The Perfect Electric Bike: Newton Meters Explained

Electric bikes have become increasingly popular, and with them, a host of technical specifications to consider. One of the most important factors to consider when purchasing an e-bike is its power, which is often expressed in Watts (W) and Newton meters (Nm). The number of Newton meters an e-bike should have depends on its intended use and the rider's needs. For example, a higher number of Newton meters will provide more torque, which is beneficial for climbing hills, carrying cargo, or accelerating from a standstill. On the other hand, too much torque may be impractical for city riding, as it could make the bike harder to control. Therefore, it's essential to find the right balance between torque and motor power to suit your specific needs.

Electric bike torque and power

Torque

Torque is the rotational force that powers the motor of an e-bike, enabling it to move forward. It is measured in Newton meters (Nm) and indicates the driving strength and acceleration capability of the bike. A higher torque value means faster acceleration and easier hill climbing, as it provides more force to the pedals. The ideal torque for an e-bike depends on its intended use; for example, riding on city streets requires different torque settings than climbing mountain trails. A typical e-bike has between 40 and 100 Nm of torque, with 40 Nm being sufficient for most urban hills while keeping acceleration smooth.

Power

Power, measured in watts, determines the velocity and functionality of the e-bike. It represents the speed and endurance of the motor, indicating how quickly it can deliver torque and sustain performance. A higher power output means higher speeds, quicker acceleration, and improved hill-climbing abilities. Most road-legal e-bikes have a power output of up to 250 watts, although some regions allow up to 300 watts. Peak watts refer to the maximum power the motor can generate in short bursts, which is beneficial for tackling steep climbs and achieving quick bursts of speed.

The Relationship Between Torque and Power

The relationship between torque and power is crucial in understanding the overall performance of an e-bike. While torque focuses on climbing ability and acceleration, power provides the speed and endurance. A balance between the two ensures an enjoyable riding experience, with enough power for challenging terrain and efficient energy usage.

Factors Affecting Torque and Power

Several factors impact the torque and power of an e-bike, including the type of electric motor, gearing system, and layout of the bike. Mid-drive engines, for instance, typically offer greater torque than hub motors. Additionally, the voltage and amperage of the motor controller influence the peak power of the bike.

Newton meters and watts

The number of Newton meters (Nm) an electric bike should have depends on its intended use. Newton meters measure the force exerted by an electric bike's motor in supporting its rider while pedalling. In other words, it is the rotational force that powers the motor to move the bike. The more torque or Newton meters, the faster the acceleration and the easier it is to climb hills.

For example, 40 Nm provides enough power for most urban hills while keeping acceleration smooth and manageable. However, for steep climbs, more torque may be required. One rider commented that they need at least 50 Nm of torque to avoid exhaustion after 5 kilometres of climbing.

The electrical power of the motor is expressed in Watts (W), which is the power output of the motor. The mechanical power is expressed in Newton meters (Nm), which is the motor torque. Wattage indicates how quickly the motor can deliver torque and sustain performance.

Peak watts refer to the maximum power the motor can generate in short bursts, which is beneficial for tackling steep climbs and achieving quick bursts of speed. On the other hand, continuous power refers to the power that the motor can sustain continuously without overheating. Most e-bikes have a motor with a continuous power rating of 250 or 300 watts, although there can be a significant difference in peak watts between motor brands.

In terms of legal compliance, the wattage of an e-bike motor indicates its maximum speed. In the European Union, for instance, the maximum speed is limited to 25 km/h. Similarly, to be classified as a "bicycle" in most states, e-bikes are limited to 250 watts.

Battery capacity

The battery capacity of an electric bike, measured in watt-hours (Wh), is an important factor in determining the range and performance of the bike. A higher watt-hour rating indicates a larger battery capacity, which translates to a longer range per charge. For example, a 300Wh battery may be sufficient for short city commutes, while a longer-distance ride or more challenging terrain may require a battery with a capacity of 500Wh or more.

The relationship between battery capacity and range is straightforward: a larger battery will take you farther. However, just like a car, if you don't use the battery efficiently, it will drain more quickly. Several factors can affect the efficiency of your battery and, consequently, the range of your electric bike.

Firstly, the level of assistance required will impact battery efficiency. Electric bikes have different levels of assistance, and higher assistance levels require more power, resulting in faster battery drainage and reduced range. Therefore, if you regularly ride with higher assistance settings, you can expect your battery to drain more quickly.

Secondly, temperature plays a significant role in battery performance. Electric bike batteries, typically lithium-ion batteries, are sensitive to temperature changes and tend to perform less efficiently in colder conditions. Thus, you can expect to achieve a longer range on a warm, sunny day compared to a cold, winter day.

Additionally, tyre pressure is another factor that can influence your electric bike's range. Properly inflated tyres can help optimise your battery range, just as correctly inflated tyres improve fuel efficiency in cars. Therefore, maintaining the correct tyre pressure is essential to get the most out of your electric bike's battery.

It is worth noting that the weight of the electric bike itself can also impact its range. Generally, more powerful motors require larger batteries, which contribute to the overall weight of the bike. While a heavier bike may provide more power and assistance, it may also result in a reduced range due to the increased demand on the battery.

Weight

The weight of the rider is an important factor in determining the ideal amount of torque for an electric bike. Heavier riders will require more power and battery from their e-bike, as the motor will have to work harder to achieve the same results as a lighter rider. For example, a heavier rider might require at least 50 newton meters of torque to avoid exhaustion on long climbs, while a lighter rider might find 42 newton meters sufficient for an 8% incline.

The weight of the e-bike itself is also a factor in its performance. Heavier e-bikes with higher torque can be beneficial for climbing, but the extra weight can negatively impact speed and range. For example, a 26kg e-bike with 85 newton meters of torque can handle inclines of up to 8% with ease, while a lighter 20kg e-bike with 42 newton meters of torque can become painful on inclines of more than 9%.

The weight of any additional cargo should also be considered, as this will also impact the performance of the e-bike. More torque will be required to carry heavier loads, and the battery will drain more quickly.

It is important to note that the weight of the rider, the e-bike, and any cargo will all contribute to the overall weight that the e-bike's motor has to support. As such, it is crucial to consider the weight of all these factors when determining the ideal amount of torque for an electric bike.

Speed

The number of newton meters an electric bike should have depends on its intended use and the rider's preferences. Newton meters measure the force exerted by the motor in supporting the rider while pedalling, with higher values indicating greater force and faster acceleration. For example, a 40 Nm rating provides enough power for most urban hills, while a higher rating of 60-90 Nm is better suited for off-road riding or cargo hauling.

The relationship between speed and newton meters is influenced by several factors. Firstly, the motor's wattage (watts) determines its maximum speed and legal compliance, with most states and European legislation limiting e-bikes to 250 watts. Secondly, the torque, or newton meters, affects the bike's acceleration and hill-climbing ability. A higher torque rating enables faster acceleration and easier climbing, which can be advantageous in urban environments with frequent stops or hilly terrains.

When considering speed and newton meters, it's important to balance motor power, torque, and pedalling style. While a higher torque can improve acceleration, it may not always be necessary for maintaining speed on flat surfaces. Additionally, other factors such as battery capacity, tyre pressure, and tread can impact the overall speed and range of an electric bike.

In summary, when choosing an electric bike, it's essential to consider the intended use and desired speed. While newton meters are crucial for acceleration and climbing abilities, they should be balanced with other factors to create an enjoyable and efficient riding experience.

Frequently asked questions