How Do Electric Bikes Work?

Whether you're considering buying an eBike or just want to know more about how they work, we've got you covered

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reviewed by Rory McAllister
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Unless you’re a mechanical engineer, a physicist, or in the industry, you might be asking yourself: How do electric bikes work?

In simple terms, an electric bike (or eBike) works by using a motor to assist you while you pedal. This motor is powered by a rechargeable battery mounted somewhere on the bike.

However, there’s a lot more to it than that!

In this article, we’ll be walking you through key concepts in explaining how electric bikes work, including how they know when to provide power, how they adjust to how much power the rider is applying to the pedals, and some of the key design choices that affect how eBikes work.

Let’s get started!

Graphic showing how an electric bike works on a blue background.
Mid-drive electric bike with Bosch motor.

What Is An Electric Bike?

If you’re unfamiliar with the concept, you might be picturing something more similar to a two-wheeled electric car, whereby the bike can power itself without any mechanical energy supplied by the rider.

But, don’t be fooled, the name “electric bike” refers to the fact that it uses electrical energy supplied by a battery to create a “power assist”. As you pedal, the power your legs supply will be supplemented by the battery-powered motor.

Of course, a two-wheeled machine that propels you on its own does exist – but would likely be classified as an electric motorbike, rather than an electric bike.

Most electric bikes have different settings that allow you to choose how much extra electric power the battery will supply, based on how hard you are pedaling. Using the e-bike on the highest setting of electric assist will reduce the battery range of the eBike.

Most electric bicycles look just like regular bikes but with a slightly thicker downtube or wider hubs to house the battery. They come in all shapes and sizes, and you can get an electric bike suited to any discipline.

Electric road bikes, gravel bikes, electric mountain bikes, fat tire bikes, commuter bikes, urban bikes, cargo bikes, hybrid bikes, and folding bikes are all available for purchase and will be the first decision you need to make before you go and invest in an electric bike.

Of course, the quality of electric bikes can also vary significantly.

There are the same variations as with mechanical bikes, such as groupsets, materials, weight, aerodynamic qualities, and strength, but also there’s variation in the quality of the batteries, which might make a difference to the possible range, charge time, battery life, or power assistance.

Close-up of the frame of an eBike.

How Do Electric Bikes Work?

So, we know what electric bikes are and what they do, but how do eBikes work?

An electric bike works by supplying electricity stored in a rechargeable battery to a motor, which will assist the rider by providing extra power while you pedal.

Electric Bike Batteries, Sensors, and E-Bike Motors

An electric bike will house a compact, lightweight (typically) lithium-ion battery either inside the frame or attached to the outside.

The battery capacity must be high relative to its size, and can’t be so heavy that it might affect the eBike’s maneuverability. Typical eBike batteries and motors can output around 350-500 Watts.

A torque sensor usually located in the pedals, cranks, or chainset measures how hard the cyclist is turning the pedals and adjusts the pedal assist power supplied by the battery accordingly.

The rider can usually also control how much extra pedal power is supplied relative to how hard they turn the pedals by adjusting the eBike’s settings.

The electrical energy is supplied by the battery to a motor, which converts it into rotational kinetic energy, forcing it to rotate.

The Controls

On almost all electric bikes, different settings allow the rider to select the amount of power assistance.

These controls are usually located either on the handlebars or on the top tube near the joint with the head tube for easy access while riding.

The settings will have often a “no power assist mode” which could be selected if you’re keen to get some juices flowing in the legs, you’re on a big descent, or you’re running low on power and want to save the battery for a steep hill, for example.

Mid-Drive Vs Hub Motor

How do electric bikes work? This graphic shows a mid-drive electric bike on a brown background.
A mid-drive electric bike.

The electric bike motor is usually placed either in the bottom bracket area (a mid-drive electric bike) or in the hub of one or both of the bike’s wheels (hub-drive electric bikes).

A mid-drive bike will supply the rotational kinetic energy directly to the pedals: this means that your assistance comes directly at the point of contact, and the additional motor power assistance runs through the drivetrain before reaching the wheels and the contact with the road.

A hub-drive electric bike supplies the rotational power to the wheels themselves, and forces the wheels to rotate faster than they would have given the amount of power supplied through the pedals by the rider.

A hub-driven electric bike on a pink background.
A hub-driven electric bike.

A hub motor can be placed on either wheel, but a rear hub motor is far more common since, just like in a car, a front hub motor will affect the handling far more. All-wheel drive (AWD) or “2×2” electric bikes are also available.

Although a mid-drive motor will almost always make use of a torque sensor to measure power output by the rider, a hub motor usually uses a cadence sensor (how fast the pedals turn, rather than how hard the rider is turning them) to determine the power assistance required.

However, this comes with a couple of clear downsides. Firstly, a hub-driven motor will supply more constant power assistance than a mid-drive motor (due to the different sensing systems) which means the assistance is less sensitive to your input.

Some people claim that hub motors will affect your handling more due to adding “rotational weight” – though this concept is misguided. Rotational weight does not affect your handling much more than weight added to the middle of the bike.

Many of the best electric bikes tend to use mid-drive motors as they provide a more natural-feeling option, though they often cost significantly more.

Not only does a torque sensor cost more, and a bottom bracket-mounted motor needs to be more complex, but the frame must be specially designed to house such a motor.

A man rides an electric mountain bike on a green background.

The eBike Frame

Speaking of the frame, this is another integral part of how an electric bike works.

Of course, it serves the same function as for a traditional bike: holding the rider up and connecting all the moving parts, but it also serves additional functions.

The main difference here is that the frame must be specifically designed to house the battery, and, in the case of a mid-drive motor, the motor and sensors as well.

This means that generally the bottom bracket mounting area is significantly larger than that of a mechanical bike, and the downtube will be much wider, too.

Of course, these all need to be connected together, and so wires between the components pass through the tubing.

The frame will often be designed specifically so that the battery and the motor don’t affect the aerodynamics of the bike too much, particularly on performance-focused eBikes.

A cyclist removes the battery from her electric bike.

Now you know how an electric bike works…

This can help you either to understand the best way in which to use your existing electric bike, or perhaps may help you to decide whether an electric bike is for you.

Or maybe it will just spark your interest in these incredible inventions!

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Jack is an experienced cycling writer based in San Diego, California. Though he loves group rides on a road bike, his true passion is backcountry bikepacking trips. His greatest adventure so far has been cycling the length of the Carretera Austral in Chilean Patagonia, and the next bucket-list trip is already in the works. Jack has a collection of vintage steel racing bikes that he rides and painstakingly restores. The jewel in the crown is his Colnago Master X-Light.

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