Torque Vs. Watts: E-Bike Essentials Simplified

So, you’re shopping around for an e-bike and getting lost in the cavernous rabbit hole of stats, figures, charts, and, worst of all, jargon. Your computer screen is filled with amps, wattage, torque, power, and amp hours. Still, your electrical engineering degree is missing from the wall. Before you short-circuit your brain, let us at least help you understand the difference between torque and watts.

Torque can be understood as rotational force, meaning that torque determines how well your e-bike will climb and accelerate. On the other hand, watts are a measurement of power, which refers to the amount of work a motor can do over time. More power equals a higher top speed.

That said, it’s not as simple as choosing a bike with either more torque or higher wattage. Instead, you need to understand how the two work together. And how focusing on one over the other can drastically affect your ride.

The Differences Between Torque And Watts

Although torque and watts (or power) interact closely, there are substantial differences between them that you need to understand when choosing a new ride.

Torque Is A Rotation Force

One of the easiest ways to understand torque is to picture a wrench. A wrench is used to apply a rotational force on a nut to either loosen or tighten it. You’ll probably fail if you try to loosen a tight nut with your fingers. So, you opt to use a wrench.

But the question is, what does that wrench actually do? Does the wrench somehow increase the strength your arm can apply? Obviously not. However, it moves your arm’s force further away from the central point, which is the nut. By moving the force further away, the twisting power is vastly increased.

This is similar to a lever, but the applied force is circular instead of just pushing up or down. And this is, in essence, how your e-bike’s gears work.

If you want to ride up a steep incline, you shift to your lowest numbered gear, which you may have noticed is physically the biggest rear gear. The force of your pedal strokes is applied to the axle, or center, of the rear wheel, and by shifting to a bigger-sized gear, you move the force further away, which increases the torque. Make sense?

So, if we want to increase torque, we can increase the distance at which the rotational force is applied, in the same way, that a longer wrench also increases leverage.

Applying more force is another way to increase torque. This is like asking someone stronger than you to open a jar. Their grip isn’t further away from the center of the lid, but their additional strength means they can apply greater force.

Watt Is The Amount Of Work Done Over Time

On the other end, we have wattage, also called “power.” The easiest way to understand power is that it basically refers to the amount of work a motor can do over a given period.

Let’s assume you have two e-bikes in a race, one with a 250-watt motor and the other with a 750-watt motor. The length of the race is five miles, meaning that the amount of work that each motor has to do is to move the bike and rider for a distance of five miles.

In this case, the motor with 750 watts will do that work faster because it has more power.

You might also wonder if a bigger battery could make your e-bike faster.

Not only can a more powerful motor do the same work in less time, but it can also do more work than a weaker motor. Or, to simplify, a bike with a more potent motor can carry more weight.

So, all things being equal, motors with higher watt outputs have higher top speeds than less powerful motors.

Should Your E-Bike Have Higher Watts Or More Torque?

Now that you hopefully understand the differences between the two concepts, you may wonder which is the more important to focus on.

Let’s go back to our two bikes that are in a race, and let’s assume that the 250-watt motor has 50 newton-meters (NM) of torque while the 750-watt motor has 25 NM. When the whistle blows for the race to start, the e-bike with more torque may be off the line a little quicker because it has a greater rotational force to get the bike rolling.

But the e-bike with the more powerful motor has a higher top speed and will quickly overtake it and win the race.

However, things would change if we were to move the race to a steep hill and gradually keep making the hill steeper toward the end. At some point, despite being technically more powerful, the motor with less torque won’t have enough rotational force to turn the wheels and will stop.

The torque of an e-bike significantly impacts its climbing ability. Find out whether an electric bike can tackle steep hills.

The less powerful motor could win because it can still turn the wheels, albeit very slowly.

That being said, torque can be compensated to a large extent with suitable gearing. If you have a wide gear range on your bike, you can dramatically increase the torque. This means that motors with higher watts are more likely to accommodate the average rider.

Be Careful Of False Marketing Watts

One of the common issues around the rather complicated jargon of e-bikes is that it, unfortunately, gives manufacturers a golden opportunity to profit from ignorance. Wattage is an area where this is relatively common practice because often, the advertised wattage of a motor isn’t necessarily the whole truth.

The power output of a motor is directly attached to its voltage or charge. Meaning that when a battery is fully charged, it will deliver more power to the motor due to the increase in voltage. As the battery depletes, the voltage decreases along with the motor’s power or its ability to do work.

The motor in an electric bike plays a crucial role in determining its torque and watts. Learn more about which motor is used in electric bikes.

So often, manufacturers will market a motor’s wattage at the absolute optimal point where the battery is fully charged and ambient temperatures are just perfect. But in reality, your experience may be completely different from the pamphlet.

Doing thorough research and not being swooned by the sweet words of corporations is always the best idea.

Conclusion

Torque refers to rotational or twisting force and influences how well an e-bike accelerates and climbs. More torque means that the bike can handle steeper hills. Watts, or power, determines the top speed of a bike and how much weight the motor can comfortably handle. Motors with more power will be faster than motors with lower power, even if the latter has more torque.

After understanding the relationship between torque and watts, you might be interested in how to increase torque on your e-bike.

Author

  • Miles Baxter

    Miles Baxter is an engineer with a longstanding love for bicycles, sparked by winning a mountain bike in a childhood lottery. Balancing a keen interest in mechanics with the thrill of biking, his career is a testament to the art of turning wheels and gears into adventures.

    Baxter Miles