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How big a motor do I need in my Electric Bike?

How big does my electric motor have to be for my ebike?

Our other post talked about the various numbers that manufacturers put on their electric motors and the summary there was that you couldn’t really trust that number because there were many factors in play.

This is also true for how big your motor has to be. There are many factors in play.

The most obvious two are

  1. How big a load will the bike be carrying? – This is you, plus your bags or panniers, plus the bike itself including its battery.
  2. What type of riding will I be doing on what type of terrain? – This means you have to consider how hard you plan to ride the bike. Where you plan to ride it and what sort of performance you are expecting.

Obviously if you plan to ride flat out with the bike doing all the work going straight up the side of muddy hills all day, then you’ll need a big motor.

If you plan to let the bike assist you most of the time and are mostly on the road with the occasional hill and a reasonable load, then you won’t need anywhere near as big a motor.

In Australia there is a limit of 250Watts on the motors in electric bikes. This is not a very big motor, but you’ll find it is more than enough for most riders.

The 250 Watt limit is a bit silly though considering motor location makes a difference. A 250Watt hub motor will push you along better than a 250Watt centre crank motor so it is a bit of a loose rule that they don’t really bother to enforce as far as we can tell.

The absolute best way to tell what size motor you need in your bike is to turn up to an electric bike shop (like ours) and take a few bikes for a ride with a backpack on your back or a load tied to the rear rack. Get a feel for what different bikes do.

In general you’ll get a lot better push from a bike with a higher voltage system. So if you are a bigger person, consider 48V systems over the 36V systems. The higher voltage bikes may cost a little more, but you’ll get a much better ride feel out of them and the motor itself is under less stress when you are out and about. Just like having a bigger engine in a car.


The fact the motor is bigger won’t automatically translate to a shorter range either. Range is mainly determined by how much you ask the bike to do for you compared to what you are willing to do, ie how much boost you have set.

A bike with pedals is still a bike, not really a motorbike, so they operate best when you pedal with them.

A lot of our bikes only provide motor power when you pedal. These are called Pedal Assist bikes.

Some of ours not only offer assistance when you pedal, but they provide that assistance in proportion to how hard you pedal (they have a torque sensor in the rear). This means that as you get to a hill and start to pedal slightly harder, the bike will give you a bit more assistance. This means that on the flat the bike doesn’t give much at all and thus you get maximum range from the bike while having a fairly constant ride experience.

Feel free to make a comment or pop in to the shop for a ride.


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