how ebike engine works

How Does An Electric Bike Engine Work?


Noel Joseph
August 12, 2021

Electric bikes or “e-bikes” have become increasingly popular in today’s continuously evolving society.

These bikes offer the ability for users to ride purely under human power, purely with the electric bike engine, or in many cases with engine assisted pedaling.

This allows riders to decrease physical strain when needed, and travel at higher speeds with less work required. So how exactly do electric bike engines work?

From a fundamental standpoint, electric bike motors function by converting electric energy into mechanical energy, in order to assist with pedaling. They use brushless direct current engines, which perform the conversion of electric energy to mechanical energy.

Conventional electric engines used brushes (mechanical commutators) to control the speed and torque of the motor. However, these brushes rendered their engines less efficient, as the brushes would wear out over time and need to be replaced.

When you take a look inside a brushless direct current motor you will see a circular arrangement of poles with wires wound neatly around each one. This is the stator, which acts as an electromagnet when the engine controller pulls the current from the battery into the wires. There will also be a series of permanent magnets, which are known as the rotor.

Understanding the way that the stator and the rotor interact is essential to grasping exactly how an electric bike engine works. Simply put, currents run through the stator and repel/attract the magnets within the rotor causing it to rotate. The shaft will then spin to generate torque and cause the front or rear wheel to spin, which creates pedaling assistance for the rider.

Types of Electric Bike Engines

There are three main types of electric bike engines, each with their own set of relative pros and cons.

Front Hub Engines

front hub wheel engine

Front hub electric bike engines are always mounted in the hub of the front wheel. These types of engines will pull the rider forward and essentially serve as somewhat of an all-wheel drive system for the e-bike. The front wheel is powered by the engine and the back tire is propelled by the pedals.

Front hub engines are effective on snow, sand and other uneven surfaces thanks to the all-wheel drive style capabilities. They can be used with a normal rear wheel gear & chain set-up because of the fact that the engine is not interfering with the rear wheel or the main drivetrain.

On the downside, front hub engines are usually only available in lower power models because there is less support for a high powered engine around the e-bike’s front fork. They also tend to produce a feeling of being “pulled” along when riding, which can be undesirable for some riders.

Front hub electric bike engines are great for DIY e-bike builds because they do not interfere with the important structural/mechanical aspects of a regular bike. Therefore, they can be fitted to a variety of mechanical bike models without the need for much modification.

However, as mentioned before, the actual riding experience is quite different from that of a conventional bike. If users are looking for high power and speed, front hub engines may struggle to deliver in this area due to the absence of weight over the front wheel.

If you plan to be riding in snowy conditions or on non conventional biking terrain, front hub engines will be able to provide the traction needed to travel safely.

Rear Hub Engines

rear wheel engine

Rear hub electric bike engines are definitely the most common type of engine found in conventional e-bikes on the market. These engines are housed in the hub of the rear wheel, as their name suggests.

Unlike their front hub engine counterpart, these engines provide the push as opposed to the pull feeling that traditional bikers are most familiar with. The engine provides power to the back wheel instead of the front wheel, which means that there will be virtually no chance for any wheel spin.

The fact that rear hub electric bike engines closely resemble the feeling of a mechanical bike means that the new riders will have no trouble adjusting to this style of e-bike. The sensors that are built into these engines are considered to be more intuitive and therefore more responsive to the rider’s movements.

Another important benefit to having a rear hub engine on your e-bike is the wide range of engine power options that are available as opposed to the front hub engine. The support that is already built into a bike frame allows for rear hub electric bike engines to offer more power.

This is often an important deciding factor for riders who are looking for an e-bike that can really fly. In addition, a powerful rear hub engine paired with a proper throttle function will allow the bike to get off of the line quickly.

In terms of the negative aspects associated with rear hub electric bike engines, there are a few obvious downfalls that must be considered. Since the engine and the gear mechanics of the bike will all be in the same location on the bike frame, this can make changing the back tire and making other adjustments a bit of an ordeal.

This positioning will also cause the bike to be quite back heavy, which will make carrying it or transporting it more difficult. However if the battery is mid-mounted, that will help with the overall weight distribution.

Mid-Drive Engines

mid drive engine

Mid-drive engines are affixed directly to the crankshaft which is made up of the pedals and the drivetrain that houses the chain. This type of electric bike engine is actually the least popular at the moment, and although they are becoming more popular, they are usually more expensive.

Due to their location and placement on the e-bike, these engines allow for a lower and more stable center of gravity. This makes them easier to ride in many ways and also easier to carry when the need arises. With a mid-drive engine, removing and performing any adjustments to either the front or back wheel is significantly easier, which gives it an advantage over both front and rear hub engines.

In terms of the feeling of how mid-drive electric bike engines drive/ride, they will be the most natural and similar to that of a conventional bike. These types of motors will tend to have the widest range of travel in comparison to the front hub and rear hub engines. The mid-drive placement of these engines allow the extra weight to be concentrated in the middle of the frame, and therefore will work well with full suspension e-bikes.

There are a few downsides to this style, including heavy wear and tear on the bike’s drivetrain, which implies the need for high quality parts and frequent replacement of these parts. Mid-drive engines come with a number of quirks that need to be understood by riders, including potential gear shifting issues and intricacies.

Which Electric Bike Engine Is Best?

which type to choose

It is somewhat difficult to confidently declare which electric bike engine is best. The problem with answering this question is that another question arises – which engine best suits your needs as a rider?

What kind of e-biking do you plan to be doing? On what style of terrain? How much power are you looking to have available? There are a series of important questions to ask yourself when trying to decide what kind of electrical bike engine will be best for you.

You may be looking for a high top-speed potential, wanting to have a jump off the starting line, or just looking for the raw power to take the work and strain out of your bike rides. In this case, a rear hub or mid-drive engine might be the right choice as opposed to the less powerful front hub engine option.

If power and speed isn’t much of a priority for you as a rider, then a rear hub engine may not be necessary. Maybe you are worried about your bike being back heavy, and plan to be carrying it frequently. In this case a front hub engine may serve you best. Maybe you’re looking for a “pull” type feeling from your electric bike engine, if this is true then a front hub style engine would give you the best experience.

There may be certain aspects of all three engine styles that appeal to your needs. It is crucial to identify which of these are most important for you when making a final decision.

Maybe you have to compromise in certain areas, but ideally you can find an equilibrium that allows you to get exactly what you need from your electric bike engine. Take into consideration everything we have discussed, maybe consult an expert if need be, and choose an engine that will give you the best possible experience.


Noel Joseph

Noel Joseph has been in the world of motor vehicles for a long period. Currently, he is enthusiastic about Electric & Hybrid Motors and is an independent researcher. He advocates for a clean and sustainable future and envisions utilizing his years of experience in mechanical engineering. His new venture here at is to organize and simplify knowledge on Electric vehicles. He wants to build a space where people can talk about EVs and associated technologies with freedom.