Motor lies at the heart of an eBike. It’s what powers your ride and without it, your electric bike is nothing but a simple bicycle. Even though eBikes have been around for years, their working, particularly the working of their motors, still raises many questions. And that’s why we have put together this guide. From discussing how an eBike motor works to the pros and cons of each type, we’ll try to explain everything there’s to know about electric bike motors.
Here are the topics this guide will cover.
- How Do eBike Motors Work?
- Types of eBike Motors: Mid Drive vs Hub Motor
- Types of Hub Motors: Geared vs Direct Drive
- What are Watts, Amps & Newton-Meters?
- Buying Guide: What to Look For?
- eBike Motor Kits
How Do eBike Motors Work?
The motor can be considered the engine of an eBike. Just like an engine uses gasoline to move a vehicle, it uses the electric power generated by the battery to propel an electric bike. So, the main role of an eBike motor is to convert electrical energy into mechanical energy needed to rotate the wheels.
There are many types of electric motors out there, but brushless DC motors (or BLDC motors) have become an industry standard for eBikes. Before we dig deep into how does an eBike motor work, let’s first discuss the parts of a brushless eBike motor.
Brushless DC motors have two main parts: a rotor and a stator. As the names suggest, the rotor is the part that rotates while the stator is what remains stationary throughout the working of the motor.
The rotor of a BLDC motor has a circular series of permanent magnets. The stator, on the other hand, has a coil arrangement around a circular series of poles. Unlike the rotor, the stator is an electromagnet, which means it becomes a magnet only when current passes through its wires.
A brushless eBike motor works/ rotates due to the interaction between the magnetic fields of the rotor (the permanent magnet) and the stator (the electromagnet). When the current passes through a coil at the start of the rotation cycle, it becomes an electromagnet and attracts the rotor’s permanent magnet towards itself.
As the rotor moves towards the coil, the next coil in the sequence is energized and the process is repeated for all subsequent coils to keep the rotor moving/ rotating.
It’s just like the humorous analogy of the donkey and the carrot, where the donkey tries to reach the carrot but it keeps moving with it.
To further increase the efficiency and power output of the motor, when the rotor moves towards a certain coil, the coils behind it are energized with opposite polarity so that they repel it and produce more torque (aka the rotation effect).
A Hall effect sensor ensures seamless rotation by determining which coils to energize at a certain point in time.
The torque produced by the motor is then shifted to wheels, though the exact mechanism may differ with respect to the placement of the motor as well as the presence or absence of gears in it.
What you just read is how a direct drive (gearless) hub motor, the simplest of all eBike motors, works. In the direct drive hub motors, the motor shaft doesn’t spin (as it forms the axle) and the rotor directly spins either the front or rear wheel.
The geared hub motors operate just like the direct drive ones, except for one main difference. They have a series of planetary gears to lower the motor RPM and increase the torque output. In mid drive motors, which are almost always geared, the shaft is connected to a small chainring to give pedal assistance to the users.
Brushless DC motors can either be inrunner or outrunner, depending on whether the rotor rotates ‘inside’ the stator or ‘outside’ of it.
Why Do eBikes Use Brushless Motors?
Brushless DC motors have a lot of advantages over the brushed motors found in older electric motors.
The brushed motors use brushes and commutators to alternate the direction of the current, which wear down over time due to continuous contact. Being free of these troublesome components, the BLDC motors are practically zero-maintenance when compared to the brushed ones.
Besides their high durability, the BLDC motors also don’t produce sparks and electrical noise like that of the brushed motors. The biggest advantage of brushless eBike motors, however, is their stellar power efficiency. For a similar torque output, a BLDC motor is considerable smaller than the brushed one and can rotate at a high speed under any condition.
Another significant advantage is that BLDC motors can be easily controlled to precisely deliver any amount of torque or rotation speed, which in the case of eBikes means full control over the ride. This precision in control, combined with the absence of friction, reduces heat generation and energy consumption to eventually increase the battery life.
To sum it up, brushless eBike motors are powerful, compact, lightweight, silent, reliable, durable, and low-maintenance.
How eBike Motor Works With Rest of the Bike?
An eBike motor works with batteries and controllers to complete the power troika of an electric bike. The battery is the source of electric current that flows into the motor and controllers are what regulate this process.
Controllers basically take input from the user and allow the desired amount of current to flow from the battery into the motor. If the controller draws more current from the battery, you’ll experience more power (pedal-assist), faster speed, and better acceleration.
But how does the ebike controller work? How do they know your power requirements? Well, they do this by sensing either your pedal speed or pedal strength.
A speed or cadence sensor regulates the amount of power (pedal-assist) you get by detecting your pedaling cadence or, in simple terms, how fast you pedal. While a torque sensor does so by detecting how much torque you’re putting into the pedals or, in simple terms, how hard you pedal.
If you want to explore more about how these two types of sensors differ from each other, check out this in-depth torque vs cadence comparison.
Most eBikes also have a throttle mode, which allows riders to use the motor power without any pedaling at all.
The throttle mode is kind of a rudimentary system and is the only power delivery mechanism in eScooters. It delivers power in accordance with how much you twist the throttle (in the case of eScooters) or push the lever (in the case of eBikes).
Types of eBike Motors: Mid Drive vs Hub Motor
There are no specific types of eBike motors and we can classify them in as many ways as we want. However, we’d stick to the eBike motor types vis-à-vis their placement in the bicycle frame.
So, when it comes to motor placement, there are two main types of eBike motors: mid drive and hub drive. Let’s see how these eBike motors work, what pros and cons they have, and how they differ from each other.
How Does a Mid Drive eBike Motor Work?
Located within the center of the frame midway between the bike cranks around the bottom bracket, a mid drive motor applies a direct force on the mechanical drivetrain comprising of either a traditional chain (along with a cassette and chain rings) or a belt to drive the rear wheel and propel the electric bike.
Pros of Mid Drive Motor
Being directly connected to the drivetrain and, by extension, your pedaling inputs, mid drive motors boost the pedaling force to give natural and highly responsive pedal assistance which makes them suitable for numerous types of riding.
These motors can also deliver more peak power than their hub counterparts and are, therefore, perfectly suitable for electric bikes designed to offer higher levels of assistance, such as electric mountain bikes (eMTBs).
Mid drive motors place most of the weight at a low position, which keeps the center of gravity at an optimum position. For a similar power hub drive motor, a mid drive motor would produce more torque and would distribute weight more evenly. To top it all, they are considerably more efficient than hub motors and allow for extended mileage.
Cons of Mid Drive Motor
As a downside, mid drive motors are more expensive than hub motors, mostly because of their peculiar placement. Being located inside the eBike frame, they need a frame that’s designed around them.
Mid drive motors are also more powerful, which isn’t a negative thing in itself but becomes so when you have to complement them with a bigger battery. The biggest disadvantage of a mid drive motor, however, is the increased drivetrain wear that translates to a higher maintenance cost.
Check out our top picks for eBikes with mid drive motors:
How Does an eBike Hub Motor Work?
Hub eBike motors are much simpler than their mid drive counterparts.
Placed inside the hub of the wheel, the shaft of a hub motor doesn’t spin, as it forms the axle of the wheel. Instead, it’s the motor and, by extension, the hub that spins either the front or the rear wheel, depending on where the motor is installed.
Pros of Hub Motor
Hub motors are affordable and highly versatile. They are extremely easy to maintain since they directly deliver motor power to the hub of the wheels and don’t need a chain to operate the eBike.
These motors are usually smaller and lighter as they need to fit inside the hub of the wheels, and are paired with lighter batteries, all of which makes for a compact and lightweight electric bike. Hub motors are suitable for urban dwellers and other riders who don’t want crazy performance from their eBikes.
Some eBikes feature dual hub motors, one on each hub, to form an all-wheel drive that works well on snowy, muddy, and sandy terrains, and is also suitable for off-roading.
Cons of Hub Motor
Single hub motors have an uneven front-to-back weight distribution which doesn’t significantly impact the ride handling on the tarmac. But once you’re off the road, this uneven weight distribution can pose a serious challenge.
Front hub motors usually have problems with traction, especially when cornering at accelerating speeds or going uphill. Rear hub motors, on the other hand, make things messy whenever you need to change the rear tire.
Check out our top picks for eBikes with hub motors:
If you want to explore more on how the hub and mid drive motors differ from each other, check out this in-depth hub vs mid comparison.
Types of Hub Motors: Geared vs Direct Drive
When it comes to the way power gets from the motor to the wheels, there are two types of eBike motors: direct drive hub motors (also known as gearless hub motors) and geared hub motors.
Direct drive and geared hub motors can also be considered as the types of hub motors, as almost all mid drive motors are geared in nature. Let’s see how these two kinds of hub motors work, what pros and cons they have, and how they differ from each other.
How Does a Direct Drive (Gearless) Hub Motor Work?
The working of direct drive (gearless) hub motors has already been explained in detail above (the shaft forms the axle, and the motor aka the hub rotates around the shaft; you probably know it by now).
The key thing to note here is that a direct drive hub motor has no gears or any other kind of moving parts in it. It’s just the motor that rotates around the axle, and that’s it.
Pros of Direct Drive Hub Motor
Direct drive hub motors have fewer moving parts than their geared hub counterparts and, therefore, require less maintenance. The absence of gears also means that there will be no gear noise.
Since the direct drive hub motors spin at the same speed as the wheels, they are suitable for high-speed eBikes, such as the Class-3 electric bikes that can legally move at up to 45km/h (28mph).
However, this increase in speed comes at its own price, which we’ll discuss shortly.
The direct drive hub motors offer the possibility of regenerative braking, thanks to their perfectly bidirectional nature. When the brakes are applied, a cutoff switch allows the motor to act as a generator which uses the resistance to generate electrical energy that goes back into the battery.
While it may sound amazing, the actual amount of regenerated energy is disappointing because let’s face it, an eBike is no electric train!
Though it may do little to increase your battery life, regenerative braking can still help you a lot, particularly if you use a cargo or any other heavy eBike on long descents.
The main advantage is that the braking energy gets absorbed electronically instead of by friction, which means you don’t have to constantly apply the brake while going downhill. It saves your brakes from overheating and your brake pads from wearing out.
Cons of Direct Drive Hub Motor
Direct drive hub motors inherently lack torque due to their gearless design and are, therefore, not good at climbing hills. To overcome this shortcoming, they use bigger magnets, which makes them large and heavy. They usually have a dia over 8” (20cm) and may weigh up to 20lbs (9kg).
Being larger and heavier, these motors consume more battery power and deliver low mileage when compared to geared motors. Also, since the direct drive hub motors spin at the same speed as the wheels, it translates to a lower motor RPM which drastically limits the motor efficiency at low speeds.
The direct drive hub motors also lack freewheel, which means they would be harder to pedal without the electric assist in case your battery dies on the road. Lastly, they cost more than the geared hub motors, especially the ones with regenerative braking.
How Does a Geared Hub Motor Work?
The working principle of a geared hub motor is similar to a direct drive one. However, unlike a gearless motor, it rotates at a much higher rate while inside the hub, and its shaft is connected to the hub via a series of planetary gears that lower the motor RPM and spin the hub at a lower speed, but with a considerably larger torque output.
Pros of Geared Hub Motor
Though the planetary gears make the hubs wider, geared hub motors are considerably smaller and lighter than their gearless (direct drive) counterparts for similar torque ratings. They weigh less than 9lbs (4kg) and are getting lighter every year.
Since the geared hub motors can produce a greater torque output, they’re perfect for hill climbing and other high-torque uses. Being relatively low-speed, they’re suitable for Class-1 and Class-2 eBikes that restrict top speed to 20mph.
Moreover, thanks to their freewheel, they are easier to pedal in the absence of electric assistance as they move freely just like any traditional bicycle. Last but not least, the geared hub motors cost less than the gearless systems.
Cons of Geared Hub Motor
Having more moving parts translate to more wear and, eventually, more maintenance costs. The geared hub motors are, therefore, relatively less durable in long term than their gearless counterparts, particularly when they regularly move heavy loads up steep hills.
The presence of gears also means that these motors will not be as silent as the gearless (direct drive) hub motors, though some manufacturers have managed to churn up some amazingly quiet units. And don’t forget that the freewheel always comes at the cost of regenerative braking.
What are Watts, Amps & Newton-Meters?
The power ratings of an eBike motor can be extremely confusing, but in order to make the right buying decision, it’s crucial for you to know them. Here is a comprehensive breakdown of three of the most important power metrics related to electric bike motors.
Watt is, scientifically speaking, a measure of power, but in the case of eBike motors, it isn’t always the best representation of their power output.
Most of the time, you’ll see eBike manufacturers listing the nominal and peak output of a motor, both of which are measured in Watts. Some companies publish only peak power ratings, which can be a bit misleading.
Nominal power rating refers to the amount of power that a motor can continuously produce without overheating or damaging itself. It’s basically what the motor has been designed for. Peak power rating, on the other hand, is the maximum power that a motor can produce for a short period of time.
While some eBikes can operate at their peak power rating for an extended period of time, most can sustain their peak output for just a few seconds. As the eBike industry is just getting started, there are no universal standards for peak power duration and no independent testing sources for this kind of data.
Short for ampere, amp is the rate at which current passes through a point and is used to designate the regulating capacity of the motor controller. In simple words, it shows how much current the controller pulls from the battery and pushes into the motor.
Though amps reflect the amount of current the motor controller can regulate, they can better indicate the motor power than the arbitrary power ratings listed by the manufacturers. You can find out the actual output of a motor by multiplying the voltage of the battery with the amps of the motor controller.
For instance, if a battery is rated at 24 volts and the controller can regulate 12 amps of current, the motor will have a power output of 288 watts (24V x 12A = 288W). But you’ll not get 288 watts because no motor is 100% efficient. The actual power output you get will depend on the efficiency of your motor. For instance, if it’s 80% efficient, the power output will be 230 watts.
Also, amps of a motor regulator should not be confused with amp-hours (Ah), which is basically a measure of battery life and, by extension, the mileage of the electric bike.
If you want to know how powerful an eBike motor is, the best way is to check out its Newton-Meters (Nm). Newton Meters measure torque or the turning force of the motor which is less subjective and, therefore, the most accurate representation of motor power.
Torque is what helps you accelerate, get up a hill, start out while carrying a heavy load, or tackle challenging terrains. Since it’s these troubling times you need the most help from your eBike, checking out the torque rating of an eBike motor can help you make the right buying decision.
Buying Guide: What to Look For?
Now that you know the fundamentals of electric bike motors as well as their power ratings, let’s now briefly discuss the various factors you need to consider for selecting the right eBike motor for yourself.
Size & Weight
Most eBike motors weigh around 3-4kg (6-9lb), though some may be a bit lighter, or heavier. Likewise, the size of the motors varies a lot. The size and weight of an eBike motor may influence the aesthetics, geometry, and portability of an electric bike, but they have little impact on the motor performance.
We don’t mean that they have no impact on how an electric bike motor works, it’s just that they’re much less important than other factors, such as the torque rating or motor placement in the frame.
Usually hovering around 40Nm for road eBikes to 85Nm for electric mountain bikes (eMTBs), torque rating is the single, most important thing to look for in an eBike motor. As we explained above, torque is what helps an eBike tackle all challenges of the ride, so it’s crucial to buy a motor whose torque output is in accordance with your use case.
Also, it must be kept in mind that torque rating is independent of the nominal power output of an electric bike motor. For instance, a 250W Mahle Ebikemotion rear motor has a torque of 40Nm, while Fazua offers a torque output of 60Nm for the same wattage and weight.
Front hub motors are affordable but they have severe traction problems and are kind of outdated. Rear hub motors, the next best option, are suitable for road use. Dual hub motors offer all-wheel drive, which not only enables off-roading but also allows for usage on sand, mud, and snow. Mid drive motors are the most premium option and are perfect for both off-roading and climbing long ascents.
Geared or Gearless
Geared hub motors are lighter, easier to pedal if the battery dies, and perform great on hills due to greater torque output. However, they’re noisy, low-speed, and high maintenance.
Gearless (direct drive) hub motors can allow for more speed and are suitable for Class-3 electric bikes. They also offer regenerative braking that might be helpful for cargo or other heavy eBikes on long descents. But they’re heavier, expensive, bad on hills, and harder to pedal in the absence of electric assist.
Controller & Battery
If you plan to use your electric bike for high-torque uses, make sure to go for a controller that has more regulating capacity or, in simple words, more amps. Likewise, to sustain the power output, you’ll be needing a bigger battery, the one with more amp-hours (Ah).
Levels of Assist
Most electric bikes offer multiple riding modes ranging from manpower to pedal-assist to pure electric (throttle). The riders can further adjust their pedal-assist at different levels to get precise control over their ride. As a general rule, the more levels of assistance an electric bike offers, the more control you’ll have over the power output of the motor.
Type of Sensor
A speed or cadence sensor regulates your motor output and, by extension, the pedal-assist depending on how fast you pedal. Usually found in eBikes with hub motors, these sensors are affordable and low-maintenance. However, they’re not so responsive, feel unnatural, and can produce unpredictable results at times.
A torque sensor controls the power output of a motor by detecting how hard you pedal or how much torque you put into the pedals. Using an electric bike with a torque sensor is just like riding a traditional bicycle. Often found on mid drive eBikes, especially eMTBs, these sensors produce predictable results and give riders complete control over the electric assist.
You must always consider your state laws and local regulations regarding electric bike motors when making your buying decision.
In Europe, Australia, and the UK, eBike motors can only deliver up to 250 watts of continuous power output and cannot assist riders over 25km/h (15.5mph). In the US and Canada, the power output limitation varies from state to state, with most allowing 750W (1hp) of max power.
As far as the speed and levels of assistance are concerned, a Class-1 eBike can only have pedal-assist and a maximum assisted speed of 32km/h (20mph). A Class-2 eBike also tops out at 32km/h (20mph) but it can have a throttle. A Class-3 eBike again has just pedal-assist, but a maximum assisted speed of 45km/h (28mph).
eBike Motor Kits
If you have a thing for DIY, you can retrofit any traditional bicycle with an eBike motor kit to convert it into an electric bike.
For instance, Swytch Universal eBike Conversion Kit is one of the lightest eBike motor kits on the market, with a total weight of just 3kg (6.5lbs). It features a 40Nm brushless motor good for a top speed of 32km/h (25mph) and a compact and fast-charging Lithium battery good for 50km (31mi) of range.
Available in both hub and mid drive systems, eBike motor kits cost less than a new electric bike but they often give a messy look to your ride. Here are our top picks for the best eBike motor kits on Amazon:
If you want to explore more options, these are the best electric bike conversion kits on the market today.
If you don’t want to buy a complete aftermarket motor kit, you can separately purchase a motor, battery, and pedal-assist system to build a fully customized electric bike that best suits your needs, but that would require more technical expertise.
Can I ride my eBike without battery power?
Yes, you can ride your eBike without battery power. However, keep in mind that the electric bikes that use gearless/ direct drive hub motors are harder to pedal in the absence of electric assist than the ones that use geared hub motors due to the absence of freewheel.
How many watts do I need?
Watts, as we explained above, isn’t always the best measure of motor power. Torque rating, which is measured in Newton-meters (Nm), provides a much more accurate insight into the power of an eBike motor. For instance, a 250W motor can be more powerful than a 350W motor if it has more torque rating.
What are the best eBike motor brands?
Bosch, Shimano, Yamaha, and Brose are undisputedly the best eBike motor brands on the market today. Their motors are extremely sophisticated and insanely reliable. These brands constantly keep developing their products, so you can’t really go wrong with them.
Are eBike motors interchangeable?
There’s no straightforward answer to this question. While you can swap a motor for another in some rare cases, most of the time, you need to change almost all of the related components. So, eBike motors are not easily interchangeable.
Are eBike motors waterproof?
Electric bike motors, like other eBike components, are water-resistant which is technically different from being waterproof. It means eBike motors can bear water splashes but not full submersion in water. Also, the amount of water an electric bike motor can withstand greatly differs between models.