..this is from the Battery Vehicle Society website ;
Not all electric bikes are the same and if you’ve never tried an electric bike, here are a few pointers to help you identify which is the right bike for you.
Know the law
The law defines an electrical pedal assisted cycle (EAPC) as a pedal cycle with a small electric motor to assist the rider.
Maximum powered speed of the cycle is 15mph and the maximum motor power is 200w continuous output (250w for a tricycle).
The maximum weight for the electric bicycle is 40kg (60kg for a tricycle) and this weight includes batteries.
In addition, an electric bicycle must conform to normal bicycle construction and use regulations.
Electric bicycles are regarded in law as a bicycle and not a motor vehicle. As such, any electric bicycle conforming to the above definition can be used without insurance, tax, MoT certificate or safety helmet. The only caveat is the rider must be 14 years old or over.
When you are buying an electric bike – especially if you are buying across the Internet – make sure the electric bicycle you are buying conforms to these regulations. A surprisingly large number of them do not and this could have serious repercussions for the owner: buy an electric bicycle that does not conform to the EAPC legislation, and you can be prosecuted for driving an un-roadworthy motor vehicle without tax, insurance, and MoT. Have an accident in an electric bicycle that does not conform to EAPC legislation and you face prosecution with a likely prison sentence at the end of it.
Power, power and more power
Electric bikes aren’t exactly the most powerful vehicles on the planet, but there is huge variance between different bikes available. By law, power output on an electric bike is limited to 200w, although voltage isn’t specified.
As a rough rule of thumb, higher voltages equate to more torque and better performance. That isn’t always the case though: electric motor performance varies considerably from manufacturer to manufacturer and some of the better designed bikes perform better on a 24v system than the cheaper bikes do with 36v electrics.
Most electric bikes have hub motors built into either the front or rear wheel. In general terms, rear wheel motors tend to be better, both for bike balance and also for low speed manoeuvring. In most instances, the hub motors themselves are single geared, so even if you can change gears on the bike itself, the gear change will only affect your pedalling, not the electric motor.
There are one or two exceptions to this rule, and the benefit of having a geared motor is improved hill climbing abilities. However, the difference tends to be slight, and for most owners this benefit is outweighed by the reduced ease of use.