How Electric Bike Engine Works [Complete Guide]

A lot of tech wizardry makes electric bikes in California possible. What sets ebikes apart from others is that Li-ion batteries power their engine.

The motor is used to assist with the movement of pedals. This makes it less taxing to ride ebikes. These electric bikes have become less expensive and more widespread. Their total range also increases by several miles (to 100 miles). Here are the details.

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A Small Confusion

Some people confuse electric bikes with conventional motorcycles. Electric motors and their batteries don’t last as long as gas-powered engines.

Electric bikes in California don’t have the same range as motorcycles. But what they lack in range, more than make up for in environmental friendliness.

Electric bikes are a better option for the planet because they don’t generate exhaust. GHG emissions go down the use of e-bikes.

Ebikes are a better option for motorists. It’s ideal from a fitness point of view and improves cardiovascular health.

Unpacking the Electric Bike Engine

It is important to note that engines run on combustion. Electric bikes run on electricity; therefore, they are technically motors. The two words are often used interchangeably.

In either case, here’s how the engine, or motor, works.

All electric motors convert electrical energy to mechanical energy. Force is greeted within motors due to the interaction between the magnetic field and current.

The engine rotates the shaft by periodically swapping the polarity of the electromagnetic. This converts electricity into torque and turns the wheels.

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Some ebikes also make use of regenerative braking. In this case, the electromagnetic forces convert the motion back into electricity.

Increasing the current output will increase the strength of the magnetic field. Voltage may have to be increased to maintain the same current flow.

Ebikes often use brushless DC motors.

These motors do not use brushes to change current flow to the engine. Brush DC motors used to be the norm, but they were less efficient.

Brushes also tend to wear out over time. This is why brushed DC motors were eventually phased out, and brushless motors became standard.

The advantage of brushless motors is a longer life span, high efficiency, and low maintenance. Brushless motors cost more and require complicated speed controllers.

A Look Under the Ebike Engine

You’ll have to navigate a maze of wires and various poles. What you’re looking at is a stator that is often connected to a shaft.

Its feature is that it works like an electromagnet when exposed to current. Electric bikes use permanent magnets arranged in a circular series called a rotor.

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They are attached inside or outside the stator. The exact arrangement of the magnets depends on the electric bike.

The rotor and the stator are essential for understanding how ebike engines work. When electric current flows through the electromagnets, it repels and attracts magnets.

Mid-drive motors spin the shaft to build up torque. This torque is where all the pedaling assistance comes from.

Hub motors use the shaft as an axle; this means they do not spin. Instead, hub motors spin the rotor itself.

This causes the entire motor hub to move and generate torque to spin the wheel.

Read Why Is My Electric Bike Not Working?

Types of Electric Bike Engines

Mid-Drive Engines

Mid-drive motors are located in the crank of electric bikes. As explained earlier, the mid-drive motor generates torque to spin the shaft. This moves the wheels.

Mid-drive motors also feature gear reducers. This system of gears allows riders to tweak the speed and torque.

Mid-drive motors can spin hundreds of times per minute. This is faster than any human can keep up with.

The gear reducer lowers the RPMs and makes the ebike rider-friendly. Most gear reducers keep the RPM between 60 to 80.

Nearly all mid-drive ebikes include gear sensors that cut power to the motor. There is a high risk of breaking the change when the ebike isn’t in gear.

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In general, mid-drives are more efficient than hub engines. They leverage the existing geared drivetrain for low-speed climbing.

Furthermore, their positioning at the center of the ebike provides a balanced ride. This allows mid-drive engines to be used in mountain ebikes.        

It is easier to change tires on mid-drive ebikes. This is because there is no wiring within the wheelset, unlike hub engines.

The disadvantage is that mid-drive motors can increase wear and tear on ebike engines. Make sure only to buy ebikes from reputed manufacturers.

Some manufacturers are known for skimping out on chain quality. Mid-drives are more expensive.

This is because they feature more mechanical components and higher gear reduction. This comes at a higher cost.

Direct Drive Hub Engines

Direct drive hub ebike motors are relatively simple to understand. The shaft acts as the rear axle. This is because it is placed in a fixed spot.

The motor spins the shaft, allowing you to move the ebike. Direct drive hub motors tend to be larger than geared hub motors.

Bigger hubs often result in higher torque outputs. This is needed to lower the RPMs adequately.

Direct drive motors may also utilize regenerative braking to recharge batteries. Since they are bidirectional, they can efficiently go forward and backward.

Pressing the brakes allows the motor controller to turn into a generator. The ebike’s resistance to braking creates energy.

Note that the energy gained from regenerative braking is minimal at best. It is more noticeable in larger objects like electric bikes. But ebikes are too small to generate enough power.

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Energy gains from regenerative braking are much higher in uphill areas. The main benefit of regenerative braking is the stopping power.

This is because the braking energy is absorbed electronically instead of through friction.

Geared Hub Engines

Geared hub motors share many similarities with direct drive hub motors. The difference is that electric motors in hubs spin at a very high speed.

The shaft in the motor is connected to several planetary gears. These gears are connected to the hub, allowing it to spin at a lower speed.

This creates more torque at the risk of lower top-end speed. Geared hub motors have a small diameter compared to direct drive motors.

This is by choice, though. Geared hub motors do not need to be large to create torque. However, the use of planetary gears makes the hubs wider.

These motors also come with a freewheel, which eliminates regenerative braking. Instead, the motors will freely coast and act like regular bicycles when not under power.

Read Which Electric Bike Has the Longest Range?

Components of an Electric Bike Engine

All electric bikes in California have batteries and motor controllers. These fundamental components are the building blocks of electric bikes.


Every electric bike is outfitted with a battery pack – otherwise, it won’t be an ebike! The battery pack is one of the most expensive parts of the ebike.

In their earliest days, ebikes used lead acid, NIMH, and nickel-cadmium batteries. However, manufacturers now prefer to use lithium-ion batteries.

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This technology is more mature and allows manufacturers to create batteries with a high capacity. Lithium-ion batteries are compact and feature hundreds of cells.

As a result, their capacity is very high despite being relatively lightweight. And the technology has improved considerably in recent years, reducing the weight even more.

Lithium battery packs are made using smaller lithium cells in a battery module. Lithium cells come in many shapes and sizes, but the cylindrical format is popular.

The formats 18650 and 21700 are widely used to make lithium battery packs. The cells are manufactured by brands like Samsung, LG, Sony, and Panasonic.

Cylindrical cells are safer and more reliable than other cells. Electric bikes in California also feature a battery management system (BMS).

The BMS tracks the voltage on each cell and prevents them from being overcharged. The number of cells in the battery and their arrangement determines the capacity and voltage.

Most ebike batteries have a voltage of between 36V and 48V. You will also see battery packs as high as 72V.

Lower voltage battery systems require heavier gauge wires and connectors to draw more current.

Higher voltage systems have a high electrocution risk. This is why manufacturers keep battery packs within the 36V to 52V range.

The amperage is low enough to use cheaper wiring and connectors. Moreover, the risk of electric shock is very low for riders.

The capacity of electric bikes is expressed in watt-hours. Some manufacturers may also use amp-hours. Note that watt-hours is simply the voltage multiplied by the amp-hours.

Watt-hours determine the total energy stored in the battery pack. It directly affects how far the electric bike in California will travel.

Most battery packs are rated from 200 watt-hours to 1000 watt-hours. Increasing the capacity would come at the risk of making the ebike too heavy.

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Most manufacturers place the battery into the ebike’s frame tubing. This cleans up the exterior and looks great.

The only problem with this arrangement is that it makes it difficult to replace batteries. This is bad news for owners of ebikes that have been discontinued.

The Controller

As the name suggests, the controllers regulate power from the batteries to the motors. Riders can tweak the power using the controller based on their requirements.

In essence, the controller determines how fast your wheels spin. This can get slightly more complicated for ebikes depending on the level of assistance offered.

The controller serves two essential functions:

  1. Converting DC voltage from the battery pack into 3-phase AC. Without this current, the motor would not spin.
  2. Continuously adjusting the voltage to the motor, from 0V to full voltage. The controller adjusts voltage in response to the cyclist’s throttle signals and pedal sensors.

The controller can reduce the voltage to any value between 0V and battery voltage. A 48-voltage battery pack may only provide 10 to 12 volts at low speeds.

This table shows how voltage is adjusted based on ebike speeds (for 48V battery packs)

SpeedVoltage (V)
Low10 to 12
Moderate25V or higher
Top-end speeds48

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You might see various options on the controller depending on the type of ebike. There is the ‘pedal-only mode’ if you want to ride without any assistance.

Pedal-only mode is where the motor receives zero power from the battery. The rider does all the work to move the electric bike.

But what if you come across a steep uphill and need some assistance? This is where the motor comes in handy.

You can now switch to ‘pedal assist mode’. This is where the motor and you work together. Engines are also strong enough to do all the work without requiring input from cyclists.

You can activate ‘electric-mode only’ if you are completely tired. This means you can take your feet off the pedals. The motor will move automatically – just like a regular motorcycle.

You still have to maintain your balance, of course! You can change the settings using a small device mounted on the handlebar.

This device tweaks the controller to help you choose how much power is drawn. The device comes with a display and information about your ride.

It lets you see how much charge is left and how much range is covered. Some devices also track calories burnt, power used, and speed.

Torque Sensors

Torque sensors allow the bike to be controlled from the pedaling sensors. These sensors are installed on the existing crankset.

They send signals to the ebike when you spin the pedals. Torque sensors sense when you pedal the ebike and how hard you push the cranks.

How Electric Bike Engine Works
How Electric Bike Engine Works

Wrapping Up

So there you have it, a quick look at how electric bike engines work. The basic concept for all ebike engines are the same.

They use the interaction between magnetic fields and current to facilitate motion. How they go about accomplishing this phenomenon is where the differences set in.

In general, mid-drive motors are more popular among cyclists. Let us know if this article explained the concept to you.

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