Best Electric Bike Motor: Bursting thru 250W
At first glance, motors for electric bikes might seem interchangeable. After all, all of them are rated at the same power – 250 Watts.
The reality, however, is much more complex. Different motors do operate at different power levels and some are better than others.
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Aren't all Ebike Motors Limited to 250W ?
UK Law requires that electric bike motors provide no more than 250 Watts of "continuous" power. Fortunately for owners of ebikes, “continuous power” is poorly defined. As a result, most manufacturers can legitimately say that their motor is 250W, when in most situations their motors operate at substantially higher power levels
Remember that if any manufacturer claimed that their motor could operate “continuously” at higher power levels, it would be disqualified from sale in the UK.
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The argument has also been made that ebike motors are overspec'd so as to minimise the risk of any motor requiring repair during the warranty period.
To support the above I attach a chart leaked by Bosch in 2017 comparing their ebike motors to their competitors'.
Disclaimer: This chart is old, and reliable sources say that it is inaccurate. The point of its inclusion is to show that 250W is not a hard ceiling.
Source: https://electricbikereview.com/forums/threads/ebike-motor-power-curve-comparison-chart-bosch-yamaha-shimano-brose.14085/
As you can see, in 2017, the main 250W motors were generating between 400W and 550W of power for a typical cyclist, pedaling at between 60 and 80 rpm.
This chart shows just raw power. Technology has advanced a lot since 2017. So, even if peak power itself has not increased since then, the effectiveness of how that power is used will have advanced considerably.
Is Torque a Better Measure of Power?
A nerd would tell you that torque and power are different things. Although true, often torque is what people mean when they say that a motor is “powerful”. Specifically, torque is what makes a bike accelerate quickly and able to climb hills with ease.
There are no legal limits on the torque of ebike motor, and so these figures tend to be more accurate. However, as with all things technical, there are complexities. Namely, electric bike manufacturers tune their motors for particular riding styles and conditions.
The above graph shows power output at various rates of pedaling. In 2017, Yamaha chose to provide peak power at around 70 rpms … which is closer to how fast a novice cyclist pedals. Bosch chose to peak around 85 rpms, and Shimano around 95 rpms.
In June 2020 Bosch released a software update that increased the torque of their Performance Line CX Gen 4 system. If torque were a fixed characteristic of the motor itself, a software update wouldn't affect it.
Nonetheless, if you want a single number to give you a rough sense, then torque is a good starting point for comparing the “power” of different ebike motors.
Mid-drive vs Rear Hub Motors
Electric motors produce torque. Torque from the motor then needs to be transferred to the wheels.
A separate article discusses why you should get a mid-drive motor for your ebike. Below, I will explain the difference in terms of motor characteristics.
Hub motors transfer power directly to the wheel. Rear hub motors transfer power directly to the rear wheel. Front hubs to the front wheel. The problem with this approach can be seen in the above graph.
Although the graph compares mid-drive motors, all motors like to spin at a pretty good clip. If a motor works too hard (and spins too slow), it burns out. If it spins too slow even when not working hard, it heats up. Running an electric motor slowly is inefficient.
Hub motors only have a single gearing. On the above graph for mid-drive motors, how fast you are pedalling determines where you are (horizontally) on the graph. With hub motors, how fast the bike is moving determines where you are on the graph. These are decidedly different things.
As a consequence, manufacturers of hub motors tune them for an optimal road speed. If the bike is moving slower than this, it is less efficient.
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Mid-drive motors tend to outperform hub motors because they use a bike's existing gears. If you are climbing a hill, you downshift. This allows both you and the motor to continue pedaling and spinning at a reasonable rate despite the extra effort required for the hill.
If you are on the flat, you upshift, allowing you to not have to pedal faster than you are comfortable with – and the motor to not spin faster than is most efficient.
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Johnny Nerd Out demonstrated the difference gearing makes on an identical bike with virtually identical motors from the same manufacturer.
The side by side demonstration starts at 03:21
CONCLUSION
Despite nearly all ebike motors being rated at 250W, they definitely are not the same.
For one, some motors are decidedly more powerful than others. In addition, different motors are tuned for different riding styles and conditions.
Our advice for finding the best electric bike for you takes into account both your riding style and riding conditions and includes a brief discussion of ebike motors that might be most suitable.