How do you compare the torque of a mid-drive and hub motor?

What is the torque of the motor?

Hub motors (like Van Raam's motors) have a long lifespan. However, many e-bikes have a mid-drive motor, which always has a higher torque than the hub motor. However, you should not compare these torques one-to-one.

The power of the motor is called the torque, which is expressed in Newton metres (Nm). 10 Newton is equivalent to 1 kg. Suppose a motor has 100 Nm and you attach a 1-metre stick to the motor, it can lift 10 kg at the tip of the stick.

The torque of a hub motor is measured on the motor shaft, around which the motor rotates. With a mid-drive motor, the torque is measured on the crankshaft. This is why the motors cannot be compared one-to-one. Important to mention is that the torque is independent of the circumference of the wheel. So it does not matter for the torque whether the motor drives a large or a small wheel.

Comparing the torque

To compare force, one must look at the force at the same point. This article looks at the force on the driven wheel. This is the force the bike can actually produce.

So if you want to compare torque, you need to calculate the torque on the driven wheel. For bikes where the hub motor is inside the wheel, this is easy. This is equal to the torque of the motor. For bikes where the hub motor drives the wheel via a chain, you need to take the gear ratio (how fast does one sprocket turn relative to the other) between the sprockets on the motor and the wheel into account.

The same is also the case for the mid-drive motor, only then the gear ratio between the crankshaft and rear wheel must be taken into account. The gear hub must be taken into account here. This is because the hub, due to shifting, has a negative impact on the torque.

Easy Rider tricycle with hub motor compared with 2 mid-drive motors

See the torque graph of the Easy Rider tricycle compared to 2 mid-drive motors.

In the graph, you can clearly see that the torque of the mid-drive motor with 85 Nm is stronger in the beginning, but at higher speed, the torque becomes lower and lower and even falls below the torque of the hub motor. This takes shifting into account; at a pedal speed of 40 RPM (RPM stands for revolutions per minute), it switches to the next gear. 40 RPM was chosen because this is what is cycled a lot by Van Raam's target group.

It also shows that a mid-drive motor of 48 Nm is somewhat stronger than a hub motor over the entire course of the torque but only for a short time. With the Bosch CX, you have a bit more power up to 5 km/h, but after that you will experience less power as with an Easy Rider tricycle with a hub motor.

From a cycling speed of about 6 km/h onwards, the torque of an Easy Rider with hub motor is stronger than a mid-drive motor.

In summary, how do you compare the torque?

If you want to compare the torque of a mid-drive motor with the torque of a hub motor, you can't do it one-to-one. You will have to convert the torque of the motor to the torque on the driven wheel, including all gear ratios. In addition, with a hub motor it is important to take the gear hub into account and what gear it is in.

At a higher speed, the torque of the Van Raam motors is stronger than the torque of a mid-drive motor.

Why a front or rear hub motor instead of a mid-drive motor?

At the Van Raam bicycles, the motor of the pedal assistance is located in the front wheel, in the rear wheel or on the rear axle between the wheels. But why is this? And what is the advantage of a front hub motor, motor on the rear-axle and a rear hub motor vsmid-drive motor? Read all about it in this article 'Why a front or rear hub motor instead of a mid-drive motor?'.

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