bikes can be used for fitness training? Or that they have been scientifically proven to increase the amount of cycling people do? Or that they have proven health and fitness benefits? Well, it’s all true! Apart from being tons of fun, ebikes can be used to improve health and fitness in many ways. Here are our top posts about how ebikes can improve your health and fitness.
Powered by a 250-watt Brose Centerdrive system, the Redux is capable of reaching speeds of up to 28 mph, which comes in handy when dodging traffic. The lithium-ion battery provides enough juice to give the bike a range of up to 80 miles between recharges, making it a great option for daily commuters. Raleigh even outfitted the bike with wide tires which provide stability and traction, even when the road gets wet. Other key features include a 10-speed Shimano crankset and shifters and a built-in LCD screen that displays all the usual information.
Under New Jersey law a motorized bicycle is "a pedal bicycle having a helper motor characterized in that either the maximum piston displacement is less than 50 cc, the motor is rated at no more than 1.5 brake horsepower, or it is powered by an electric drive motor and the bicycle is capable of a maximum speed of no more than 25 miles per hour on a flat surface."[107] This would include E-bikes, meaning they must be titled and registered. However, only Mopeds approved by Motor Vehicle Services can be titled and registered.
In Quebec power-assisted bicycles are often classified similarly to standard pedal bicycles. They do not have to meet the conditions defined within the Canadian Motor Vehicle Safety Regulations (they are not classed as "motor vehicles"), but they do have to comply with federal regulations that define Power Assisted Bicycles. The Quebec Highway Safety Code defines a power-assisted bicycle as a bicycle(2 or 3 wheels that touch the ground) with an electric motor with a maximum power of 500W and a top speed of 32 km/h bearing a specific compliance label permanently attached by the manufacturer[30]. PABs are permitted on the road in the province of Quebec, but riders have to be 14 and over to ride the electric bicycle and if they're under the age of 18, must have a moped or scooter license.
E-bikes use rechargeable batteries, electric motors and some form of control. Battery systems in use include sealed lead-acid (SLA), nickel-cadmium (NiCad), nickel-metal hydride (NiMH) or lithium-ion polymer (Li-ion). Batteries vary according to the voltage, total charge capacity (amp hours), weight, the number of charging cycles before performance degrades, and ability to handle over-voltage charging conditions. The energy costs of operating e-bikes are small, but there can be considerable battery replacement costs. The lifespan of a battery pack varies depending on the type of usage. Shallow discharge/recharge cycles will help extend the overall battery life.
On February 4, 2014, SB997 was introduced by Senator Matt Smith, which seeks to amend PA Vehicle Code to include "Pedalcycle with Electric Assist". In a memo addressed to all senate members, Smith said the definition shall include "bicycles equipped with an electric motor not exceeding 750 watts, weighing not more than 100 pounds, are capable of a maximum speed of not more than 20 mph, and have operable pedals."[128][129]
As long as you can do without some of the perks that pricier models offer—like a detailed display unit, integrated lights, and a torque-sensor motor—the August Live! LS is a solid, stable, comfortable, and really freakin’ cute (have you see those polka-dot fenders?) e-bike. Its 8-speed twist shifter, chopper-style handlebar, Touch Down Geometry (for a more laid-back ride), and three levels of assist keep this bike within the realm of “cruiser.” But with a 250-watt Bafang rear-hub motor, a top pedal-assisted speed of 20 mph, and reliable disc brakes, the August is no joke. It’ll get you to the top of relatively steep climbs without forcing you out of the saddle, and it feels super stable on the way back down. It has a battery range of 20 miles, but that’s enough to take it where it’s happiest: tootling along at the beach, around town, and through the park.
As with all these bikes, the assisted speed is capped at 15mph, but unlike some of them, the Gtech eBike City or its identical (spec-wise) sibling the eBike Sport (this just has a standard frame rather than a step-through one) is light and agile enough for you to be able pedal harder without feeling like the weight is fighting you back down to 15mph. You can even, at a push, use it without the motor on flatter roads.
Controllers for brushless motors: E-bikes require high initial torque and therefore models that use brushless motors typically have Hall sensor commutation for speed and angle measurement. An electronic controller provides assistance as a function of the sensor inputs, the vehicle speed and the required force. The controllers generally allow input by means of potentiometer or Hall Effect twist grip (or thumb-operated lever throttle), closed-loop speed control for precise speed regulation, protection logic for over-voltage, over-current and thermal protection. Bikes with a pedal assist function typically have a disc on the crank shaft featuring a ring of magnets coupled with a Hall sensor giving rise to a series of pulses, the frequency of which is proportional to pedaling speed. The controller uses pulse width modulation to regulate the power to the motor. Sometimes support is provided for regenerative braking but infrequent braking and the low mass of bicycles limits recovered energy. An implementation is described in an application note for a 200 W, 24 V Brushless DC (BLDC) motor.[43]
The Espin is powered by a 350-watt motor that’s rated for trips up to 50 miles (depending on the terrain and assist level). Once depleted, the battery fully charges in roughly five hours. Thankfully, Espin makes it easy to remove the battery, allowing you to quickly recharge it at home or in the office between trips. A backlit LCD control hub displays your basic metrics and battery life while in transit and LED headlights add a touch of light when needed.

With a chain drive transmission, a chainring attached to a crank drives the chain, which in turn rotates the rear wheel via the rear sprocket(s) (cassette or freewheel). There are four gearing options: two-speed hub gear integrated with chain ring, up to 3 chain rings, up to 11 sprockets, hub gear built into rear wheel (3-speed to 14-speed). The most common options are either a rear hub or multiple chain rings combined with multiple sprockets (other combinations of options are possible but less common).


Last year we found a very low-priced (under $600 at Amazon) bike made by Ancheer. Overall, it made some good compromises to get down to the $600 price point but I had some issues with the build quality, the power of the motor, lack of display on the controller and size of the battery. This year a new low-cost Amazon ebike from Rattan seems to have answered many of my concerns.
The E-bike is everything it was advertised to be. It's big and fast and fun to ride especially when riding uphill with pedal assist you have the superhuman ability to get up those tuff climbs that would normally leave you winded and probably walking the bike. The setup was fairly simple however the frame had a couple of serious deep scratch marks in the otherwise impeccable paint job. And even though it's purely cosmetic it was still very disappointing to receive a brand new bike in this condition. It's not clear to me what if anything I can do about it but I still love the bike.
The headlight/horn is completely frail, and prevents folding the bike. However, the wires broke off within two days (60 miles) of riding, so it wasn't an issue after I removed the light completely. Other than that, it's a great electric bike. I put about 24-40 miles per day on it, and it does the job well. I have steep hills during my ride and it really helps with the effort required to go uphill. The gears only go up to 7, which means that when on flat ground, and pedaling for all that I'm worth, I can only get up to 19 mph before the pedals just spin madly. I pass other cyclists when going uphill at nearly twice their speed, but not so much on flat ground or downhill. The rear has no suspension at all, so I bought a $50
Electric motorized bicycles can be power-on-demand, where the motor is activated by a handlebar mounted throttle, and/or a pedelec (from pedal electric), also known as electric assist, where the electric motor is regulated by pedaling. These have a sensor to detect the pedaling speed, the pedaling force, or both. An electronic controller provides assistance as a function of the sensor inputs, the vehicle speed and the required force. Most controllers also provide for manual adjustment.
First, think about what you need your bike for -- if it's just for a short city commute, in among traffic, then consider a smaller frame that's easy to manoeuvre through cars. The GoCycle G3 (right) is impressively nimble and its electric assistance will help propel you up to 15 mph (24 kph). Better yet, it has built-in lights, automatic gears and you can customise the amount of power the motor provides using a phone app.
In a parallel hybrid motorized bicycle, such as the aforementioned 1897 invention by Hosea W. Libbey, human and motor inputs are mechanically coupled either in the bottom bracket, the rear or the front wheel, whereas in a (mechanical) series hybrid cycle, the human and motor inputs are coupled through differential gearing. In an (electronic) series hybrid cycle, human power is converted into electricity and is fed directly into the motor and mostly additional electricity is supplied from a battery.
Maybe the most confusing legal issue facing e-bike riders today is the difference between a bike lane and bike path. A bike lane is a marked section of roadway shared with motor vehicles. Bike paths pretty much universally prohibit the use of motorized vehicles. Still, you will need to research your area. As an example: “A path near our office specifically says “no motorized bicycles.” Yet, when we tracked down an employee who claimed to work enforcement on the path, he said that our e-bike was allowed.”8
The two most common types of hub motors used in electric bicycles are brushed and brushless. Many configurations are available, 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 using chain drive, belt drive, hub motors or friction drive. BLDC hub motors are a common modern design. The motor is built into the wheel hub itself, and the stator fixed solidly to the axle, and the magnets attached to and rotating with the wheel. The bicycle wheel hub is the motor. The power levels of motors used are influenced by available legal categories and are often, but not always limited to under 750 watts.

At Volt, when we sell an ebike, we like to keep in touch with our customers. This is not only to find out how their electric bike is performing and if they are happy with it, but also to learn how they use it. Many have impressive stories to tell. We have heard from people using Volt bikes in the most diverse ways and places, from the Scottish Highlands to central London.
Photo: Zap Electric's power-assist kit turns a conventional bike into an electric one. There's a bolt-on DC electric motor (weighing just over 3kg or 7lb) just above the back wheel, behind the police officer's foot, pressing against the tire and driving it by simple friction. The motor's powered by a compact lead-acid battery (weighing about 5.5 kg or 12 lb) inside a protective nylon bag. This kit adds quite bit of weight to the bike, but gives extra range and speed when needed. Photo taken in Santa Rosa, California by Rick Tang courtesy of US DOE/NREL.

I bought the 52v 13ah for my 1000w BBSHD build and it is working great. My bike tears it up pretty good with this battery pack. Hopefully I don't run into any problems but so far so good. One thing I learned the hard way - if you use a 52v pack with the 1000w bbshd your battery meter will no longer be accurate. That was one tough ride home with my heavy fat bike!
There is however still confusion over the various legislations involving Electric Bicycles. This stems from the fact that while places like the US and Canada offer some Federal regulation, the legality of road use is left to the various States or Provinces and then complicated further by municipal laws and restrictions. Further more there are a range of classifications and terms describing them, "Power-assisted bicycle" (Canada) or "Power assisted cycle" (United Kingdom) or ”Electric pedal assisted cycles” (European Union) or simply "electric bicycles", and as such in some cases have varying laws according to their respective classifications in some places.

The battery is the pedelec’s power source. It supplies the motor with the electrical energy that is required to provide power assistance when cycling. So it is hardly surprising that there is frequent discussion and “talking shop” about the eBike’s battery in particular. What is the difference between batteries? How far can you go on a fully charged battery? What do you have to remember about storage? Thomas Raica, head of technical customer application, here provides information and advice.

Some argue, that an ebike should have some kind of front suspension, i.e. be able to cope with potholes at higher speed or off-road conditions. However, in countries with flat roads (e.g. Switzerland, Germany or Holland) you don't need that extra weight for extra price if you stay on roads and/or drive slowly in difficult terrain. Some makes (like the Stromer) let you choose.

While we're still fairly new to the solar ebike game, Mark is among the (suprisingly numerous) Grin customers who've been thinking about and experimenting with solar bikes for many years. After he shared pictures of his latest project and mentioned his round the world touring ambitions, we thought we had to do a small feature on this guy. A quick last minute trip to Maker Faire was arranged to meet up, and here we present, Mark Havran:
State law defines a motorized pedalcycle as a motor-driven cycle equipped with operable pedals, a motor rated at no more than 1.5 brake horsepower, a cylinder capacity not exceeding 50 cubic centimeters, an automatic transmission, and a maximum design speed of no more than 25 miles per hour.[55] Subchapter J of Publication 45 spells out the vehicle requirements in full.
I eventually got used to it over time, but at first having both kids behind me made the bike feel like it would sway to or fro perilously. I think it was just too much weight to navigate safely, and would be fine with younger kids that didn’t come close to the 120-pound weight limit for the rear cargo area. Overall I’m still a bit partial to a box-style bike if I’m hauling multiple kids and want to be able to see what they’re doing.
To qualify as an electric-assisted bicycle under state law they need to have a seat and fully operable pedals for human propulsion, meet federal motor vehicle safety standards, an electric motor that has a power output of not more than 1,000 watts, maximum speed of not more than 20 mph (electric motor and human power combined), disengages or ceases to function when the vehicle’s brakes are applied, two or three wheels
Electric-assist and other "motorized bicycles"[86] do not need to be inspected, do not require a license, and do not require registration. The vehicle must meet all of the following criteria: a post mounted seat for each person it is designed to carry, two or three wheels which contact the ground, fully operative pedals, wheels at least 16 inches in diameter and a motor not capable of propelling the device at more than 20 mph on level ground. The driver does not need a license, but must be at least 16 years old. DC law prohibits motorized bicycles from traveling anywhere on the sidewalk or in the bike lanes. DC Regulation 18-1201.18 provides: "Except as otherwise permitted for a motor vehicle, no person shall operate a motorized bicycle on any sidewalk or any off-street bikepath or bicycle route within the District. This prohibition shall apply even though the motorized bicycle is being operated solely by human power." So, if cars are prohibited in a particular place, motor-assisted bikes are also prohibited.[87]
What an experience. I really had no idea what to expect when I first got on. The ride was smooth, and the assisting function was excellent and seamless. It is not like a motorcycle, it is just like a bike with some extra help. I felt completely safe on this bike, as well as comfortable in the seat. Especially in San Francisco with all the hills, going up the ramp felt like I was moving on a flat surface still. For commuters who might be worried about having to change clothes during an arduous commute in on their bike, fear not. This bike makes everything easy, and simple enough that you could ride to work in your work clothes and not fear getting too hot and sweaty. For those who have switched to the bike to decrease their impact on the environment, this bike is a must. Get there fast,

Track bicycles do not have brakes, because all riders ride in the same direction around a track which does not necessitate sharp deceleration. Track riders are still able to slow down because all track bicycles are fixed-gear, meaning that there is no freewheel. Without a freewheel, coasting is impossible, so when the rear wheel is moving, the cranks are moving. To slow down, the rider applies resistance to the pedals, acting as a braking system which can be as effective as a conventional rear wheel brake, but not as effective as a front wheel brake.[51]
There are a variety of gadgets in the market for a hunter. These gadgets have made the hunting experience a lot easier and better. However, not everyone requires everything available in the market. It’s from your experience you learn what is best for you. Let’s look at some important gadgets you may want to have on your next hunting trip.   Electric Hunting Bikes Electric hunting bikes are a better bet than the dirt bikes or ATV’s. It makes lesser noise than the other modes of transport so you don't spook the wildlife. You can carry your gadgets and hunting...

Electric-assist and other "motorized bicycles"[86] do not need to be inspected, do not require a license, and do not require registration. The vehicle must meet all of the following criteria: a post mounted seat for each person it is designed to carry, two or three wheels which contact the ground, fully operative pedals, wheels at least 16 inches in diameter and a motor not capable of propelling the device at more than 20 mph on level ground. The driver does not need a license, but must be at least 16 years old. DC law prohibits motorized bicycles from traveling anywhere on the sidewalk or in the bike lanes. DC Regulation 18-1201.18 provides: "Except as otherwise permitted for a motor vehicle, no person shall operate a motorized bicycle on any sidewalk or any off-street bikepath or bicycle route within the District. This prohibition shall apply even though the motorized bicycle is being operated solely by human power." So, if cars are prohibited in a particular place, motor-assisted bikes are also prohibited.[87]


Built around a heavy-duty alloy frame, the GSD eschews many of the traits of other cargo bikes: long wheelbases, bigger wheels, and especially, an unwieldy ride. Yet it boasts an extensive capacity, nimble handling—even fully loaded, thanks to a short wheelbase and 20-inch wheels—and enduring range in a package not much bigger than most non-cargo e-bikes. The stout frame holds a 250-watt Bosch motor that gives up to 275 percent of your power back to the pedals and reaches 20 mph. The GSD has room for two battery packs, extending the batteries’ combined range to a claimed 150 miles and making the Tern one of the longest-lasting e-bikes on the market. A laundry list of accessories and a (claimed) 396-pound carrying capacity round out the GSD’s status as an epic day-tripper.
And let’s not forget the economic advantages of owning an e-bike. The annual cost of running a new family car is, on average, about $9,000 per year. Running an electric bike costs around $400 per year. And while filling a gas tank costs around $30, recharging an electric bike battery costs only about 50 cents. A tank of gas may get you further, but not 60 times further!
Power-assist: Also known as pedal-assist bikes, these are the bicycle equivalents of hybrid cars: they're designed to be pedaled quite a lot of the time and electrically powered either when you're tired or when you feel like a bit of electric help (when you're going up hill, for example). Unlike full-power bikes, they don't have hub motors; instead, there's a separate electric motor mounted near the rear wheel and driving it either through the gear sprocket or simply by pressing against the rear tire. Where a hub motor is difficult or impossible to pedal without any power (because you're effectively turning it into a generator), power-assist motors turn easily with little or no resistance when you pedal. That gives power-assist bikes much greater range than hub-motor ones (as much as 80–145km or 50–90 miles).
E-bikes are zero-emissions vehicles, as they emit no combustion by-products. However, the environmental effects of electricity generation and power distribution and of manufacturing and disposing of (limited life) high storage density batteries must be taken into account. Even with these issues considered, e-bikes are claimed to have a significantly lower environmental impact than conventional automobiles, and are generally seen as environmentally desirable in an urban environment.[65]

Under New Jersey law a motorized bicycle is "a pedal bicycle having a helper motor characterized in that either the maximum piston displacement is less than 50 cc, the motor is rated at no more than 1.5 brake horsepower, or it is powered by an electric drive motor and the bicycle is capable of a maximum speed of no more than 25 miles per hour on a flat surface."[107] This would include E-bikes, meaning they must be titled and registered. However, only Mopeds approved by Motor Vehicle Services can be titled and registered.


But two other concerns are also front and center when it comes to biking: cost and convenience. Not many people have showers at their places of employment, and who wants to show up to work coated in sweat and stinky for the rest of the day? Electric bikes solve the convenience problem by making the process almost effortless; you can bike for miles—even up and down hills—without breaking a sweat.
To operate a motorized/electric-assisted bicycle on the streets or highways a person must have a valid driver’s license or a motorized bicycle permit. A person under the age of 16 operating a motorized/electric-assisted bicycle under a motorized bicycle permit is subject to restrictions of no passengers (a parent or guardian my ride if the motorized/electric assisted bicycle is equipped with a seat and footrests for a passenger), no night driving, driving on any highway marked as an interstate, must wear a helmet, foot rests for passengers (if designed for passenger(s). A motorized bicycle permit is available to persons of at least 15 years of age who have passed the motorized bicycle test or passed a motorized bicycle course. A motorized bicycle would need the same coverage as a motorcycle would in this state. An electric-assisted bicycle would not need coverage.
In built up cities around the world, urban planning uses cycling infrastructure like bikeways to reduce traffic congestion and air pollution.[59] A number of cities around the world have implemented schemes known as bicycle sharing systems or community bicycle programs.[60][61] The first of these was the White Bicycle plan in Amsterdam in 1965. It was followed by yellow bicycles in La Rochelle and green bicycles in Cambridge. These initiatives complement public transport systems and offer an alternative to motorized traffic to help reduce congestion and pollution.[62] In Europe, especially in the Netherlands and parts of Germany and Denmark, bicycle commuting is common. In Copenhagen, a cyclists' organization runs a Cycling Embassy that promotes biking for commuting and sightseeing. The United Kingdom has a tax break scheme (IR 176) that allows employees to buy a new bicycle tax free to use for commuting.[63]

Several bills have been sponsored to legalize electric bicycles for use on NYS roads, and several have overwhelmingly passed at the committee level, but none of these initiatives has been able to be heard and then passed in the New York State Senate, until 2015. The latest bill S3997, "An act to amend the vehicle and traffic law, in relation to the definition of electric assisted bicycle. Clarifying the vehicle and traffic law to define electric assisted bicycles; establish that electric assisted bicycles, as defined, are bicycles, not motor vehicles; and establish safety and operational criteria for their use." has passed in the Senate for the first time ever in 2015.[116] The related Assembly bill A233 was not brought to a vote in the assembly even though it had passed with little issue in prior years.[117]
If you're more concerned with conquering the countryside than the commute, Cyclotricity's Stealth is the one for you. It's a full-size mountain bike, with aggressive tyres and suspension on the front forks to absorb the rocks and bumps on the trails. It's comfortable to ride, and its motor can either give you assistance while you ride, or you can just hit the throttle to rocket over hills with no effort on your part.
In the theoretical electric bike we considered up above, we had the dynamo/motor driving the back wheel directly, simply by pressing on the tire. Most electric bikes work a different way. They have compact electric motors built into the hub of the back or front wheel (or mounted in the center of the bike and connected to the pedal sprocket). Take a look at the hub of an electric bike and probably you'll see it's much fatter and bulkier than on a normal bike. You can read more about how these motors work in our main article about hub motors.
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