There are many different kinds of ebike motors. What differentiates them is mainly their position on the bike, and their power.
The position of the motor on the ebike
The motor of an ebike can be positioned on the hub (the central point of the wheel), or between the pedals.
Front hub motors: They are the simplest and least expensive kind, and therefore many ebike conversion kits are based on this kind of motor. They are very easy to install because they do not interfere with the pedals or the transmission. However, they have some down sides: they are the least efficient in case of a slippery surface (such as wet asphalt, dirt roads) or uphill, because the front wheel may spin. Moreover, they augment the load on the front fork, which – in case you install a front motor on a bike which was not originally designed to host one – we suggest you change with a bulkier product. We advise you to choose these kinds of motors only if you think you will use your ebike on simple and mostly flat routes.
Rear hub motors: With this kinds of motors you can avoid the risk of having the wheel spin on a slippery surface, because most of the weight of the rider is on the rear wheel. They are generally a bit harder to install on a regular bike, as their position interferes with the derailleur.
Mid-drive motors: these motors are installed in a central position on the bike, between the pedals, and they act directly on the transmission system of the ebike. They are more complicated to install, and often they require a purpose-built frame, but they do not interefere with the wheels, which comes in handsome when you have a puncture. Because they are attached to the frame, and they are not positioned on a suspended mass such as the wheel, they do not fear hitting potholes, and they are therefore a must on electric mountain bikes.
There is also a difference which concerns how the rotation speed of the ebike motor. The rotation speed of hub motors is determined by the rotation speed of the wheel; this means that when the bike moves slowly (for instance when you start off, or when on a steep uphill sector), the motor has to deliver its power at a low rotation speed, in an inefficient way, absorbing a lot of energy from the battery. Mid-drive motors instead, because they act directly on the transmission, can always work at an optimal rotation speed – provided the cyclist selects the right gear – and therefore consume less battery juice.
In general – but there are exceptions – mid-drive motors use torque sensors, which determine the effort put by the cyclist, and therefore ensure a more natural cycling mode. Hub motors instead – again, with exceptions – are coupled to simple cadence sensors, which provide for a less natural feeling but which, on the other hand, allow the cyclist to use what we call the “symbolic pedalling” mode (please refer to our page on ebike pedalling sensors for a longer explanation of the differences between the two types of sensors). E-cyclists debate passionately – and sometimes even angrily – about which kind of motor is “better” than the other. The generic advice which we feel we can give is as follows: if you have a low budget, you know that you won’t use your ebike on very long or very steep routes, and you are interested in the “symbolic pedalling”, then go for a front or rear hub motor. If instead you have a higher budget, you want to go far and high on your ebike, and you don’t need the symbolic pedalling, then it would be better to choose a mid-drive motor.
The market seems to be moving towards mid-drive motors anyway, as most big manufacturers prefer this solution for their high-quality bikes.
The power of the ebike motor
Another important factor to take into consideration is the power of the motor. Most ebike motors have a nominal power between 250 and 850 Watts. The more power your motor can deliver, the faster you can go (especially uphill); on the other hand, the motor will be somewhat heavier, and it will also consume more energy, requiring a bigger, heavier and more expensive battery.
A lot depends on the law in your country. In Europe for instance the motor of an ebike can deliver at most 250 Watts; it is possible to install more powerful motors, but then the ebike is considered by the law just like any other motorcycle, requiring insurance, the use of an helmet, and more red tape; if you want your ebike to be classified like a normal bicycle, in Europe it has to have a motor of 250 Watts or less. Something similar exists in most countries; please refer to our page on ebike laws for more information.
The European example can be useful to clarify this issue. Most people in Europe are pretty happy with their low-power 250W ebikes, and wouldn’t want or need anything more powerful. However, with these motors when you ride on a steep ascent you really have to “help” the motor by pedalling intensely. If you plan to use your ebike on a route with many, long and steep uphill sections, you may want a more powerful motor to help you along. However, be aware of what we have written above about needing a bigger battery. It’s a trade-off, and you have to decide for yourself what it is that you need. Our advice is to try or rent as many ebikes as you can before investing in one, so that you can test them on a typical route you’ll want to ride on.
The quality of the ebike motor
Once you have established the kind of motor that you need for your ebike, there is really not much to decide. Ebike motors are not a very complicated technology, and unless you go for something suspiciously cheap, you shouldn’t experience any problems concerning realiabilty, at least for a standard usage.
Until a few years ago, the market for ebike motors used to be divided between brushless and brushed motors; without delving too deep into technical issues, a brushless motor is lighter, smaller, more efficient, and more reliable. Nowadays serious manufacturers offer brushless motors only, and if you are offered an ebike with a brushed motor, we suggest you to avoid it.
Once you know where you want your ebike to have its motor (hub motor or mid-drive motor) and how powerful it should be, the real difference between ebikes is made by the quality of the pedalling sensor and that of the battery, and by the quality of the mechanical components of course.