A Comprehensive Comparison of E-bike Motors
Electric bikes provide power assistance through an integrated electric motor that supplements the rider's pedaling. There are several types of motors used in electric bikes, each with its own advantages. Understanding the different types of electric bike motors and their characteristics allows riders to select the best motor option to suit their specific riding needs and preferences. In this detailed guide, we will provide an in-depth look at the various types of motors used in electric bikes including hub motors, mid-drive motors, crank drive motors, brushed vs. brushless motors, and friction drive motors.
Table of Contents:
Part 1. How Do E-bike Motors Work?
Part 2. Overview & Comparison of Different E-Bike Motor Types
Part 3. Choosing the Best E-bike Motor
How Do E-Bike Motors Work?
The e motor is the defining component of e-bikes that provide an extra boost while pedaling through electrical assistance. But how exactly do the different types of motors used in electric bikes generate this power assist? Here is an overview of e-bike motor functionality and interaction with other e-bike components:
Interaction with E-Bike Components
On an e-bike, the electric motor works in conjunction with the battery, pedals/crankset, drivetrain, and control system, powered by a rechargeable lithium-ion battery pack. As the rider pedals, sensors detect the rhythm and force from the crankset and bottom bracket, sending this data to the control system, or controller, which in turn activates and modulates electrical assistance from the motor. The electric motor for bicycle then provides mechanical power output that supplements human pedaling power, transmitting power through the drivetrain to propel the e-bike forward.
Role of Sensors
The different types of motors used in electric bikes rely on sensor input to manage power delivery. Most e-bikes with an electric motor have a torque sensor in the crankset or bottom bracket that can measure human pedaling force and cadence in real-time. The controller processes this data along with input from wheel speed and cadence sensors, then activates and modulates electrical power from the battery to the motor in a smooth, seamless way. This sensor-based control allows different types of e-bike motors to provide proportional power assistance in harmony with the rider's own effort, enhancing the riding experience safely and efficiently.
Operating Modes
E-bike engines have different operating modes depending on rider preferences and needs. The most common are paddle assist, throttle assist, and pedal assist.
- Paddle Assist: The electric motor only provides power when the rider is actively pedaling.
- Throttle Assist: It allows the motor to be engaged to propel the e-bike without any pedal input.
- Pedal Assist: Provides power proportional to the rider's cadence and strength, amplifying human input.
Different types of electric bike motor can offer any or all of these modes, which can be controlled by changing settings on the handlebar-mounted display unit.
Power and Efficiency
The controller orchestrates the precise flow of electrical power from the battery to a designated type of e-bike motor, typically measured in watts. While most e-bike motors maintain a continuous power rating between 250-750 watts, their peak outputs can surge beyond 1000 watts. Various types of electric bike engines exhibit efficiencies ranging from 60-90%. A higher efficiency e-motor for bicycle converts a greater portion of battery power into practical mechanical output. Additionally, the thermal design significantly impacts motor performance and longevity. Overall, e-bike motors optimize the balance of power and efficiency.
Overview & Comparison of Different E-Bike Motor Types
There are five main types of motors used in electric bikes, each with their own pros and cons. Selecting the optimum motor type depends on the e-bike design and intended riding style. Here is an overview and comparison of the different types of electric bike motors:
1. Hub Motors
Hub motors are the most widely used type of electric bike motor, estimated to represent 50-70% of the e-bike motor market. As the name implies, hub motors seamlessly integrate into either the front or rear wheel hubs of the bicycle. This kind of electric bike motors are available in geared or gearless variations, and their straightforward, self-contained design eliminates the need for drivetrain modifications. Now let's learn more about the front and rear hub motors!
1) Front Hub Motors
Pros:
- Simpler installation than rear hubs
- Change a flat tire easily
- Do not affect gearing and drivetrain
Cons:
- Add more unsprung weight to the front wheel
- Alter bike weight distribution and center of gravity
- Affect steering and handling at higher speeds
- Require sturdy front fork design
Overall, most electric bike experts recommend against front hub motors except in niche cases, as their steering and stability drawbacks outweigh the easier installation advantage - it may lead to risks such as unstable handling, wheel roll, and reduced front braking power.
2) Rear Hub Motors
Pros:
- Maintain normal bike weight distribution and center of gravity
- Do not affect steering or front suspension
- Preserve predictable handling and stability
Cons:
- Complicated rear wheel removal for flat tire repairs
- Affects the drivetrain, especially with geared hub motors
- Increases unsprung weight, potentially complicating spring shock tuning
Conclusion
Most e-bikes equipped with hub motors opt for a rear hub motor setup to maintain familiar bike handling. Yet, the augmented rear unsprung weight requires adjusted suspension parameters for optimal terrain handling. In essence, rear hubs capitalize on hub motor benefits while minimizing their drawbacks.
Ideal Applications
The self-contained wheel-based design and quiet operation make hub motors ideal for many entry-level e-bikes, especially those simple and affordable e-bikes designed for flat terrain, or recreational urban and commuter e-bikes where high speed is not required, such as Engwe T14.
2. Mid-Drive Motors
Mid-drive motors have become increasingly popular in recent years and now account for approximately 30% of the e-bike motor market. The mid-drive system installs the motor in the bottom bracket area and directly drives the crankset, providing auxiliary power transmitted through the rear gear set and transmission system. This central position optimizes weight distribution while delivering outstanding power and efficiency to maximize traction, acceleration and control.
Pros:
- Optimize bike weight distribution and stability
- Maintain excellent traction even at higher speeds
- Preserve natural riding feel and handling
- Provide great hill climbing capability
- Efficiently utilize gearing to maximize the power band
- Require less battery power for a given performance
Cons:
- Increase system complexity and cost
- Require advanced engineering of crank drive
- Reduce ground clearance around the crankset
- Add weight at the central location on the frame
- More challenging installation and maintenance
Conclusion
Mid-drive motors truly leverage the advantages of an electric bike drivetrain thanks to their central location and integration with bike mechanics. It is recognized and appreciated for providing riders with a natural power transmission and riding experience.
Ideal Applications
Mid-drive motors enable high-performance e-bikes suitable for athletic riding, hills, and competitive use - the central weight localization greatly benefits off-road e-mountain bikes. This electric bike engine is the first choice for electric cargo and electric tandem bikes carrying heavy loads. The superior traction, power band utilization, and hill-climbing make it ideal for premium e-bikes where cost is secondary to performance advantages.
3. Crank Drive Motors
Crank drive motors represent a niche subcategory currently estimated at just 5-10% of the e-bike motor market. This kind of electric motors integrate the motor and gear reduction internally within the crankset bottom bracket spindle. This allows the concentration of weight at the bike's central core while providing weather protection for the motor internals. However, crank drives have limited torque capabilities compared to mid-drive systems.
How Do Crank Drive Motors Work?
Crank-driven e-bike motors cleverly integrate the motor and gear reduction mechanism inside the oversized crankshaft. This unconventional placement is achieved with the help of a specially designed spindle housing. Within the bottom bracket shell, the stator and rotor rotate concentrically, essentially forming the inner housing of the frame. At the same time, the crank drive powers the chain through the rotation of the crankshaft itself and drives the train through integrated gear reduction. This type of motor requires a complex and robust spindle design to handle the internal forces while maintaining pedaling performance.
Pros:
- Concentrate weight centrally at the bike's core
- Improve overall handling stability and performance
- Protect motor internals from weather and debris
- Require no alteration to the rear drive components
- Provide very quiet operation
Cons:
- Integration limits torque and power capabilities
- Significantly increase crankset weight
- Require advanced spindle engineering and design
- Offer less torque capabilities and configuration flexibility compared to mid-drives
- Higher cost due to custom spindle fabrication
Conclusion
While crank drives have some advantages, the limited torque and higher cost make them best suited only for specialty e-bike models at this stage. In addition, crank drive technology remains less mature compared to the more proven mid-drive systems. However, the ongoing advances in spindle materials and design may improve the viability of crank drives over time when incorporated into types of motors used in electric bikes.
4. Brushed vs. Brushless Motors
Electric bike motors use either brushed or brushless motor technology. Brushed motors have been around for decades whereas brushless types are a more recent development.
1) Brushed DC Electric Motors
Brushed DC electric motors have stationary magnets in the stator surrounding a rotating armature that contains wire windings that interact with a fixed magnetic field. To maintain continuous rotation, a mechanical commutator and brushes reverse the polarity of the winding currents. However, over time, the brushes wear down and require periodic replacement.
Pros:
- Simple, low-cost motor construction
- Easy to control speed by varying voltage
- Provide high starting torque
Cons:
- Brushes eventually wear out and need replacing
- Less efficient with more energy loss as heat
- Generate electrical and electromagnetic noise
- Lower power density and peak power capabilities
- Require maintenance due to wearing brushes
Conclusion
Brushed motors represented the early conventional approach used in power tools, appliances, and many electric bikes. However, their disadvantages have led to increased use of brushless electric motors (BLDC/EC).
2) Brushless DC Electric Motors
BLDC, or brushless motor has permanent magnets fixed in the rotor which rotate around a stationary armature. To maintain rotation, complex control electronics sequence power in the windings. Unlike brushed motors, it operates without brushes, as the windings in the stator are electronically commutated.
Pros:
- Eliminate wearing brushes for lower maintenance
- Lighter weight and more compact size
- Higher peak power capabilities
- Improved thermal performance and lifespan
- Higher system efficiency with less energy loss
- Generate minimal noise and electromagnetic interference
Cons:
- Require complex electronic speed controllers
- Produce less torque at low speeds
- Cost more than an equivalent brushed motor
- Sensitive to dirt, dust, and moisture
- Complex troubleshooting and repairs
Conclusion
The popularity of EC/brushless motor continues to increase due to substantial performance, efficiency, and reliability improvements over brushed types. Nearly all higher-end e-bike systems now utilize brushless motor/BLDC motor technology. For example, most popular Engwe bikes use brushless motors, such as E26, M20, EP-2 Pro, etc. In most cases, the disadvantages of added complexity and cost of brushless motors are offset by significant functional advantages, resulting in a better user experience.
3) Sensorless BLDC Motors
Sensorless brushless DC (BLDC) electric motors offer a variant of brushless technology aimed at simpler implementation by eliminating physical sensors. Rather than using Hall Effect sensors or encoders, sensorless brushless engines rely on measurements of voltage and current to provide estimated rotor position for electronic commutation sequencing.
How Do Sensorless Brushless DC Electric Motors Work?
Sensorless BLDC motors estimate rotor angular position based on measurements of current and voltage within the motor windings. By monitoring the back EMF voltage, the associated zero crossings can be used to determine position during normal operation. At standstill and lower speeds, specialized electronic drive methods induce saliency effects that provide position estimation. This sensorless approach eliminates separate Hall sensors or encoders to lower costs, size, and complexity.
Pros:
- Eliminate separate physical sensors and associated wiring
- Enable simpler, more robust, and often smaller motor design
- Reduce overall motor system size, complexity, and cost
- Require no recalibration or realignment of sensors
- Allow operation in harsh conditions with dirt, dust, moisture
Cons:
- May have less smooth startup and low-speed torque control
- Often have lower efficiency at very low motor speeds
- Require complex state estimation algorithms and electronics
- Difficult to provide optimal efficiency across the full-speed range
- Tolerate less parametric variability in motor construction
Conclusion
Sensorless technology works well for many cost-driven applications not requiring the ultimate in precision and smoothness.
5. Friction Drive Motors
Friction drive motors represent a niche class just starting to emerge for electric bikes and other light electric vehicles. As the name denotes, friction drive motors use friction between a rubberized wheel pressed against the tire to propel the bike. This approach results in an extremely simplified design without affecting the bike mechanics. However, friction drive systems also have noticeable drawbacks in performance.
How Do Friction Drive Motors Work?
Friction drive motors attach externally to the bike frame on the rear wheel. A small geared electric motor spins a rubberized wheel that presses against the rear tire. When activated, the friction drive wheel rotates against the tire to propel the bike forward similar to a hand holding a wheel. The motor mounts near the hub and connects to the friction drive wheel by a belt or gear train.
Pros:
- Extremely simple and lightweight external design
- Require no modification to bike drivetrain or wheel hubs
- Quiet motor operation from external mounting
- Easy to retrofit onto standard bikes if desired
- Preserve pedaling friction feel when the motor off
Cons:
- Tend to slip or lose traction, especially on hills or in wet weather
- Limits rear braking capability and performance
- The friction wheel wears over time and requires replacement
- Less robustness and weatherproofing with external exposure
- Lower power and efficiency capabilities overall
Conclusion
Friction drive systems have garnered interest for some low-cost electric bike models, but their performance limitations make them unsuitable for higher-quality e-bikes. Advancing materials science may increase the viability of friction drive motors down the road when incorporated into types of motors used in electric bikes.
Choosing the Best E-bike Motor
Since there is such a wide range of electric bike motors, it can be challenging to select the optimal motor type for your needs and preferences. Here are key factors to consider along with recommendations based on riding style.
1. Key Factors to Consider
- How much assistance do you need - lower or higher power rating?
- What is your typical riding terrain - flats or hills?
- What bike handling traits are most important - stability or agility?
- How much weight can you tolerate adding to the bike?
- What kind of drivetrain are you starting with?
- What level of weatherproofing is required?
- What is your budget for the motor system?
2. Recommendations Based on Riding Style
Let's examine recommendations based on common riding applications:
1) Commuting and Leisure Riding
For casual riding around town or bike paths, a hub motor offers simplicity and cost-effectiveness. Either a geared or gearless rear hub motor provides efficient comfortable power assist without affecting handling. Mid-drives offer higher performance but may be overkill if not utilizing terrain capabilities.
2) Athletic Trail and Mountain Biking
Mid-drive systems shine for off-road riding where their traction, balance, and hill-climbing advantages are essential. Besides, the central weight placement also aids maneuverability on trails. In a word, higher torque mid-drive motors match well the gearing range on MTBs.
3) Cargo Hauling and Heavy Loads
Transporting kids or heavy cargo benefits greatly from the raw power and improved traction of mid-drive motors. Their efficiency and gear utilization provide sustained assistance in lugging extra weight up hills. What's more, dual motored mid-drives can also be spaced for max power cargo bikes.
4) High-Speed Electric Road Biking
To reach higher sustained speeds, mid-drives can leverage road bike gearing better than hub motors. Their dynamic performance also matches well with the agile handling desired at higher speeds. Lower drag and weight aids acceleration and cruising.
5) Budget-Friendly Retrofit Projects
Adding a simple hub motor lets you electrify a standard bike on a budget as a casual cruiser. Rear friction drive systems also allow cheap experimentation with motorizing existing bikes with simplicity and reversibility.
Evaluating your priorities among these key selection criteria allows identify the ideal types of motors used in electric bikes for your individual needs and riding style. In addition to this, test riding different e-bikes, experiencing motor characteristics first hand, combining user experience with technical knowledge can also help to yield the best motor choice. Another point is that you can give priority to some e-bikes equipped with well-known drive motors, such as Bosch ebike motor, Bafang electric motor (e motor), etc.
Final Thoughts
In closing, there are several distinct types of motors used in electric bikes, each with inherent advantages and disadvantages. Broad categories include hub motors, mid-drive motors, crank drives, brushed motors, brushless motors and friction drives. Currently, mid-drive and hub motors dominate the e-bike market. However ongoing innovation across motor types will likely yield shifting popularity and diverging specialization going forward. Consider your riding style preferences and requirements and choose the right e-bike motor for your bike to make your riding adventures fun!
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