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Thinking about converting your bike to electric, but don’t know where to start? In this Electric bike conversion kit guide, I will examine the different ways you can add electric assistance to your bicycle.
If you are willing to take the plunge, converting a bicycle to an electric assist can be an extremely rewarding experience. Not only that, but you can also make substantial savings when compared to buying a factory-produced e-bike.
Please note: The author of this electric bike conversion kit guide has 6 years of experience in this field and has converted 100s of bikes to electric assist.
DIY E-Bike vs Factory E-Bike
A typical entry-level mid-drive electric bike will cost in the region of £1600 ($2000). The brand new DIY mid-drive e-bike below cost me less than £900 ($1160) to build (including the cost of the new donor bike).
As you can see there are substantial savings to be made by converting a decent spec new bike to electric assist. If you are converting a bicycle you already own then the savings are even greater.
Let’s say you have an old Trek or Cannondale mountain bike sitting in the shed. Typically, a decent mid-drive conversion kit with a battery will set you back around £600 ($780). That’s a massive saving when compared with buying a factory-built mid-drive electric bike.
Converting a bike to electric isn’t for everyone though, and if you’re not mechanically minded, I would recommend purchasing a factory-produced electric bike or finding someone who can fit the kit for you.
You will also need to consider the fact that a retrofit electric bike conversion motor may not be as reliable in the long term as a Bosch or Shimano steps motor commonly found on factory-produced electric bikes.
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- Guide to converting your road bike to electric
To choose the right motor for your needs, you need to ask yourself what your intended use is going to be.
If you live in a fairly flat area, with only slight inclines, then a small geared hub motor should be more than adequate, but if you live in an area where there are relentless steep hills, then a mid-drive would be more suitable.
Ultimately, the decision you make will be influenced by your own needs. Both types of motors have their place on e-bikes but it is worth remembering that mid-drives in general are far more energy efficient than small hub motors.
Direct drive hub motors
The direct drive hub motor is the simplest form of electric bike propulsion: The outer shell of the hub is an integral part of the motor and has a big ring of powerful magnets fixed to it.
When the motor runs, it drives the wheel directly (that’s where the name comes from). Put simply this means that the wheel is a motor with the shaft fixed in place so that the body of the motor (the outer hub shell, and thus your wheel) spins instead of the shaft.
It is a simple design, but comes at a cost – the motor needs to be quite big and heavy to produce enough power. A smaller motor spinning slowly wouldn’t produce enough torque, and the speed you want your wheel to turn is relatively slow, so the motor needs to be as big as possible to produce torque at low speeds.
On the positive side, direct-drive hub motors tend to be cheap and reliable plus they can handle a lot of power. So if you are looking for a high-performance electric bike on a budget then a big hub motor may be the way to go.
Geared Hub Motor
Small geared hub motors are a lot more efficient than direct drive motors. The motor case is connected to the stator through a planetary gear reduction system. For every rotation of the case, the motor inside spins many times faster. This allows the motor to work at higher (and more efficient) speeds, while still allowing the wheel to spin at a slower driving speed.
Another great benefit to using a geared hub motor is there is practically zero pedalling resistance if the motor is switched off or runs out of power – you can pedal like on a normal bicycle.
Geared motors are usually maintenance-free, but if you do a lot of hill climbing it is likely the nylon planetary gears will wear over time. Thankfully these are cheap and relatively easy to replace.
Front Hub Motor vs Rear Hub Motor
Front-wheel Electric bike conversion Kit
There are various pros and cons of fitting a front hub motor vs a rear hub motor. When it comes to electric wheels, front hub motors are usually more straightforward to fit. The main reason for this is you do not need to worry about swapping over gear cassettes or freewheels.
It should be noted, that the best option for a front-wheel electric conversion would be a small, geared hub motor. The reason for this, is they are compact, lightweight and produce reasonable torque.
Larger direct-drive front-wheel electric bike kits are available. They are generally cheaper and more powerful, but the extra size of the motor can make it difficult to fit onto bikes that have disc brakes. They are also considerably heavier and less efficient.
Another plus with a front hub motor is when you are using the pedal assist, the bike is effectively being driven by both wheels. Whilst the electric front wheel is giving you help, you are putting power through the rear wheel by pedalling.
Electric front wheels are not particularly good for off-road riding, as the powered wheel can tend to spin on rough ground, particularly when climbing steep hills.
Rear Wheel Electric Bike Conversion Kit
A rear-wheel electric hub motor is usually the preferred way to add electric assist to a bicycle using a conversion kit. Changing the rear wheel involves a little more work, specifically removing the gear cassette (or freewheel), you will need a special tool for this job.
As far as riding is concerned, the motor is pushing as opposed to pulling you (as with a front motor). Generally, a smaller geared rear hub motor will look a lot more discreet.
Another bonus with rear hub motors, is they are a lot better for use on rough ground. All of the rider weight is concentrated on the back wheel, there is much less of a problem with wheel spin.
The only real downside with this setup is replacing an inner tube in the event of a puncture can be time-consuming. I always recommend a good puncture-resistant tyre like a Schwalbe Marathon Plus to greatly reduce this risk.
The mid-drive motor is the preferred drive system of more expensive e-bikes. These types of motors are by far the most efficient and they also produce much more torque than hub motors.
Fitting this kind of motor can be tricky for the inexperienced, as the bicycle’s bottom bracket needs to be removed to facilitate installation. Once this job has been done, the rest is fairly straightforward. It is important to remember that most mid-drive kits are only compatible with standard threaded bottom bracket shells 68 mm-73 mm wide and approximately 33.5mm in diameter.
When installed correctly, a mid-drive system will give your bike the look and feel of a more expensive e-bike.
The only downsides to mid-drive motors are increased pedalling resistance when the motor is switched off and periodic maintenance (such as tightening the motor). You will also be limited to a single chainring on the front.
Mid-Drive vs Hub motor
Taking into account all of the above information it boils down to your budget and the kind of riding you plan on doing.
In my experience, small hub motors are usually a lot less hassle than mid-drives in the long term. Another thing to consider is pedalling resistance. Both the mid-drive and direct-drive hub motors produce a significant amount of resistance with the motor off.
Mid-drives are much better at hill climbing, a 250w Bafang BBS01B will produce nearly 100% more torque than a geared hub motor equivalent.
Hub motor kits have more of a ‘DIY look’ about them, there will be an external controller (usually in a frame bag), an external pedal assist sensor and lots of wiring to tidy up. Mid-drive motors definitely provide a cleaner and neater-looking finished product.
Choosing the Right Battery
Battery choice is important because it will determine the kind of range you can expect from your electric bike.
First and foremost you will need a battery of the right voltage. Most kits are 36v or 48v, the 48v kits will usually take 52v batteries but this can in some cases compromise reliability. There are some motor controllers available that will take either a 36v or 48v battery but you will need to double-check this first before making your purchase.
The Ah (amp hour) spec provides a measurement of battery capacity. In other words, it is an indication of how much energy can be stored by the battery. For example, a 36v 13ah battery (36v x 13ah) will have a total energy capacity of 468Wh (watt hours) – using a constant 20Wh per mile would give a range of approximately 23 miles. In real-world riding, this figure could be much greater or lower depending on the power level used, rider weight, the kind of terrain (flat or hilly) and wind direction.
The other thing to consider is the size/style of frame you will be fitting the battery. Normal hybrid or hardtail mountain bikes of 18″ frame and above usually have plenty of space, but when you get down to 16″ frames, things can become a lot tighter.
If you have a full-suspension mountain bike then mounting a battery in the frame can be practically impossible (depending on the bike). Ladies framed bikes and step-through bikes are usually better suited to a rear rack-mounted battery.
You should take measurements of your frame triangle before purchasing a battery. It is also worth noting that some battery packs do not align particularly well with the bottle holder threads on the frame. If this is the case, you may need to drill and riv-nut an extra hole or two.
For more information on e-bike batteries please check out my article ‘electric bike batteries explained’
If you are looking for a bit of help with hills but want to pedal under your own steam for a lot of the time, then a small geared hub motor would be the way to go. If you are looking for a bike that will be able to tackle very steep climbs with ease, then maybe a mid-drive would be a better option. Either way, converting a bike to electric can be both challenging and rewarding.
Most people don’t choose to convert a bike because it’s the ‘easy option’. But, they’re looking for something unique to them. Or, they have an old bike with sentimental value. If you’re up for the challenge, then I’d say give it a go! But, please remember to check the e-bike laws in your country of residence.
Thank you for taking the time to read this article, and we hope you have found this electric bike conversion kit guide useful. If you need any further help or advice on choosing a conversion kit, please leave a comment below.