Which motor is the most powerful? Motor power is usually rated in "nominal" watts - but this does not tell the whole story. Keep in mind eBikes are not motorcycles, and if they were, the stats would say bike path legal eBikes are very anemic compared to even a basic gasoline motorbike. eBiking is about having a natural, sporty bicycle experience, in many cases, on bike paths away from motor vehicles. You can define your experience how you like - for us Its more about going farther, faster and arriving fresher - about feeling that biking exhilaration without worrying if your legs have got enough juice for the entire ride. A good eBike doesn't replace your power, it multiplies it. Stats can't tell you what you will feel on an eBike- for that you will need a test ride.
Nominal Watts vs Peak Watts - any given motor's technical metrics can create a lot of confusion because, well - they are very confusing, even to experts. Theoretically the power can be measured in peak watts or torque that a motor puts out - but many companies don't even publish peak watts, in many cases published numbers don't prove out in practice. If you are confused, that is a sign you are starting to understand how it all actually works in more detail. We have done a shootout between all the motor systems that can tell you which are the fastest steep hill climbers - but if you want to understand why, here is a breakdown of nerdy terms that frequently get talked about and what they mean:
Watts are a unit of measurement of power (or the rate of work) in universal terms, for electricity, or any machine or animal, including humans. James Watt was one of the early developers of the steam engine.
Mechanical Watts. When an object's velocity is held constant at one meter per second against a constant opposing force of one newton (1 Nm or Newton Meter), the rate at which work is done is 1 watt. For example, one horse power (or the amount of continuous mechanical power) delivered by one average horse is 750 mechanical watts.
Electrical Watts are calculated differently than mechanical watts, it is Amps x Volts. Increasing either the amps or the volts will result in more energy. Common household voltage is 120 volts so a 120 watt lightbulb uses 1 amp of power. If the bulb uses twice as much, or 2 amps, the watts used by the bulb would be 240 watts.
Bicycle racers regular measure their mechanical watts using stationary trainers with dynamometers that measure the actual mechanical energy (also expressed in watts) delivered to the rear wheel. Let's use some acronyms in this article to distinguish where the same word is used for a very different derivation - rear wheel mechanical watts are wWatts. Electrical watts are eWatts.
A conditioned bicycle racer climbing a steep hill or breaking out from the pack can go to more than 1700 peak wWatts, but only for short sprints. It is very hard to maintain 1700 wWatts of output for very long with having a heart attack - so really a fair measurement of a rider's power output is the amount of power that can be pumped out continuously without bonking. Typically that is an max average of 100 wWatts for casual cyclists, 200 wWatts for fit cyclists, upwards of 400 wWatts for racers.
Motor watts vs rear wheel watts. You may have heard the term "brake horse power" as a rating for cars. This is the power, measured by a dynamometer, developed at the motor. This is how powerful the motor is, not the car. The car's power is measured by putting the whole car on a stationary dynamometer with rollers for more real world conditions that test the actual power delivered to the tires. The difference between the two measurements reveals the efficiency of the entire car's systems.
Electrical Watts = Amps x Volts. Mechanical work is not what eBike manufacturers are referring to when they talk about watts - they are talking about electrical watts used by the motor (or eWatts). These watts are not the amount delivered to the rear wheel (or wWatts) like we see with bike racers. It should be noted, an eBike motor's torque rating is the torque developed on the spindle of the motor, not even to the cranks, and not to the rear wheel. Lets call the motor torque rating mTorque.
Watt Hours & Battery Range Batteries are usually talked about in terms of "watt hours", although manufacturers typically rate batteries in "amp hours". A one amp hour battery is one that can produce 1 amp of power for an hour. Most eBikes are 36 volt, so a 14 amp hour battery produces 36 x 14 or 504 eWatt hours of power. If your eBike has a 250 eWatt hour motor, and it is run continuously at 250 eWatts, the battery will last you just over 2 hours. If you run it at 500 eWatts your battery will last an hour.
Peak electrical watts at the most basic level, is the number of eWatts used by an electric motor and can be calculated from the voltage (usually 36) supplied by a battery multiplied by the current flowing (or amps) from the battery to the motor via a motor controller. The maximum current possible is determined by the ebike’s controller, and is usually somewhere between 15-30 amps, presuming the battery's cells and management system allow for that much power to be delivered. So an eBike motor connected to a 36V battery, being supplied via a 15 amp controller could use power at 15 x 36 or 540 eWatts. So then a motor's real world power to the rear wheal can be measured by how many amps a controller allows? Not exactly, but it certainly is a factor, along with efficiency, internal motor gearing, software algorithms. However, a vehicle's power is also factored by overall power to weight ratio depending on the weight.
Nominal Watts vs Peak Watts So the same limitation on peak vs continuous power for humans apply to electric motors - they are rated "nominally" for how much power they can safely output without overheating. However, this can be subjectively determined, mostly to conform to EU regulations that require an eBIke with more than 250 nominal eWatts to be regulated like a motorcycle, which requires registration at the DMV, a drivers license, and a license plate. Typically the peak eWatt usage of the modern mid drive motor is between 400-600 watts, even if they are stamped with a 250 eWatt "nominal" rating.
Modes In the real world with varied terrain, nobody really continually uses xxx watts, so calculating your estimated range it about averaging watt usage. "Mode" selection is usually measured by how much it multiplies your input, limited of course by the peak wattage the motor is capable of. Typically it looks something like this: ECO: 50% TOUR: 120% SPORT: 190% TURBO: 275% - in this example if you are pedaling at 100 wWatts, in ECO mode it should give you roughly 50 more wWatts - in TURBO you will get 275 more wWatts.
Software. Motor (and battery) controllers use algorithms that take in sensor data optimize your power usage, in order to avoid overheating, and also to maximize your range. Motors are tuned differently to give a different riding experience - sporty ones apply the power rapidly if you choose to use the higher power levels - but that will also drain your battery very fast - or smooth and smart to get better range. Indeed much of the innovation and competition between the motor systems is not about the raw power of their motor systems, but how the brains of the system interpret sensor input to sensibly deliver power when you need or want it, while at the same time budgeting your power so that you get the best mileage.
Power to Weight ratio One horsepower (or the amount of power a typical horse outputs) is 750 watts, but that does not account for the power to weight ratio. Sure a horse can put out 750 wWatts, but it also weighs like 7+ times as much as humans. An eBike weighed down by a heavy motor and battery is going to have a serious handicap climbing hills. It will also handle like a tank. This is why it makes less sense to just increase your battery size (if you want more range) than it does to make your eBike more efficient.
Efficiency. Both humans and electric motors are most efficient at around 80-100 rpms (rotations per minute). Think about when you are in too high a gear starting from a stop - it is really hard to get going. So you have to use a lot of power just to get going. If you down shifted to a lower gear it would not be hard. Most motor systems have a variety of tricks to optimize rpms - usually using "planetary" gears inside the motor that allow the motor to spin faster than the cranks. This is not just about getting better range - an inefficient motor puts out too much heat, heat overload will shut a motor down. Note that the modern pedal bike has technically evolved to optimize the efficiency of human pedaling - so human wWatts still count towards bicycle speed more than eBike motor eWatts Mid-drive systems. Mid-drive system develop torque at the cranks where we also pedal, so that makes them the the closest mimic to human power, which is why they are considered the most efficient.
"Direct drive" motors (usually in the rear wheel) are an exception to the internal "planetary" gears - these motors are basically two huge magnets without an moving parts. Many of these heavy old style rear hub motors are rated at 700-1000 eWatts or more peak power. So would a 1000 eWatt direct drive motor be faster than a 500 peak eWatt mid drive? The answer is yes and no. Typically hub drive motors 2+ times heavier and are 30% less efficient than mid drives, especially in stop and go conditions. This is because direct drive motors behave like us when we started in the wrong (highest) gear from a dead stop - a slow slog off the start that uses a lot of our torque - and direct drives have no gears inside to help spin at a more efficient rate. Every electric motor produces the most torque at the slowest rpms - but low rpms are also when they are also the least efficient. So direct drive motors have more low speed torque (which feels powerful off the mark), but because of this start up inefficiency problem, they have to have bigger motors and larger batteries to have the same power over the whole speed range as a mid drive. Weights on direct drive bikes get ridiculous pretty quickly when trying to increase real world power because of this.
Torque - this should be the conclusive way to compare the effective power of a system, but unfortunately the mTorque developed is measured on a lab bench does not directly correlate to either cTorque or rear wheel torque. For example, Brose claims that it's motor puts out 90 newton meters of mTorque. Bosch's Performance CX motor is rated at 75 newton meters of mTorque. So the Brose motor will climb a hill faster? Not in real world testing. There is probably a factual basis of their claims based on bench testing in a laboratory somewhere, but it does not tell the whole story any more than nominal eWatts do. Part of the reason for this is that both mid drive motors and geared front hub motors have "planetary" gears inside the motor that reduce the raw power of the motor to usable power for the drivetrain.
Since mid-drive motors also have drivetrain gears, they are the best choice to have the most possible cTorque and the best efficiency (if you shift properly) of any of the drive systems. Running both the electrical and your human motor at 100 rpms peak efficiency, working together - well that is what can make it really feel like it's you, only faster. Having a reasonably sized battery (because of efficiency scale on mid drives) allows for an eBike that also handles like a normal bike, keeping the experience natural but still enhanced.