When it comes to an eBike, one of the most important components is the motor. Not all motors are made alike though, and unfortunately not all motors are expressed the same way. Some companies list just the Amp Hours, some just list the Watt generation, while others are more direct and express the total torque or Newton-meters. Understanding what kind of motor you get can be difficult to understand if you don’t understand these measurements, although we do our best to break it down in our reviews here at Best Electric Bikes. If you’re looking at a motor we haven’t reviewed, or just want to learn more about motors in general, here are some of the important things to know when it comes to motor size on eBikes!
How are Motors Measured?
To begin, we want to make it clear that the actual physical dimensions of a motor don’t matter that much. We’ve reviewed some motors that were twice the strength of another motor, despite being only half the size. Instead, you will want to understand these terms to start to get a basic understanding of how motors are measured: Volts, Amps, Amp Hours, Watts, Watt Hours, and Newton-meters.
Volts: Volts is a measurement of the force or rate of flow of electric power flowing through a current at any given time. Comparing it to a faucet, think of volts as how fast a stream of water is moving through a faucet.
Amps: Amps is a measurement of how much electrical power is flowing through a current at any given time. Comparing it to a faucet, think of amps as the total amount of water flowing down the tube.
Amp Hours: Amp hours, or Ah, is one way to measure the total energy capacity of a battery. More specifically, the Ah measures how much current can be delivered in one hour at a certain voltage. Returning to our faucet comparison, it would be the total water that will flow out of the tube before it is completely empty.
Watts: Watts is a measurement of volts multiplied by amps, or V multiplied by A. Watts is the traditional measurement of the total amount of power that a motor has. Thinking about it like a faucet, the watts is the total force behind the flow of water as it comes out of the faucet tube.
Watts Hours: Watts is a similar comparison to Amp Hours, but instead of measuring the total energy capacity it measures how many watts, or how much power, is delivered over the course of a single hour. If you think about Watt Hours in terms of a faucet, then Watt Hours is the total force generated by the stream of water over the course of one hour. Watt Hours are generally given for batteries instead of motors, but sometimes a motor is expressed as a Wh measurement as well.
Newton Meters/Torque: Newton meters are a unit used to measure the total torque that can be generated by a motor. Torque refers to the total force generated by an object turning in a linear rotation. If you wanted to apply torque to a faucet, the torque would be the total force generated by the water as it spun around the tube.
Those are the major terms that you want to be aware of when it comes to understanding electric bikes. So, how do we actually apply these terms? Well, there is some good news and bad news in that regard.
The Importance, and Lack Thereof, of Understanding Motor Power:
Generally speaking, Watt (W) and Newton Meters (Nm) are the two most useful ways in understanding the total power of a eBike motor. The larger the number is, the stronger the motor will be. Some companies like to use Watt Hours, while others like to use Newton Meters: while they both describe different outputs, they both are an effective way to measure the power generated by an eBike motor. If you can’t find either the W or Nm of a motor, you can calculate the total watts generated by the motor by multiplying the volts by the amps.
The biggest problem with the eBike industry is that companies have yet to standardize whether they’re referring to peak output or continuous output. That’s why even though some eBike manufacturers make a motor rated for 75 Nm, it may actually be less powerful than other motors that have a 50 Nm rating. For this reason, finding trusted and verified reviews of eBikes is still the best way to determine the overall performance of a motor, though you can also find out the exact performance by asking about whether the ratings are for continuous or peak usage.
So What Size of Motor Do I Need for My eBike?
The overall motor size you need for your eBike is going to depend on what you intend to use your eBike for. If you are just going to be riding over smooth paved roads in the city, your motor doesn’t have to be nearly as powerful as the motor that you need for riding over a steep mountain bike trail. The level of pedal assistance, range, and cost are all factors that you have to consider too beyond just motor size. While you can buy an extremely powerful motor it will cost you and may drain your battery so quickly, you can’t travel more than a few miles before your battery is dead.
As such, what we recommend is that when you’re upgrading your eBike, upgrade the battery before you try to replace the motor. A larger battery will extend your range, allowing you to travel farther or use the more power-intensive turbo mode for a longer stretch of time. Generally, buying an eBike from a trusted eBike manufacturer brand will result in you getting a motor that is rated for the type of activity you engage in.
If you do want to try throwing on a custom motor though, here are some general ratings that will help you get a good start of what to look for:
General eBike Motor Size Recommendations:
- City Bicycles: 250 W / 40 Nm minimum
- Cruiser/Cargo Bicycles: 350 W / 50 Nm minimum
- Mountain Bicycles: 450 W / 60 Nm minimum
- Speed Bicycles: 500 W / 65 Nm minimum
Conclusion: Read a Review, or Consult an Expert:
Motors are at the heart of every eBike, but they are one of the most complicated components to understand. We just went over a few key aspects to motors, but we haven’t even discussed how mid-drive motors are different from hub-drive motors, how different chains and belts impact performance, and how CVT motors are changing the game. Because of how much there is to know, we highly recommend consulting an expert or even leaving a comment on our site if you want to know about a specific motor’s performance. More often than not though, the stock motor that comes with your eBike should offer powerful performance, helping you travel far while making your ride easier thanks to the electronic motor power. Exciting new motors are coming out every year, so visit us again in the future to stay up to date on the latest trends in the eBike industry!