If you’re shopping for an electric bike or considering an upgrade from your manual bicycle, you’ll often encounter all kinds of jargon concerning the motors used on Ebikes. Whether it’s a graph displaying wattage vs. torque or a list of seemingly impressive statistics, or even the simple ‘750W’ plastered all over a bike’s webpage, it can often be hard to tell what this information actually translates to in the real world.
This article is designed to help DIY Ebike enthusiasts and those of you interested in finding out more about electric bike power levels, in general, to allow you to make better choices when it comes to buying or building your new ride. Whether you’re deciding between a hub motor or a mid-drive motor or trying to figure out just what on earth the hill-climbing potential of your new Ebike actually is, you’ll find the info to help you do so here.
A Quick History
For those really interested in how an electric bike motor works, it might be nice to know a little bit of history first. The engine on an Ebike, after all, is essentially the same kind used in various electric vehicles like trains, cars, and electric scooters. The original basis for this design comes from American inventor Thomas Davenport, who gave genesis to the DC electric motor back in 1834, using a system of electromagnets to rotate a small gear.
This design went from powering model railways and rudimentary miniature vehicles in Davenport’s time to eventually powering Frenchman Gustave Trouvé’s electric tricycle in 1880. This was one of the first working electric vehicles and spawned many successors, including Hosea W. Libbey’s double-motor electric bike in 1897. Electric bikes remained a novelty throughout the 1900s but reached the mass market after neodymium magnets were first discovered in the 1980s, allowing for mass production of powerful, cheap electric motors.
These magnets are still used in many Ebike motors today, including the famous Bosch Ebike systems that popularized electric cycling worldwide in the 2010s.
How do Ebike motors work?
The basic principles used in Ebike motors are surprisingly simple. To put things succinctly, modern Ebike motors work in much the same way as those made back in the 1800s, with an electromagnetic field being used to spin a rotor through the process of electromagnetic induction constantly. This essentially means an outer circle of magnets is charged with electricity, generating an electromagnetic field. This causes an interior ring of several smaller magnets to spin repeatedly, turning a rotor at the centre of the motor device, which in turn can be used to spin gears and wheels.
Originally, electric motors used AC power to constantly reverse the polarity of the exterior magnets, which is necessary to make the interior rotor spin consistently. This, however, required the use of brushes that would degrade over time due to the wear and tear of friction. These days, DC brushless motors, like those found in Ebikes, use a computer system to reverse the electrical current instead, flipping the polarity constantly without the need for delicate brushes. As a result, brushless motors rarely need any maintenance, as they work primarily through a contactless process.
Different Types of Motors
When shopping for Ebikes or Ebike parts, you’ll most often see three different types of motors: Mid-drive, Direct-drive, and Geared hub motors. Below, you’ll find an explanation of what each one is and how it differs from the others.
Electric bike mid-drive motors are rapidly becoming very popular in the consumer market. They’re a modern motor and in many ways quite different from the original wheel-hub Ebike motor. A mid-drive engine sits in the middle of the bike’s frame, around the bottom bracket and cranks. It’s connected to the drive cranks and chain and usually powers the bike via the rear wheel. As these motors are incorporated directly into a bike’s crankset, they’re significantly more efficient than traditional electric bike hub motors, as well as being both smaller and lighter. This all translates to a smooth ride, high torque, and great acceleration from dead stops.
All of this comes at a cost, of course. As mid-drive motors are connected to the rest of a bike’s functionality, they suffer from a lot of wear and tear. Using a mid-drive motor is like letting a professional athlete hammer your pedals for hours at a time, and so inevitably, mid-drive Ebikes require a fair bit of maintenance. Plus, if your mid-drive motor fails on a ride, you can’t pedal the bike back, as the chain will be non-functional too. Strictly in terms of performance, however, mid-drive motors often outpace wheel hub motors significantly.
Now let’s take a look at the traditional tech, with the direct-drive and geared hub motors. Both of these motors sit in the hub at the center of your bike wheel, with direct-drive electric bike motors being the simplest of the two types. These motors drive the wheel directly using a large magnetized hub, and as they’re self-driving, they require practically zero maintenance. They’re durable, fast, and quiet and one of the cheapest electric motor solutions out there.
Direct-drive motors do have some drawbacks, of course. They only have a single gear ratio, so they’re not especially effective for hill climbing, and this can also make cassettes with more than seven speeds unusable. There’s a little more drag, too, and the heavy motor hub means you’ll have less range on each battery charge than on a light mid-drive motor. There’s a caveat to this, however. If a mid-drive engine runs out of juice, it isn’t easy to pedal your bike back. However, if a direct-drive hub motor is drained, you can pedal the bike home as normal, even if it is a little heavier than a standard bicycle.
Geared Hub motors
The geared version of a direct-drive motor, geared hub electric bike motors once again sit at the center of a wheel but use a smaller setup than non-geared versions while also producing higher torque on the same wattage as a direct-drive motor. The addition of small moving parts multiplies your power by slowing down an otherwise high motor RPM. This does, however, mean that you’ll require some occasional maintenance, as this process wears down the gears’ teeth over time.
Geared hub motors strike a good balance between mid-drive and direct-drive engines in this way. They have less drag than a direct-drive motor, and they’re smaller but not quite as stealthy as mid-drive motors. For starters, they make more noise than one, and apart from this, you’ll also generally have lower top speeds and weaker pulling power from a geared hub motor than from a mid-drive motor. Ultimately, they’re an inoffensive pick that won’t break in a hurry and won’t weigh you down much either, making for a decent entry-level consumer choice.
Hub Motor Placement
The last element to consider in terms of motor types is the placement of a hub motor, regardless of whether it’s of the direct-drive or geared variety. This is a pretty simple choice to make, and the pros and cons of front and back wheel placement are easy to understand. A motor placed on the front wheel of your bike pulls the bike forwards, whereas a motor placed on the back wheel pushes it.
In terms of significant benefits, both placement choices have a few. Front-wheel motors can handle all types of gearing setups as they aren’t connected to the drivetrain. They’re also easy to install for the same reason and often work well as a counterbalance to a heavy rear battery. Back-wheel motors, meanwhile, have some benefits of their own. For one thing, they give you more rear-wheel control than a front-wheel hub. They’re also compatible with pedal assist via the drivetrain, thanks to their rear-wheel placement. On top of this, the increased structural integrity of the back of a bike allows for a higher power rating without worrying about a motor’s weight allowance.
There are also some drawbacks to each type of placement. A front motor, while a good counterbalance, can put too much weight on the nose of your bike, leading to a gyroscopic effect when cycling at high speeds. Front motors often have lower power ratings, too, as they require strong spokes and forks to accommodate their weight. Meanwhile, back motors are complicated to install and maintain due to their increased connectivity with the rest of the bike. Back wheel motors also place all of your drivepack’s weight at the rear of your bike, meaning hill-control and acceleration both suffer a little.
What Do The Power Ratings of Ebike motors Mean?
Wattage vs. Torque
When you’re reading up on electric bike power specifications, it can often be hard to tell what exactly a motor’s wattage or torque potential translates to in the real world. Some people don’t know that the statistics are essentially useless on their own – you need to look at both torque and wattage to understand the power of a motor. This is because they are directly related; in essence, power (wattage) = torque over time, with torque being the pushing/pulling power delivered to the wheel of your bike via your motor.
In basic terms, the higher your torque, the easier it is to pedal your bike on any given surface or slope. Higher wattages generally increase your torque at varying efficiency rates, depending on the rest of your motor’s specs. The important thing to note is that torque defines how hard a wheel is spinning rather than how fast. High torque motors are always better for rapid acceleration, load-bearing, and hill climbs but often have a slower top speed than low-torque motors of the same wattage. Meanwhile, a low-torque motor on the same wattage does the opposite; it accelerates slower than a high-torque motor but continually applies force at higher speeds.
Therefore, as a rule of thumb, a 500W motor with low torque will more easily maintain a high top speed than a 500W motor with high torque. Conversely, the high-torque 500W motor will excel at load-bearing, hill climbs, and acceleration from stops but apply less power at top speed.
Common Wattage Levels
With all of these complicated stats in mind, you may be left asking yourself, well, just which electric bike motor do I need? As noted, while wattage on its own is not the most useful metric, it can help in this scenario by giving you a general idea of a motor’s abilities. Higher wattage almost always means your bike can achieve more, both in terms of speed and load-bearing – especially in terms of the latter, as the higher a mass your bike or cargo has, the more power you’ll need to reach a high torque.
Let’s look at common electric bike motor wattages and what kind of riders they’re each suited to. To begin with, you’ll see a lot of bikes reporting a 250W motor, which in some states and countries is the maximum allowance for an electric bike before it qualifies as a motorbike or moped. ‘250W’ on its own doesn’t mean all that much, but in general, these bikes aim to provide as much power when engaged as a ‘regular’ cyclist would when pedalling. These motors have a long battery life, they’re lightweight, and they’re good for people looking to get back into exercising, giving you a bit of an added boost for hills and long journeys.
A 500W motor is a nice mid-range, mid-weight pick that gives you some real power to take on steep hills and provide high torque for carrying cargo and improved acceleration. It’s something of a middle-of-the-road option, as a 750W motor will elevate you into fast commuting and performance bike territory. A 750W motor essentially turns your bike into a quasi-road vehicle, providing a lot of speed but often on shorter battery life than lower-wattage motors. In general, 500W and 750W motors are ideal for frequent commuters performing daily short trips and charging their bikes each evening.
Beyond this, you’ve got 1000W motors and above. Equipping your Ebike with a 1000W motor brings it closer to a moped than a pushbike. Once again, 1000W Ebikes are good commuter options, and some use this power to reach extremely high speeds. Something to consider is that 1000W motors are real battery-drainers and often much heavier than similar lower-wattage motors, making them an inconvenient choice for performance-focused riders. They’re more of a specialist pick for very specific riding conditions or DIY-builders looking to soup up their builds.
While there is a massive range of Ebike motor brands out there, you’ll see a few cropping up time and time again. To begin with, in terms of pre-built bikes, you’ll be seeing a whole lot of Shimano STEPS motors and Bosch options on offer. These two are both very reputable brands with years of history, Shimano having specialized in bike manufacturing and Bosch in electric consumer tech of all kinds.
Shimano’s famous STEPS motors are a range of mid-drive options available in various builds, including city, trekking, mountain biking, and cargo configurations. They often have long-range batteries, and all come equipped with sophisticated cycling computers to allow for true pedal-assist sensor systems. Even though they’re mid-drive motors, they’re remarkably durable, as they’ve been developed specifically to reduce wear and tear on the crankset, shifters, and chain.
Bosch’s motors are also fantastic consumer-level options. Their range includes City, Overland, Touring, and Mountain biking options, all of which fall into Active, Cargo, or Performance-specific lines. Their Cargo and Performance lines are focused on maximizing torque, while their Active motors are built around riding on flat surfaces with infrequent stops.
For those seeking an activity-specific motor, SportDrive is another great brand to keep an eye out for. They specialize in mid-drive motors built for performance with high torque ratings, making them good picks in terms of acceleration and hill-climbing. These motors are built to be quiet and stealthy, and they’re perfect for both commuting and countryside rides.
Last but not least, for DIY enthusiasts building or tweaking their Ebikes, Promovec is a brilliant one-stop shop.
These guys sell a wide range of motors as individual components, including lightweight front-wheel hub motors with low torque setups, mid-drive torque-heavy picks for performance riding, and rear hub motors with a more balanced overall performance profile. Promovec even sells full E-kits to make DIY setup easy, with a range of Entry-level, Premium, Design, Cargo, and Foldable options – all of which include motors and all the other parts you’ll need to get them going.