How much torque should an electric bike have? This question is one of the most common questions asked by people who buy a new electric bike, or even from individuals who own electric bikes and plan to use their bike to pull a trailer or load heavy things.
In fact, this question is important because it opens the door to understanding and clarifying many things that are misunderstood in the world of electric bikes.
One of the most important things that are misunderstood is that the power of the motor depends on the number of watts only, and this is unrealistic.
For example, if you have a bike with a 500-watt motor, the performance may be higher than a bike with a 750-watt motor, because the torque in the 500 is higher than in The 700 watts, especially if it comes to riding on slopes or loading many things.
In this post, we will explain the difference between power and torque, and also what torque you may need in your electric bike.
I know that in order to explain this we will need to touch on some physics, but do not worry, we will explain the information with simple and easy practical examples so that you have enough information to decide which torque is appropriate for the conditions of your use of your electric bike.
What does torque mean in ebike world?
Torque meaning is the turning force of any object and it can be measured as Torque= force*distance.
Practical Example: If you have a nut and you want to loosen it with your hands, you probably won’t be able to, but if you use a wrench, you will loosen it, knowing that you used the same force that you used when you tried to loosen the nut with your hands.
The reason you can loosen the nut with the wrench is that the length of the wrench (distance) combined with the strength of your hands (force) creates greater torque.
But what does this mean in the world of electric bikes?
When converting the previous example of the electric bicycle motor, we will find that the motor has two main parts, the first is the copper wire and the second is a large magnet.
when you conduct an electric current through the copper wires, you create an electromagnetic force (which represents the force in the torque equation) and the length of the distance between the magnet and the middle of the motor represents the distance in the torque equation.
That’s why you will notice that the motors which have high torque somehow have a large size.
Now that we have explained what is the torque in an electric bike, let us know how much torque an electric bike should have?
How Much Torque Should An Electric Bike Have?
As a general rule, an electric bike should have a torque between 40 to 80 Newtons, taking into account the wind force, the total weight of the bike and the driver, as well as the degree of incline of the road, Pedaling & rolling resistance, as these factors, affect the amount of torque required
As we explained in the previous answer that there are several factors that affect the amount of torque that you may need in an electric bike, and in the next section we will discuss these factors with some illustrative examples.
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Driving force
Before we begin to explain these factors, there is a piece of information that you should know, which is that the Driving force = torque * RPM. This means that the total driving force generated by the electric bike will be affected by the factors that affect the torque, because the higher the torque, the higher the driving force of the bike.
The following picture shows multiple examples of several models of bicycles that have a torque between 40 Newtons and 80 Newtons, as well as a number of different driving forces.
As shown in the previous picture, the driving force changes according to the torque and the type of tire size for the electric bike.
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Now let’s move on to the elements that affect the torque of an electric bike.
1- Total Weight (ebike & Rider)
Weight is a very factor affecting torque, whether it is positive or negative. For example, if you are riding your electric bike uphill, the weight will affect you negatively, and consequently, you will need more torque to keep going, but if you are riding your bike towards the incline, it will increase the overall power of the bike
The following graph will help you to know the real percentage of your total driving force that you will lose if you go uphill.
In order to know this percentage, you need to know two things.
The first is the degree of incline on which you ride your bike, and the second is the total weight of the bike, driver, and anything else you carry on the bike.
To find out the slope of the ramp, you can use any of the free Apps on Smartphone stores
Examples:
If the total weight of the bike and rider is 350 lbs and the ramp is 5.7, then you will lose about 10% of the total driving force, which is equivalent to 35 lbs.
2-Wind Drag.
The second factor that affects torque is wind. When you ride your bike headwind, you will need more torque and driving force.
The following graph shows the amount of momentum lost when cycling at different speeds.
Example: If you were riding a headwind at 15 mph, the total driving force lost would be about 4 lbs.
3-Pedaling
Using the pedal while riding an electric bike increases the driving force while riding a bike and thus affects the amount of torque required.
If you are a fan of pedaling while riding an electric bike, you can dispense with a little torque because you will compensate by pedaling
In general, a cyclist can add a driving force equal to his weight, but it is noted that in order to reach this amount of driving force, you will have to stand while riding the bike.
4-Rolling Resistance.
The size of the bicycle tire is one of the factors that affect the torque coming out of the motor. The larger the tire, the higher the rolling resistance, as well as the type of road, is it paved or not.
In general, the driving force lost as a result of rolling resistance ranges from 2lbs to 8lbs.
Real Live Example To Calculate The Required Torque.
In this part, I will share with you an example from the real life of how to choose the right torque for your electric bike according to your use.
We will assume the following:
Weight:
I will use the electric bike to load some heavy items averaging about 50lbs plus the bike weighs about 50lbs and my weight as a cyclist is about 200 pounds.
The total weight is about 300 pounds
Slope
I live in an area with slopes of about 4.5 degrees.
Rolling resistance:
I prefer fat-tire bikes, so there will be an average loss of the driving force of about 7lbs
Wind: I ride my bike in windy weather at an average speed of 20 MPH
Pedal: I don’t like to use the pedal a lot while riding an electric bike, so I will add about 20 pounds of extra torque.
Now let’s calculate the torque and driving force Required
Riding uphill 24lbs + Rolling Resistance 7lbs + Wind 8lbs = 39lbs
This means that if I were to use my bike completely without the pedal, I would need about 39 pounds of the driving force.
But if I use pedal, I need about 19 pounds of the driving force.
So I will look for a bike that gives me a torque of at least 80 Nm to ensure that the bike will provide above 39lbs driving force.
Useful Resources.
How Do You Care For An Electric Bike Motor? (Explained) This post shows the correct way to maintain your ebike motor
External Resources.
