Which Motor Suits Best?

Firstly there are geared and gearless motors. A geared motor does not have a gear change mechanism it simply means the motor in the hub goes through a set of gears (usually planetary gears located inside the hub) to drive the bicycle wheel. The gear reduction ratio depends on the motor design . A gearless motor has no gears and the rpm of the bike wheel is the same as the rpm of the motor inside the hub eg all crystalyte motors and the GL series of motors.

A very general  short answer is this:

If you have no hills or very minor hills a gearless motor is most definitely the way to go.

If you have steep hills then a geared type motor maybe be more suitable.

You may have a combination of both which is more likely going to be the case, some hills and some flat road. Then its harder to decide which is the best type of motor. For me I personally don't like going over about 30km/hr, I'm quite happy to sit on 20 to 25km/hr so in my situation a geared motor will do the job as I dont need a high top speed. If I have some hills to tackle then the geared motor will give very good assist on hills even at slow speeds.

A gearless motor on the other hand, if you are in a situation where the hill is steep enough that you really have to pedal hard and you can only go up slowly, will not be the best solution. The reason being this: in a gearless motor the slower you go the less efficiently the motor operates, so if you are going up a steep hill and the going is slow then a gearless motor will be running very inefficiently because its rpm is low, it wont assist an awful lot (will die on hills) and will waste alot of battery energy. For the same slow speed of a bike up a steep hill a geared motor can still be running at an rpm that is efficient for the motor. You can think of it like this: a gearless motor going up a steep hill slowly under load is like trying to go up a steep hill in a car in top gear.

If you are the type of rider who can offer some pedal assist on hills and keep the bike speed up then a gearless motor may still be ok for medium steepness hills. If you have no hills at all then your in a very fortunate position as a gearless motor will be suitable and pedalling will not be necessary at all (unless the batteries are flat!)

Generally geared motors have a lower top speed compared to gearless motors ( exception being the bmc geared motor). Geared motors top speeds range from about 20km/hr up to about 40km/hr depending on voltage of motor and some other factors.

Gearless motors top speeds are higher being about 40km/hr for a 48volt motor (just as a rough idea of speeds).

One other important factor is the type of batteries used: if using lithium batteries which are quite light weight then a gearless motor is quite ok on steeper hills,
but if using sealed lead acid batteries then a gearless motor is going to loose power on steeper hills and chew up the amps.

For very steep hill climbing its hard to beat a chain drive system running via the rear gears, though they do tend to wear out sprockets and chains very quickly.

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