E-Bike Torque and Power: No Confusions Ever Again

In the realm of electric bicycles, the concepts of power and torque often seem to cause confusion among potential buyers. This blog post aims to shed light on the distinction between these two crucial performance metrics and empower you to make an informed decision when selecting an electric bike that aligns with your specific needs.

What Determines the E-Bike Power?

The power of an e-bike is primarily determined by the design and specifications of its motor. Power is the rate at which work is done, and it is typically measured in watts (W). The power of an electric bike affects its top speed, acceleration, and hill-climbing ability.

The power of an e-bike can be calculated using the following formula:

P(kW) = (T(Nm) * n(rpm)) / 9549

where torque is the rotational force produced by the motor and RPM is the rotational speed of the motor. Electric bike motors are typically designed to provide enough power to meet the needs of everyday commuting and recreational riding, while also considering battery range.

In addition to the motor, the power of an e-bike is also affected by the following factors:

• Battery voltage: The higher the battery voltage, the more power it can provide.
• Controller: The controller manages the flow of current, which affects power output and acceleration performance.
• Bike weight: Bike weight affects power demand, as a heavier bike requires more power to maintain the same speed.

Rated Power versus Maximum Power

The maximum power of an e-bike motor is not a fixed value. The motor’s power can vary within a certain range, depending on the motor’s design and operating conditions. The motor’s rated power is the power that the motor can continuously output under normal operating conditions, while the maximum power is typically the highest power output that the motor can achieve for a short period of time.

In real-world use, an e-bike’s motor may temporarily exceed its rated power when faced with demanding riding conditions, such as uphill climbs, acceleration, or carrying heavy loads. For example, the motor may have an overload capacity that allows it to provide more power than its rated power for a short period of time to handle specific riding demands. 

Additionally, the controller of an e-bike also affects the motor’s power output. The controller can adjust the current supplied to the motor, thereby controlling power output and acceleration performance. For instance, many electric bikes with 750W have a 48V 20A controller, when the controller fires it all off, it will output 48V*20A=960W to the motor, and seldom the motor will burn because it has overload capability. Therefore, the maximum power output of the motor is also limited by the controller settings and battery voltage.

Overall, the maximum power of an e-bike motor is not a fixed value but rather can be adjusted based on the motor’s design, controller configuration, and operating conditions. This flexibility allows e-bikes to maintain good performance and efficiency in different riding environments.

The Real Differences Between E-Bike Brushless DC Motors of Different Power Levels

When it comes to brushless DC motors, power isn’t everything. While higher wattage motors generally offer more power and torque, they also come with increased size, weight, and cost. So, what exactly differentiates brushless DC motors with varying power ratings, such as 250W, 500W, 750W, and 2000W? Let’s delve into the key distinctions that set these motors apart.

1. Stator Windings

The stator windings, composed of enamel-coated wires embedded in the stator core, are responsible for generating the motor’s magnetic field. Several factors within these windings influence the motor’s power output:

• Number of Turns: Higher-power motors boast a greater number of turns in their stator windings. More turns translate to stronger electromagnetic forces, leading to increased power.
• Wire Cross-Sectional Area: The cross-sectional area of the wires in the stator windings also plays a crucial role. A larger cross-sectional area allows for higher current flow, enabling the motor to deliver more power.

2. Permanent Magnets

Permanent magnets, another key component in generating magnetic fields, contribute significantly to motor power. Their characteristics influence the overall power output:

• Volume: Larger permanent magnets are found in higher-power motors. This increased volume translates to a stronger magnetic torque, boosting the motor’s power.
• Material: Higher-power motors typically employ permanent magnets made from materials with superior magnetic properties, such as neodymium iron boron (NdFeB). Stronger magnetism leads to enhanced magnetic torque and power output.

3. Lamination

The lamination, also known as the stator core, serves as a conduit for magnetic flux and minimizes stray magnetic fields. Its properties impact motor power:

• Size: Larger laminations are used in higher-power motors. This increased size allows for more magnetic flux lines to pass through, enhancing power output.
• Material: Higher-power motors often utilize lamination materials with higher magnetic permeability, such as silicon steel sheets. Improved permeability strengthens the lamination’s ability to guide magnetic flux, contributing to greater power.

4. Air Gap

The air gap, the space between the stator and rotor, influences the coupling of the magnetic field between them, affecting motor power:

• Size: Higher-power motors feature a smaller air gap. A reduced air gap enhances the magnetic field coupling, resulting in increased power output.

5. Cooling System

During operation, motors generate heat, and efficient heat dissipation is crucial for maintaining performance. Higher-power motors require more effective cooling methods:

• Cooling Type: Higher-power motors typically necessitate more efficient cooling mechanisms, such as forced air cooling or water cooling. These methods enable the motor to operate at higher power levels without overheating.

6. Other Components

Apart from the aforementioned factors, other components also contribute to the power differences between motors:

• Bearings: Higher-power motors require heavier-duty bearings to withstand the increased torque and speed.
• Housing: Higher-power motors demand more robust housings to handle the greater mechanical stresses.

Summary

In essence, the power distinctions between brushless DC motors of varying ratings stem from the deliberate modifications made to their internal components. Higher-power motors feature larger, higher-quality components designed to handle higher currents, generate stronger magnetic fields, and deliver greater torque. The table below summarizes the typical internal structural variations across different power levels:

It’s important to note that these are general trends, and specific implementations may vary.

What Gives an Electric Bike Motor Overload Capability?

An electric bike motor’s overload capability is its ability to withstand more than its rated power for a short period of time. This capability allows the motor to handle temporary high-load demands without damaging its performance. The overload capability of an electric motor is typically determined by several factors:

• Motor design: The physical construction of the motor, such as the design of its windings, magnetic materials, and cooling system, all affect its overload capability. A well-designed motor can withstand loads above its rated power for a short period of time without overheating.
• Thermal capacity: The thermal capacity of the motor determines how much heat it can store when overloaded. A motor with a larger thermal capacity can absorb more heat, allowing it to operate during overload without damage.
• Insulation rating: The insulation rating of the motor windings indicates their ability to withstand overload. A higher insulation rating means the windings are less likely to overheat and damage due to overload.
• Cooling system: An effective cooling system helps dissipate heat from the motor during overload, preventing it from overheating. This may include fan cooling, liquid cooling, or other heat dissipation mechanisms.

The overload capability of a motor is part of its design, ensuring it can handle sudden high-load situations, such as the extra power needed for starting, accelerating, or climbing hills, for a short period of time. However, prolonged overload operation can damage the motor, so it should not be continuously operated in an overloaded state.

Note that overload capability does not mean the motor can run indefinitely at a power level above its rated power. Overloads are typically temporally, and the motor is designed to handle them without compromising its lifespan. Electric bike use and maintenance should follow the manufacturer’s guidelines to ensure safety and efficiency.

Significance of E-Bike Motor Power in Real-World Use

The significance of electric bike motor power in real-world use is primarily reflected in the following aspects:

• Performance and Energy Consumption: Motor power is a key factor in determining the performance of an electric bike. Higher power typically translates to stronger acceleration and hill-climbing ability. However, higher power can also mean greater energy consumption, which affects the electric bike’s range.

• Power and Speed: Motor power directly affects the top speed of an electric bike. In many countries and regions, the top speed of electric bikes is limited by law. For example, some areas may restrict electric bikes to a maximum speed of 25 km/h (15 mph).

• Power Levels: Electric bikes are often categorized into different classes based on their motor power. These classes may affect where the electric bike can be used, such as whether it can be used on bike paths or whether a license is required.

• Range: Motor power has a significant impact on the range of an electric bike. Lower-powered electric bikes may have a longer range because they consume less energy under the same battery capacity.

• User Needs: Choosing the right motor power depends on the user’s specific needs. For instance, commuting may not require a high-powered motor, while long-distance rides or hilly terrain may demand more power.

Examples of Electric Bike Power in Real Life

To help you better understand the practical implications of electric bike power and torque, consider these everyday scenarios:

• Starting and Accelerating: Imagine you’re waiting at a red light. When the light turns green, an electric bike with high torque can provide a strong burst of acceleration, allowing you to get up to speed quickly.

• Hill Climbing: When you’re cycling uphill, an electric bike with high torque can make it easier to climb, even on steep inclines.

• Hauling Cargo or Passengers: If you need to carry extra cargo or passengers, a high-powered electric bike can handle this added load without sacrificing speed.

• Range: For those who prefer longer rides without frequent charging, a lower-powered electric bike with a larger battery capacity can provide a more extended range.

Does a Higher-Powered Motor Consume More Electricity Than a Lower-Powered Motor Under the Same Load?

Under the same load, a 1000W motor will generally consume more electricity than a 500W motor. This is because higher-powered motors may have lower efficiency when providing the same output, resulting in greater energy consumption. However, it also depends on the motor’s design and efficiency. If two motors have the same efficiency, the higher-powered motor may not necessarily consume more electricity under the same load.

For example, a 1000W motor and a 500W motor might both be designed to handle the same load. The 1000W motor could be operating under less stress than its maximum capacity, potentially resulting in actual power consumption closer to that of the 500W motor. However, if both motors are running at their maximum power, the 1000W motor will consume more electricity.

On the other hand, if you frequently need to haul heavy loads or climb hills, a higher-powered motor can prove more beneficial. A lower-powered motor might overheat or struggle under prolonged overload conditions, while a higher-powered motor can handle these demands more effectively.

Additionally, the motor’s design and operating environment also influence its power consumption. Factors such as the motor’s efficiency, controller optimization, and battery management system can all impact energy usage. Therefore, while higher-powered motors may theoretically consume more electricity, real-world scenarios can vary depending on design and operating conditions.

Here is a table to help consumers choose the right e-bike motor power, based on the factors discussed:

Although there are even higher than 750W power options like 1000W, 1500W, and 2000W out there on the market, we limit it to 750W to suit the legal status of America in this case.

Additional considerations:

E-bike class: In many countries, e-bikes are classified by their maximum motor power and speed. Be sure to choose an e-bike that complies with the regulations in your area.

Battery capacity: The battery capacity will determine how far you can ride on a single charge. If you plan on riding long distances, you will need an e-bike with a large battery.

Motor type: There are two main types of e-bike motors: hub motors and mid-drive motors. Hub motors are less expensive, but mid-drive motors provide better power delivery and handling.

Test ride: Before you buy an e-bike, be sure to take it for a test ride. This will help you get a feel for the bike and make sure that it is a good fit for you. 

What is Torque in Electric Bikes

The torque of an electric bike refers to the rotational force generated by the motor when it is running. It directly affects the motor’s efficiency and power output. The greater the torque, the stronger the electric bike’s acceleration performance, hill-climbing ability, starting power, and carrying capacity.

Picture yourself standing before a towering mountain, its peak beckoning you to conquer its incline. As an avid hiker, you’re ready for the challenge, but you’re also aware that the ascent will demand a significant amount of effort. Now, imagine you have a trusty companion by your side – an electric bike, its motor humming with the promise of assistance.

The key to your electric bike’s ability to aid your uphill journey lies in the concept of torque, the rotational force generated by the motor. Think of torque as the raw power that propels the bike forward, akin to the muscular strength that drives your own legs as you climb.

Just as your muscles work harder when tackling steeper slopes, the motor’s torque output increases to match the demands of the terrain. This surge in torque is like an extra boost of energy, enabling you to power up the incline with greater ease and efficiency.

The Maximum Torque: Who Makes the Call?

The maximum torque of an e-bike is primarily determined by the motor’s design and the battery’s output current. Torque is the rotational force generated by the motor when it runs, and it directly affects the motor’s efficiency and power output. The formula for calculating torque is:

Torque = Power(W) * 9.549 / Output speed(RPM)

Therefore, torque is closely related to output power and output speed. The motor’s performance is also affected by factors such as speed, efficiency, design, and manufacturing quality. In an e-bike’s drive system, the motor, battery, and controller work together to determine the overall performance of the e-bike.

In general, a motor with higher power can theoretically provide greater torque, but this also depends on the motor’s design and the battery’s capability. Battery capacity and voltage determine how much current the battery can provide, and the current directly affects the motor’s torque output. Additionally, the controller’s design also affects the performance of the e-bike, as it controls the amount of current to each component of the e-bike.

Overall, the maximum torque of an e-bike is jointly determined by the motor’s design, the battery’s output current, and the controller’s configuration.

Inside the Motor: What Design Factors of an E-Bike Motor Affect Its Torque?

The torque of an e-bike motor is influenced by several design factors, including:

• Motor type: Different types of motors (such as brushless DC motors and brushed motors) have different torque characteristics.
• Motor size: Generally, the larger the motor, the greater the torque it produces.
• Magnet material: The quality and type of magnet material used in the motor affect its torque output.
• Winding design: The configuration of the motor windings (such as the number of coils and their arrangement) affects the torque.
• Rotor design: The geometry and mass distribution of the rotor affect the motor’s torque and inertia.
• Gearbox component: Many e-bike motors are equipped with a gearbox to increase torque and reduce speed.
• Control module: The motor’s control module determines the distribution of current, which in turn affects torque output.

In addition, the motor’s torque is also related to factors such as battery performance and capacity, vehicle weight, and tire friction coefficient.

The Importance of Torque in E-Bike Use

Torque is very important when using an e-bike because it directly affects the e-bike’s performance and riding experience. Here are some of the key roles of torque:

• Acceleration performance: The greater the torque, the better the e-bike’s acceleration performance. This means the e-bike can reach the desired speed from a standstill more quickly.
• Hill-climbing ability: High torque can help e-bikes climb hills more easily, especially when facing steep slopes.
• Starting power: When starting or riding at low speeds, torque is the main factor in providing power, helping the e-bike start smoothly.
• Carrying capacity: Torque affects the e-bike’s carrying capacity, as e-bikes with high torque can carry heavier loads.

What is a good amount of torque on an ebike?

Selecting the appropriate torque level for an e-bike depends on various factors, including individual riding preferences, terrain, and intended usage. However, in general, a good torque range for an e-bike falls between 50 Nm and 80 Nm.

Factors Influencing Torque Requirements

• Riding Style and Terrain:
  • Recreational Riding on Flat Terrain: For leisurely rides on paved paths or gentle slopes, a torque range of 40-50 Nm might suffice.
  • Commuting and Moderate Hills: For daily commuting and occasional hill climbing, a torque range of 50-60 Nm is suitable.
  • Mountain Biking and Steep Hills: For tackling challenging off-road terrain and steep inclines, a torque range of 60-80 Nm is recommended.
• E-bike Weight and Carrying Capacity:
  • Lighter E-bikes and Smaller Loads: For lightweight e-bikes or carrying minimal loads, a lower torque range of 40-50 Nm might be adequate.
  • Heavier E-bikes and Larger Loads: For heavier e-bikes or carrying heavier loads, a higher torque range of 60-80 Nm is necessary to maintain performance.
• Rider’s Physical Ability:
  • Stronger Riders: For stronger riders who can contribute more pedaling power, a lower torque range might be sufficient.
  • Less Experienced Riders or Riders with Limited Leg Strength: For less experienced riders or those with limited leg strength, a higher torque range can provide additional assistance.

Torque Recommendations for Different E-bike Types

• City E-bikes and Commuter E-bikes: 40-60 Nm
• Hybrid E-bikes and Trekking E-bikes: 50-70 Nm
• Mountain E-bikes and Off-road E-bikes: 60-80 Nm

Overall, torque is an important indicator of an e-bike’s power performance, as it determines the e-bike’s performance on different terrains. Therefore, when choosing an e-bike, it is important to consider the amount and characteristics of torque. High-torque e-bikes generally offer a better riding experience and stronger practicality.

Torque and Acceleration on E-Bikes

What are the typical weights and torques of e-bikes with 500W and 1000W motors?

E-bikes with 500W motors typically weigh between 20 and 28 kilograms, while e-bikes with 1000W motors are heavier, around 28 to 35 kilograms. As for typical torque, this data can vary depending on the different e-bike brands and models, but in general, the torque of 500W motor e-bikes may be between 40 Newton meters and 60 Newton meters, while the torque of 1000W motor e-bikes may be between 60 Newton meters and 80 Newton meters.

Please note that these are general estimates, and the specific weight and torque may vary depending on the specific design of the e-bike, the materials used, the battery capacity, and other factors.

According to the latest data, the average weight of an adult male in the United States is approximately 89 kilograms (about 196 pounds).

How do these two accelerations feel to a normal person?

For an average person, the difference in acceleration between 500W and 1000W motors is significant in terms of feel. The 500W motor provides an acceleration of approximately 4.42 m/s², while the 1000W motor provides an acceleration of approximately 8.33 m/s². This means that the acceleration of the 1000W motor is almost twice that of the 500W motor.

In real-world experience, this difference would make the 1000W e-bike feel like it starts and accelerates much faster. This acceleration feeling is similar to riding a more powerful car or motorcycle. For the rider, this could mean faster response times and a stronger sense of “pushback,” especially when accelerating from a standstill.

However, it is important to note that higher acceleration can also mean the need for better control and riding skills, especially in urban traffic or crowded road conditions.

The Role of Torque Arms in High-Power or High-Torque E-Bikes

Torque arms are very important for high-power or high-torque e-bikes, and their main functions include:

• Preventing motor rotation: In high-torque situations, the motor may generate rotational force at its mounting point. The torque arm can prevent this from happening and ensure that the motor remains in place.
• Protecting the frame and wheels: Torque arms help distribute the forces generated by the motor, reducing stress on the frame and wheels and preventing damage.
• Improving riding safety: By stabilizing the motor’s position, torque arms improve riding safety, especially when accelerating or climbing hills.
• Extending e-bike lifespan: Reducing the damage caused by high torque to the e-bike helps extend its lifespan.

Overall, torque arms are an important safety feature on high-power e-bikes, ensuring motor stability and overall vehicle durability. For e-bikes equipped with powerful motors, using torque arms can effectively enhance the riding experience and safety.

Are torque arms and torque sensors the same thing?

No, torque arms and torque sensors are two different components that have different functions and applications in e-bikes.

• A torque arm is a mechanical device that prevents the motor of an e-bike from causing damage to the wheels or frame when it generates a lot of torque. It is usually mounted between the motor and the frame, helping to distribute the forces generated by the motor and protect the frame from damage, especially when using high-power motors.
• A torque sensor is a measuring device that detects and measures the torque on the motor or other rotating components of an e-bike. It typically uses strain gauges or other sensing techniques to detect the torque applied to the shaft and convert it into an electrical signal. Torque sensors are used in e-bikes to precisely control the motor’s output, providing a smoother and more intuitive riding experience.

In general, torque arms are used to protect the mechanical structure, while torque sensors are used to measure and control torque. Although both are related to torque, their functions and application scenarios are completely different.

Key Takeaways of Torque:

What is torque in electric bikes?

Torque is the rotational force generated by an electric bike’s motor, directly affecting its performance and power output. Higher torque means better acceleration, hill-climbing ability, starting power, and carrying capacity.

Factors affecting torque

• Motor design: Different motor types (brushless DC, brushed, etc.) have varying torque characteristics. Brushless DC motors generally offer higher torque.
• Motor size: Larger motors typically produce more torque.
• Magnet material: The quality and type of magnets used impact torque output.
• Winding design: Coil configuration (number, arrangement) affects torque.
• Rotor design: Geometry and mass distribution influence torque and inertia.
• Gearbox: Many e-bikes have gearboxes to increase torque and reduce speed.
• Control module: Controls current distribution, affecting torque output.

Battery and controller influence

• Battery capacity and voltage: Determine the current supply, directly affecting torque output.
• Controller design: Manages current flow to various components, impacting performance.

Overall, torque is determined by motor design, battery output current, and controller configuration.

Design factors affecting torque in e-bike motors

• Motor type: Brushless DC motors generally offer higher torque than brushed motors.
• Motor size: Larger motors typically produce more torque.
• Magnet material: High-quality magnets enhance torque output.
• Winding design: Optimized coil configuration increases torque.
• Rotor design: Efficient rotor design improves torque and reduces inertia.
• Gearbox: Gearboxes can amplify torque and reduce motor speed.
• Control module: Advanced control modules precisely manage torque output.

Importance of torque in e-bike usage

Torque significantly impacts the e-bike riding experience:

• Acceleration performance: Higher torque enables quicker acceleration from a standstill.
• Hill-climbing ability: Strong torque facilitates easier climbing on steep inclines.
• Starting power: Adequate torque ensures smooth starts and low-speed maneuvering.
• Carrying capacity: High torque allows carrying heavier loads without compromising performance.

Torque and acceleration on e-bikes

• 500W motors: Typical torque range: 40-60 Nm; acceleration: 4.42 m/s²
• 1000W motors: Typical torque range: 60-80 Nm; acceleration: 8.33 m/s²

Torque arms in high-power or high-torque e-bikes

Torque arms play a crucial role in high-power or high-torque e-bikes:

• Prevent motor rotation: Counteract rotational forces generated by the motor.
• Protect frame and wheels: Distribute forces, reducing stress and preventing damage.
• Enhance riding safety: Stabilize motor position, improving safety during acceleration and climbing.
• Extend e-bike lifespan: Minimize damage caused by high torque, prolonging e-bike life.

Torque arms vs. torque sensors

• Torque arms: Mechanical devices that prevent motor-induced damage to wheels or frames.
• Torque sensors: Electronic devices that measure torque on the motor or other rotating components.

Torque arms protect the mechanical structure, while torque sensors measure and control torque.

Additional points

• E-bike weight: 500W: 20-28 kg; 1000W: 28-35 kg
• Average US male weight: 89 kg
• Higher torque generally means a better riding experience and stronger practicality.

Conclusion: Power and Torque of E-Bikes

Power refers to the work done by an electric motor per unit of time, measured in watts (W). The higher the power of an electric bicycle motor, the stronger the power it provides, enabling higher speeds and better hill-climbing ability. According to the new national standard, the maximum power of an electric bicycle motor should not exceed 400 watts.

Torque refers to the rotational force that an electric motor can provide, measured in newton meters (N·m). The higher the torque of an electric bicycle motor, the stronger its starting and acceleration capabilities, especially when climbing hills or carrying loads.

Relationship between Power and Torque

Power and torque can be converted using the following formula:

Power = Torque × RPM / 9549

where RPM is the rotational speed in revolutions per minute.

As can be seen from the formula, power and torque are directly proportional, and the higher the RPM, the higher the power. However, in practical applications, the power and torque of electric bicycle motors are not always the higher the better.

How to Choose the Right Motor Power and Torque

The choice of power and torque for an electric bicycle motor should be based on a comprehensive consideration of the following factors:

• Rider’s needs: If the rider frequently needs to climb hills or carry heavy loads, they should choose a motor with higher torque. If the rider primarily rides on flat terrain, they can choose a motor with lower power.
• Road conditions: If the riding conditions are relatively flat, a motor with lower power can be chosen. If the riding conditions are more complex, a motor with higher power should be selected.
• Range: Motors with higher power also consume more electricity, which can reduce the range. If the rider has range requirements, they should choose a motor with lower power.

In general, for ordinary riders, a motor with a power of around 250 watts and a torque of 30-40 NM can meet daily riding needs.

henry

Marketing and Sales Manager at Jieli Electric | Website | + posts

Sales Manager at Jieli Electric Bikes.
Near 10 years experience in electric bike industry, researching/marketing/promoting e-bike is my daily life.

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