What aspects of performance should we pay attention to when we choose an e-bike？

Popular Science: What aspects of performance should we pay attention to when we choose an e-bike?

With the popularity of electric assist, more and more cyclist choose e-bikes as their daily transportation. In order to give everyone a basis for choosing an e-bike, we consulted electrical engineers from Bafang, an electric-assisted drive system brand, about the geometric design of the e-bike and the power, torque, cadence, and battery capacity of the drive system. To answer your doubts about the e-bike selection process.

Geometric design

Electrically assisted bicycles follow the geometric design concept of modern bicycles, but the addition of three-electric systems brings more difficult challenges to designers. In terms of frame design, the difficulty in electric-assisted design lies in overcoming the weight brought by the battery and motor. , physical limitations in space, and other aspects. For example, the design of the position of the motor and battery, the reinforcement of the frame strength, the arrangement of the frame holes and cables, the reservation of storage space, possible interference problems in the shock absorber position, etc., excellent frame design will comprehensively study such complex problems and provide optimal solutions.

The significant change brought about by the addition of electric assist systems is the increase in the weight of the entire vehicle. How to effectively reduce weight is also an important issue that needs to be solved urgently for mid-to-high-end electric-assist mountain bikes. Lightweighting has always been an important direction of change for the continuous updating and iteration of electric assist.

Under the same conditions, lighter weight brings less power consumption, longer battery life, easier climbing experience, stronger kinetic energy output, better control, and a ride that is closer to the integration of humans in the original bicycle. 

Among the three major parts of the motor system, the battery and the motor account for the highest weight. The main parts of the motor include the stator and rotor, reducer assembly, control module, axis, casing, etc. The battery is composed of battery cells, BMS management systems, casings, etc. Composition, without sacrificing motor performance and reducing battery capacity, it is very difficult to reduce some weight from these two parts.
 

In addition to lightweight structural design, the performance level of the drive system is also a matter of great concern. The following analysis will focus on power, torque, cadence, and battery capacity to provide more basis for judgment when choosing an e-bike.

How to judge the performance of an electric power-assisted drive system - Power 

First, let us understand the working principle of an e-bike: when the cyclist starts to pedal the bicycle, the electric assist system will sense it through the torque sensor and control the intelligent algorithm to start the motor. The motor is driven by gears and then decelerated through the reducer assembly to match the person's cadence to drive the wheels to rotate, thereby providing the cyclist with natural and stable auxiliary power.

The performance of a motor is usually judged by reference to two parameters: rated power and peak power. The rated power is the continuous power output of the motor under normal operating conditions, which represents the stable working ability of the motor, while the peak power represents the maximum power output of the motor when the load requirement increases instantaneously or briefly, which is temporary and instantaneous.

The duration of high power output of the motor is related to the motor power density, heat dissipation design, etc. Improving the duration is a very complex project.

In addition to power, motor performance is affected by multiple factors such as speed, torque, efficiency, and design and build quality.

Currently, there are huge differences in the maximum torques marked by different types of motor systems on the market based on the needs of different riding scenarios. The maximum torque is usually a comprehensive value formulated based on the needs of R&D, sales, marketing, and other parties. However, in order to cater to the market's pursuit of high torque, some motor manufacturers have created "false propaganda" with empty data and a much weaker actual riding effect.

However, it is difficult to judge whether this motor is really powerful simply by looking at the paper data. It does not have much practical significance other than proving that the motor rotates harder on the machine.

How to judge the performance of an electric power-assisted drive system - Cadence

When we ride an ordinary bicycle and rely solely on our thighs for output, all "cycling veterans" will remind us to pay attention to our cadence and maintain stable output. The same is true for electric assist.

Electric assist is a hybrid of human pedaling + motor assistance. It highly relies on accurate torque sensors and internal algorithms to adjust the size of the motor output in real-time. The information collected by the torque sensor comes from the power output of each pedal step.

Maintaining a stable cadence will improve the operating efficiency of the motor. For example, the Bafang M510 motor extends the maximum cadence to 120rpm. It can still maintain the smoothness of the power even when a high cadence is required for continuous pedaling output and can maintain smoothness when riding at high speed or climbing slopes. Higher speed and power output bring the ultimate riding experience.

How to judge the performance of an electric power-assisted drive system - Battery Capacity

Generally speaking, there are two ways to express the battery capacity: one is the battery capacity at a rated voltage in Ah, and the other is the factor that takes into account the voltage change of the discharge curve, which is marked as rated voltage X battery The battery energy of the capacity is expressed in Wh, such as 630Wh, 720Wh, etc. The expression of battery energy (Wh) is theoretically more accurate and comprehensive.

Battery capacity determines the battery life of the electric assist. Under the same rated voltage and power, a larger battery capacity means a longer mileage and a more durable battery life. However, a battery with an excessive capacity will increase the cost and cause inefficiency. Avoid increasing the weight of the vehicle.

At present, electric power assist will select batteries of appropriate capacity according to the usage scenarios and purposes of different models. However, some long-distance travel vehicles, freight trucks, snowmobiles, and other models that have higher requirements for battery life and have a large amount of redundant space in the body structure will be equipped with Ultra-large-capacity batteries; however, high-end sports mountain bikes and road bikes will strictly control the battery capacity due to the weight of the vehicle. Generally speaking, the standard 720~750Wh battery is already a high-capacity level among full-suspension softtails.

In summary, an excellent electric power-assist system should have high-quality materials and precision manufacturing capabilities, efficient, easy-to-use, and controllable auxiliary power, and safe, intelligent, and reliable intelligent algorithms. It is a big competition between comprehensive strength and actual riding experience. Although higher power, cadence, and torque usually mean higher riding speed and better power output, as well as considering the overall performance of the motor. These factors will affect the performance of the electric assist system in various mountain road conditions.

With the continuous development of e-bikes at home and abroad, electric assistance will be the leading force in the development of the entire bicycle market in the next 10 years. We also look forward to witnessing more and more electric assistance bicycles entering our daily lives.

We hope this article can provide e-bike enthusiasts with a reference when choosing an e-bike. If you have any questions or business cooperation, please CONTACT US.