E-bike power ratings and how to choose correctly - it can be overwhelming.
In our E-bike overview article that's also on our site, we discuss the different types and even get into power differences on some of our bike comparisons.
In short, I'd look at it this way.
Mid Drive versus Rear Hub Drive Bikes
I won't get into all the pluses and minuses of the two types of bikes here, as we have another article that goes into the differences between the two. But they are typically measured differently when it comes to power.
First, we'll discuss the Motor Power Ratings of Rear Hub Driven Bikes:
Motor Power Ratings:
What do I recommend? If you're riding in Northwest Arkansas up and down the hills of the Razorback Greenway, I'd make sure my Rear Hub Drive E-bike has at least a 500W motor. I've ridden those with 350W and they don't me up the hills with the power that's needed. It just leaves something to be desired. They're fine for flatter terrain or if you simply want to work harder up the hills. I'd also say the market seems to be reflecting this, and 500W appears to be the standard many E-Bikes are now hitting.
When you see a rear hub motor rated at 500W with a peak power of 750W (or more), it means that the motor has a continuous power output of 500W, but can briefly provide up to 750W of power for short bursts.
Batteries on Rear Hub Driven Bikes
You'll see ratings like 400W, etc. Frankly, I think the market has settled in here and there's not much decision making on your part. The good quality brands are pairing an adequate battery with the right motor. You'll typically see a 500W motor paired with a 500W battery and so forth. It's just telling you how much continuous power the battery will put out over a period of time. The main thing here is to make sure you can get enough miles out of a charge. All E-bikes are not considered equal here. E-bikes with name brand batteries will typically get more mileage out of a charge than generic batteries.
Motor Power Ratings of Mid Drive Bikes:
When it comes to mid-drive electric bikes, the power output of the motor is often measured in Newton Meters (Nm) of torque, instead of watts. The torque is a measure of the twisting force that the motor can apply to the bike's drivetrain, and is an important factor in determining the bike's overall performance. Here is an overview of the motor power on mid-drive electric bikes, using the Nm standard:
Low-power mid-drive motors: These motors typically have a torque output of around 40 Nm. They are designed to assist the rider with pedaling, rather than providing all the power for the bike. This type of motor is suitable for relatively flat terrain or for riders who don't need a lot of assistance. These bikes will get you up and down our hills, but often without as must assistance as one would want in our area.
Mid-range mid-drive motors: These motors typically have a torque output of around 50-70 Nm. They are designed for more demanding riding conditions, such as steep hills or heavy loads. They can provide a significant boost to the rider's pedaling power, making it easier to tackle challenging terrain. Personally, if I'm riding on paved trails here, I like 50 Nm or more. For Mountain Biking, I think it needs to be at least 60Nm, to give the torque to be responsive enough to get up our hills. My current E-bike is a mountain bike with 60Nm of torque and is plenty for what I do. I am very much an intermediate rider.
High-power mid-drive motors: These motors can have torque outputs ranging from 80 Nm to 120 Nm or more. They are designed for the most demanding riding conditions, such as extreme off-road riding, heavy cargo hauling, or steep hill climbing. They provide a lot of power and torque, which can help riders tackle the toughest terrain. For some of the tougher mountain bike trails here, I'd recommend at least 80Nm of torque. I've been riding on a mid drive with
Batteries of Mid Drive Bikes
Again, just look at the range of the bikes you're considering, to see how many miles per charge they're rated. Don't be alarmed if you see a battery wattage rating on a mid drive bike that's significantly less than a rear hub drive bike. They can put a smaller battery that weighs less, and get more miles as the mid drive bikes are so much more efficient. My current mountain bike has 60Nm of torque and a 250W battery, which will get me 60 - 80 miles of pedal assist per charge and all the power I need.
Comparison of Mid Versus Rear Hub Drive
Overall, I'd say a 500W Rear Hub Drive motor is comparable to a 50Nm mid drive in terms of power output - sortof.
It's a bit difficult to directly compare a 500W rear hub drive electric bike motor and a 50Nm mid-drive electric bike motor because they are measuring different things.
The 500W rear hub motor is measuring the power output of the motor in watts, which is the amount of electrical energy being used by the motor to turn the rear wheel. The 500W rating is an indication of how much power the motor can produce at its maximum output.
On the other hand, the 50Nm mid-drive motor is measuring the torque output of the motor in Newton meters (Nm), which is the twisting force that the motor can apply to the bike's drivetrain. The 50Nm rating is an indication of how much force the motor can produce to help the rider pedal the bike.
So, while both ratings are important, they are measuring different aspects of the motor's performance. A 500W rear hub motor may have more power, but a 50Nm mid-drive motor may have more torque, which can be important for climbing hills or carrying heavy loads.
Essentially, a 500W rear hub drive will seem more powerful on level ground, while a 50Nm mid drive will feel more powerful on steep climbs. That's why you see many manufacturers have say a 500W rear hub motor, with peak power up to 750W (or more) to give it more of the punch you feel with a mid drive.