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Electric Bike Conversion Kit Guide – What You Need to Know

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The Ultimate Guide to eBike Conversion Kits

Thinking about converting your bike to electric, but don’t know where to start? In this Electric bike conversion kit buyers guide I will examine the different ways you can add electric assist your bicycle.

If you are willing to take the plunge, converting a bicycle to electric assist can be an extremely rewarding experience. Not only that, but you can also make a substantial saving when compared to buying a factory produced e-bike.

DIY eBike vs Factory eBike

A typical entry-level mid-drive electric bike will cost in the region of £1600 ($2000). The brand new DIY mid-drive ebike below cost me less than £900 ($1160) to build (including the cost of the new donor bike).

diy electric bike

The donor bike I used in the above build is a Decathlon BTWIN Riverside 900, with a Tongsheng TSDZ2 mid-drive motor and 36v 13ah battery.

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 battery will set you back around £600 ($780). That’s a massive saving when compared with buying a factory-built mid-drive electric bike.

 

cube acid hybrid one 400 electric mountain bike 2020 model

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 find someone who can fit the kit for you.

You will also need to consider the fact that a retro-fit 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.

Useful Links

In order 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 personal needs.  Both types of motor 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 basically 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.

direct drive hub motor installed on a hardtail mountain bike

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 at 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.

a small geared hub motor installed on a mountain bike

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 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.

Front wheel electric bike conversion kit fitted to a ladies hybrid bike

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.

bafang 250w hub motor electric bike conversion kit

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 have a tendency 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 a 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.

bafang 48v 500w cst rear hub motor kit with color display

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 set-up, 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.

Mid-Drive Motor

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.

a bafang bbshd mid drive motor installed on a hybrid bike

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 of 68mm-73mm wide and approximately 33.5mm diameter.

When installed correctly, a mid-drive system will give your bike the look and feel of a more expensive e-bike.

cube mountain bike with a bafang bbs02 and 52v battery

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 really 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 motor produce a significant amount of resistance with the motor off.

Mid-drives are definitely much better at hill climbing, a 250w Bafang BBS01B will produce nearly 100% more torque than a geared hub motor equivalent.

mountain bike fitted with a 1000w direct drive hub motor

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.

Conclusion

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 definitely 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.

Choosing the right e-bike 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.

36v 17ah battery hailong case

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 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 to. 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.

full suspension mountain bike fitted with a bafang bbshd

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.

It is advisable that you take measurements of your frame triangle before purchasing a battery. It is also worthy to note 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’

Thank you for taking the time to read this article, if you need any further help or advice choosing a conversion kit, please leave a comment below.

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2 thoughts on “Electric Bike Conversion Kit Guide – What You Need to Know

  • April 26, 2020 at 12:46 pm
    Permalink

    Thanks for the brilliant website…. lots of good advice. During the lockdown I have dragged my old commuter bike out out of the shed and put it back into service. I to regularly ride to work, but when I moved to a very hilly area it was relegated! I am now thinking that with some electric power I could start using it again……

    The complication is that it has a Shimano nexus 7 speed hub gear with a back pedal brake. That means either front hub motor, or convert to derailleur or….. would a mid mount conversion work with the hub gear….. or would it just break it?

    Any suggestions bearing in mind good hill climbing is a key for me

    Geoff

    Reply
    • April 26, 2020 at 7:22 pm
      Permalink

      Hi Geoff,

      Thanks for your complements, glad you like my website.

      There is a version of the Tongsheng TSDZ2 mid-drive that works with a coaster brake – here is the link.

      In my experience Shimano Nexus and Alfine hub gears work fine with moderately powered mid-drive motors. I have even installed several Bafang BBS02 750w motors to bikes with Nexus 8 hub gears without any long term issues. The Bafang doesn’t support the coaster brake function though.

      The Tongsheng is a good motor in my opinion, if you opted for the 350w or 500w version, that should give you enough assist for steep hills. I have tried these motors on 25% – 30% gradients and you still need to put a fair bit of effort in, but it doesn’t turn your legs to jelly!

      If you need any more advice, please let me know.

      All the best,
      Tony

      Reply

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