Electric Bike Conversion Kits

electric bike conversion kit

This is a beginner’s guide aimed at those with limited knowledge of the subject and I have tried where possible to avoid jargon.

In this guide I don’t promote any particular system or brand, the aim is just to give an awareness of the options available and a basic explanation of how they function.
I should also clarify that this is aimed mainly at a UK audience, as rules and regulations vary around the world. What is legal in one country or region is illegal in another and I am not going to attempt to explain the legal aspects here as this subject is well documented elsewhere.

Having arrived at this section of the Pedelec’s site, I’m sure you are already curious about electric bikes and might be wondering what the benefits of investing in a conversion kit might be, in comparison to buying an ‘off the peg’ complete electric bike. The good news is you are in the right place and whichever option for ‘going electric’ you decide to go for there is expert, impartial advice available both in these guides and on the pedelecs forum (including directly from trade members).

OK, let’s talk about some of the benefits. Over 90% of non-electric pedal cycles and tricycles can be converted with one system or another, so a bike you already own, the one that has been sitting at the back of a shed for years or one that you use regularly, can in most cases be the basis for electrically assisted cycling. And something really important to point out about kits is that if at some time in the future you decide to change your bike, it can be removed and fitted to another bike. Alternatively, you may be thinking of buying a new or used bike with the intention of converting it yourself or having it converted for you.

Types of kit available

There are currently 3 types available:

  • Hub motor
  • Crank motor or centre drive
  • Vivax Assist formerly know as Gruber Assist

The most common and readily available kits have hub motors that can be either geared with a set of internal planetary reduction gears that drive the hub mechanically, or direct drive, which takes the power coming from a motor without the use of reduction gears.

These types of kits normally come with the motor already built into a front or rear wheel replacing the existing wheel. They are available in a range of sizes, commonly 20”, 26” and 700c or 28”.

One important thing to check before choosing a kit is will the forks accommodate the motor wheel? The crucial measurement is the width of the ‘dropouts’, that is the distance between the front or rear forks where the axle locates. Forks made from aluminum or steel can be spread or pulled closer together to a degree to fit the hub motor axle and there are acceptable tolerances of between +/- 5mm for this measurement. If there is a larger discrepancy, please seek expert advice. Although it has been done, for strength and safety considerations, I do not recommend fitting a kit to a bike with carbon fibre forks.

Front or rear wheel drive?

Firstly, it is only possible to have front wheel drive with a hub of direct drive motor, this is not an option for crank or Vivax systems.

The choice of a front or rear kit is a subjective matter, but there are some issues to consider. If the bike is normally to be ridden on roads and paved cycle tracks then a front motor is probably the better choice, especially if the battery is rear mounted as this arrangement gives better weight distribution between the front and rear of the bike, it is also easier to install as you do not have to make any changes to the existing gears. Another plus point is that you have in effect 2 wheel drive i.e. a human powered rear wheel and a motorised front wheel.

There are some things that people may not like about front hub motors, the steering is going to be heavier to a small degree and if you are spending a lot of time riding ‘off road’ on loose and slippery surfaces, a rear motor may be a better choice as far as traction is concerned as you have more weight over the motorised wheel. If you decide on a rear hub motor conversion, you will have to change the gears. Please note that you cannot use this type of conversion on a bike with hub gears, e.g. Shimano Nexus etc.

With derailleur gears, this means fitting a ‘screw on’ freewheel to the motor hub with the same number of sprockets as your existing setup, however some rear motors are available with the same splined shaft your existing derailleur cassette uses.

The crank drive types of motor that are available for conversions drives through the bike’s gears via the chain and is mounted to the ‘bottom bracket’ shell, (this is the part that connects the crank arms and pedals together and rotates through a bearing mounted spindle). There are fewer choices available with this type of kit, but it does have an advantage in that an existing bike wheel does not need to be changed and as is the case with a front hub motor neither do the gears.

Finally Vivax Assist; this is a unique system most of which is concealed within the frame of bike, a compact electric motor is fitted inside the seat tube and drives the bottom bracket through bevel gears. Currently, there is only one manufacturer offering this type of kit. Like crank drive, it has the advantage that an existing bike wheel does not need to be changed and as is the case with a front hub motor neither do the gears.

In some cases the conversion kits are manufactured by companies that also make complete electric bikes and share a lot of the same components.

Battery Power

At the time of writing the vast majority of batteries supplied with conversion kits have Lithium Ion cells, the same as you will find in mobile phones and many other devices but with a much larger capacity.

Kits are readily available with 24, 36 and 48 volt batteries and capacities from 8 to 20 Ah or amp-hours. The higher the voltage the greater the power of the motor and the higher the capacity the greater the range.  The battery may be located on or within a rear rack which can also be used to carry luggage, on the down tube where a water bottle would normally be found or in the case of some folding bikes in a soft bag attached to the handlebars.

A compatible battery charger will also be supplied that is powered from a normal domestic 13amp plug socket.  Some manufacturers can also supply a DC/DC charger that is powered by 12v supply from a motor vehicle. This is useful for people with motorhomes etc., who have no access to a domestic supply.

The Controller

This is the brain of the system. It connects all the electrical components to each other and regulates the delivery of power to the motor. It may be a separate ‘black box’ which is fitted to the frame, on the rear carrier or in some cases integrated in to the motor.

Handlebar Display

Most kits have a handle bar LED or LCD display with varying degrees of sophistication, but basically it allows you to set the desired level of power and mode of assistance and will also show the remaining capacity of the battery.

Pedelec or e-bike mode

Most kits will have a pedelec sensor that detects the rotation of the crank as you pedal or senses the level of pressure applied to the pedals, this in turn activates the delivery of power to the motor. With the pedelec system, you must pedal. In addition several kits have a throttle that can be in the form of a twist grip like a motorcycle, a thumb throttle or simple button that is pushed when a boost of power is required. The throttle can be useful to have in traffic when you need instant power assistance. The twist grip and thumb throttle allows variable power assistance without having to pedal, however using the throttle without pedaling will drastically reduce the distance that you can ride.

Brake Levers

Most kits include a set of brake levers with electrical cut offs that stop the power going to the motor as soon as pressure is applied to the levers. Alternatively, there may be a cut off supplied that attaches to the existing brake levers. The brake levers supplied as standard with kits are cable operated, so they can’t replace hydraulic brake levers or those combined that are combined in one unit with the gear change.


In the majority of cases, a wiring loom connects all components with connectors that plug into each other. The best systems will have weatherproof connectors that cannot be wrongly connected.

DIY or Professional Installation?

A good kit will be supplied with a set of instructions that explain each stage of the installation process that should be adequate for someone who is familiar with basic bicycle maintenance and has reasonable level of DIY skills. You can always ask for the instructions so that you can see what is involved before you decide to buy.
However, if you feel daunted by the whole prospect, you can have the conversion completed by a professional, be that the supplier or a local bike shop. If choosing the latter option, it is good idea to take the installation instructions with you to the bike shop first and ask them to quote for doing the work.

A third way: there are some expert members of the Pedelecs forum who have previous experience and may volunteer to help you.

Buy Locally or Import?

It is possible to import a kit yourself and save on UK prices, but you need to factor in that you will almost certainly have to pay import duty and VAT when it arrives in the UK, so the savings may not be so great as they first appear. Also you will not have the level of support and backup you can expect if you buy locally.

How Much Will It Cost?

At the time of writing, a new conversion kit is going to cost from a few hundred pounds up to almost £2000 in the UK, depending on the quality and degree of sophistication, but a perfectly good kits are available for £1000 or less. This may sound like an expensive outlay, but you will almost certainly use your bike more, spend less on fossil fuels, parking fees and public transport. You will also be doing your bit for the environment and in the long run can recoup your investment.

John Douglas, Cyclezee

July 2013


Want to find out more about conversion kits? Join in the chat on Conversion Kits on the Pedelecs forum here.