As with every other question about a new electric bike, the answer to this one comes down to your personal needs and choice. Will your daily commute take you off road, and over the top of a mountain? If so, you are going to need the kind of big, tough motor that is found on, for example, Optibikes. Their top of the line mountain bike is powered by a 48 V lithium ion battery with a Cool CarbonTM 1100 W Motorized Bottom BracketTM. With this, you could commute over mountains without much trouble. And in fact, many people do! On the other hand, if your commute is more conservative, your needs will be similarly less conservative.What Size Electric Bike Motor Do You NEED for Your Electric Bike
Like Optibikes, BionX offers a whole range of motor sizes, so you can choose something that meets your needs. You can even buy a kit to convert your existing bike for a very reasonable price (especially considering that they make premium quality products). Their Premium series pairs their SL 350 HT DT XL motor with an extra long-range 48 V battery, and claims a range of 105 km (65 miles). This bike has a 350 W motor (Bionx is one of my favorite premium electric bikes kits, and are reviewed here).
At the other end of the range, the BionX PL 250 M is a much smaller motor, at 250 W. However, I used one of these for years, and it easily sufficed for my needs (my Bionx PL 250 is reviewed here). At the time, I was not doing any hills, and just needed a boost so that my long commute would be faster and less daunting. I upgraded to one of their 350 W motors when my commute changed to include a couple of long, steep hills. (Bear in mind that I weighed just under 200 pounds for most of this time.)
Minimum Electric Bike Motor Size for Your Electric Bike
In a nutshell, you should not be looking at a motor smaller than 250 W if you have to deal with hills. And if you weigh more than 200 pounds, your minimum should be 350 W. Unless you are riding a bike such as the BH Emotion Race Bike, which cleverly combines gear power with a crank-drive 250 W motor. With this bike, I can climb major hills without too much sweat.
Another example is the Haibike Xduro Trekking, which has a crank drive 350 W motor, combined with 27 gears. With this bike, you can do very long, tough climbs. Of course, you have to help out with some vigorous pedaling. But as you ascend the hill you can gear down further and further, and you can really feel how it assists you more with each gear change. With the result that a 350 W motor is enough for long and hilly commutes (assuming you are happy to contribute your strength and energy as well). You can read a full review of the Haibike Xduro here.
A 350 W motor will meet most needs, and will take a heavy cyclist up big hills with minimal sweat (but not without pedaling). After that, the bigger the motor, the more power you have. The 500 W motor is very powerful. The 750 W motor is tremendously powerful. The 1100 W offered by Optibikes is insanely powerful, but the price tag matches the power.
But bear in mind that the bigger the motor, the bigger the battery you need. So a powerful 500 W engine will need a big battery, making for a heavy combination. On the other hand, the beautiful Swiss-made Stromer electric bikes are big and heavy – but fast and wonderful.
Also, bear in mind that none of these sizes gives you a motor scooter. All the way up to 750 W, you still have to do some pedaling. But that’s a good thing. If you didn’t want to pedal and get fit, presumably you’d be reading a post about motorcycles.
Size Doesn’t Matter with Electric Bike Motor Sizes
Well OK, size matters a bit. But the point is that configuration comes into it too. For example, if you ride an awesomely engineered Emotion Race Bike (reviewed here), the excellent Panasonic motor is in the crank drive, so that the motor and gears work together to give you amazing speed and hill climbing ability.
You will ride fast on an electric bike, so please do it safely. I highly recommend a Mirrorcycle as a safety feature. It is cheap, but it makes cycling SO much safer. In fact, I recommend a rear view mirror as an essential safety device for all cyclists. You wouldn’t drive without one, so why cycle without one?
Laws about Electric Bike Motor Sizes
Finally, keep in mind that there are laws about the size of motor that electric bikes can have. In the EU, Japan, China, and other countries, the power limit is 250 watts. In Canada, 350-watt engines are common. Eight of Canada’s provinces allow electric power assisted bicycles, and in seven of these, they are limited to 500 watts output. In the province of Alberta the limit is 750 watts. In the USA, the limit is 750 watts. In the UK cyclists are severely limited, and the motor’s maximum continuous rated power output must not exceed 200 W for bicycles, 250 W for bicycle tandems (i.e. two seaters) and 250 W for tricycles. I am completely confident that this will change over time.
Usually you will not be able to buy motors that are too big for the laws of your own country (although with internet orders, it is possible to get around this). Also, highly technical people can put together motors that exceed legislative limits.
If you are not sure what is legal in your jurisdiction, get some advice from a reputable dealer.
We buy all our electric bikes at the same store, so we can be sure of continuous support from a reputable store (Evolution Bikes in North Vancouver).
You may also be interested in my post about Types of Electric Motors for Electric Bikes.