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Choosing an Electric Bike Conversion Kit

Electric Bike

Choosing an Electric Bike Conversion Kit

When it comes to owning an e bike, you can either purchase a ready built electric bike, or build your own by choosing an electric bike conversion kit and installing it on a standard bike frame. If you’re thinking of going for the second option, we have all the information you need to get you started. There are many electric bike kit suppliers, so whether you’re hoping to build an electric mountain bike, or an e bike commuter, lets look at the options.

Electric Bike Kit – Mid Drive or Hub Drive

Electric Hub Motors

Hub motors are one of the most popular types of drive for electric bikes. They typically cost less than a mid drive unit, and are much easier to install for DIY e bikes. Hub motors are essentially electric motors that are contained within the hub of either the front wheel or the rear wheel.

There are a couple of different types of hub motor available. Firstly, there are direct drive hub motors that use the whole outer hub shell as the electric motor.  Secondly, there are geared hub motors, and these have a smaller internal motor. This motor uses planetary gears to drive the shell of the hub.

It’s worth noting a third type of hub motor that is starting to enter the market. These are “all-in-one” hubs or wheel systems that contain the entire set of e-bike components, including the motor, battery and controller inside the actual hub or wheel.

Let’s take a closer look at the pros and cons of the various motors.

Rear Electric Hub Motors

Generally speaking, rear hub motors push you so they have a more “familiar” feel than a front wheel hubs pulling motion. Since the power is delivered through the frame rather than the fork, rear hubs can have  pretty high torque and they are therefore available in a wide range of power levels.

E Bike Conversion Kit
A rear electric hub

Pros

Firstly, as mentioned already, standard bicycles have the rear wheel driving the bike forward. Rear hubs deliver their drive in exactly the same way, so for the rider, the power coming from the rear of the bike feels natural.

Having most of the rider’s weight also over the rear wheel, means there is much less risk of the rear wheel spinning on loose surfaces.

Just like other electric drives, many rear hubs will come with both throttle power options as well as pedal assist,  based on cadence (the revolutions per minute of the pedals).

Power options can commonly go from 250w all the way up to 1000w and beyond. Rear hubs are available in this wide range partly due to the fact that a good frame can handle this torque.

Another popular feature to look out for is regenerative braking, where some of the energy from applying the brakes is fed back into the battery.

Cons

Just like front hubs, rear hubs can start to lose some torque on longer steeper climbs. For that sort of terrain, mid drives are usually more effective.

Removing and installing the wheel, e.g. to fix a puncture, is harder work with rear hub motors.

Having the hub at the rear, combined with the rider’s weight over the back of the bike, can mean that the bike will handle very differently to a standard bicycle. If the battery is also on a rear rack, this is accentuated even more.

Front Hub Motors

Front hub motors are certainly one of the easiest e bike conversion kits you can install. Lets examine some pros and cons.

Front Hub Pros

Firstly, you can think of a front hub powered bike as a type of “all wheel drive” bike because you’ll have the motor driving the front wheel, while your pedalling drives the rear wheel. This can be offer an advantage if you’re riding on softer surfaces such as sand. It’s quite common to see “fat” electric bikes using a front hub motor to create this “all wheel drive” type of system.

E Bike Conversion Kit
A 250w front Hub Motor

Since the rear wheel remains standard, any type of standard bike gearing system can be used. Traditional gears with cassette, chain and derailleurs or also the less common internal geared hubs with a chain or belt drive.

As mentioned already, front hub motor systems are one of the easiest to install or remove from the bike, as there are no drive chain systems to deal with such as chain, derailleur and cassette. This can make it a little easier to fix a flat tire, or quicker to switch between electric power and a standard wheel.

Having the heavy hub on the front can also be balanced by positioning the battery inside the rear of the frame or on a rear rack. This can help prevent the bike from having an odd center of gravity.

Front Hub Cons

Firstly, being pulled by the front wheel, rather than pushed by the rear can feel a little strange.

Also, since most of the rider’s body weight is actually over the rear wheel, there can be a tendency for the front wheel to spin when accelerating, especially on looser surfaces or when climbing steep hills.

The more powerful the motor, the more pronounced this effect can be, but a little practice riding this sort of motor will help the rider counteract the effect by putting more weight over the front when necessary.

Front hub motors will typically be controlled by a throttle, and/or commonly have a pedal assist mode that’s based on your pedal cadence.

In terms of actual power, front hub motors are mostly limited to a lower power range of around 250 watts to 350 watts. You can purchase higher powered front hub motors than this, but these are less common because the front fork of most bikes aren’t structurally strong enough to cope with more torque than this. With this in mind, if you are building a DIY e bike and are considering a front hub motor, make sure you are building on a strong front fork, especially if you do decide to go for a higher powered motor.

Most e bike conversion kit manufacturers will be able to provide guidelines and recommendations on the front fork that is required for their hub. Alternatively, if you are thinking of buying a complete electric bike based on a front hub motor, then the company selling the bike should built the model using an adequate front fork to handle the motor’s power.

Another disadvantage of front hubs is that they have a tendency to lose momentum on longer, steeper climbs. This is where you may find a mid drive motor is a better option, as they are known for being better at climbing long and steep hills.

E Bike Kits for Mid Drive

Until fairly recent times, mid drive kits were a less attractive option than hub kits. They tended to only come in 250w power option, unless you were willing to pay huge amounts of money. Now, there are many options on the market, and prices across the full power range have become a lot more favourable.

Electric Bike Conversion Kit
mid drive motor kit

A few benefits to choosing a mid drive kit over a hub motor:

  1. A mid-drive puts the weight of the motor low and centralin the frame, giving the bike much better handling characteristics.
  2. A mid drive will almost always out climb a hub motor. If hills are your thing, you should probably choose a mid drive over a hub drive.
  3. A mid drive motor can make full use of the bike’s gears, so it’s more efficient, which can also mean more range than a hub motor for the same battery capacity.
  4. Being able to use the bike’s gears means the motor can be smaller and lighter and still offer a wide range of performance.
  5. You are less likely to break spokes than you are with a heavier hub wheel, especially if you ride over potholes etc.
  6. Swapping wheels and fixing punctures is much easier with a mid drive.

Some of the bad points with mid drive kits:

  1. Price. Mid drive kits are usually more expensive than hub motor kits.
  2. Complexity. Installing a mid drive requires more technical skills than installing a hub motor, so for DIY builders, a hub drive can be more appealing.
  3. Noise. If you’re looking for a quiet stealthy e bike, hub motors are usually quieter than mid drives.
  4. Clunky gear shifting can be a nuisance. To really get the full benefit of a mid drive, you’ll need to use those gears, and not all mid drives cope with gear changing particularly well.
  5. Reliability. More moving parts can mean a mid drive can be less reliable and maintenance free than a hub motor.
  6. Drive chains will take a beating so be prepared to replace chains and gears more regularly due to wear and tear.

250w or 1000w – What Size of Kit Do I Need?

There’s no single answer to this question. The size of motor you need will largely depend on the type of riding you want to do on your electric bike. Whether you are using your ebike as a commuter, or as an off road beast that requires a fast electric bike conversion kit, these factors will determine the best choice for you.

250w is generally the smallest motor you should consider, and is one of the most common sizes in use on ebikes at the moment. If you’re going to be commuting mainly on flat, well surfaced roads, with few if any hills, then a 250w motor could be the perfect choice for you. This would be more than enough to take the effort out of the ride, and will be very efficient in battery usage. If you are a heavier cyclist,  although 250w will be fine, you may want to increase this slightly to a 350w motor as it will just provide that little more power when needed on the occasional hill.

If you are intending to use your electric bike off road, and want to blast up lots of steep hills, then you really need to look for something in the 500w to 1000w range. These motors are very powerful and will propel you up any incline at speed.

It’s worth keeping in mind though, that motor sizes are just part of the equation. As discussed already, mid-drive motors can make full use of the bike’s gearing, and so you may find that a mid drive kit perform better on hills than a hub motor. Many pre-built e bikes designed for mountain riding use mid drive kits motors for this reason.

Also bear in mind that the bigger the motor, the bigger the battery you are going to need. Biggers batteries also mean more weight so there is a trade off here, plus batteries are expensive and size increases the cost, so you will need to keep this in mind too when you’re choosing a motor size.

Electric Bike Motors and Legal Considerations

There’s also another important thing to consider when deciding on which size of e bike conversion kit to buy. There are legal restrictions in various countries that govern the size of motor and top speed allowed buy law.

In the UK cyclists are severely limited, and the motor’s maximum continuous rated power output must not exceed 200 W for bicycles, 250 W for bicycle tandems (i.e. two seaters) and 250 W for tricycles. I am completely confident that this will change as the reality of gas shortages finally dawns on the United Kingdom’s legislators.

According the UK Government’s website at the time of publishing this article:

…if you’re 14 or over you don’t need a licence to ride electric bikes that meet certain requirements, and they don’t need to be registered, taxed or insured.
Electric bikes meeting the requirements are called ‘electrically assisted pedal cycles’ (EAPCs). They can be 2-wheeled bicycles, tandems or tricycles.

EAPC requirements
The requirements are:

  • the bike must have pedals that can be used to propel it
  • the electric motor shouldn’t be able to propel the bike when it’s travelling more than 15.5mph
  • the motor shouldn’t have a maximum power output of more than 250 watts

It must also display one item from each of the following:

  • the power output or manufacturer of the motor
  • the battery’s voltage or maximum speed of the bike

Where you can ride an EAPC
If a bike meets the EAPC requirements it’s classed as a normal pedal bike. This means you can ride it on cycle paths and anywhere else pedal bikes are allowed.

Other kinds of electric bike
Any electric bike that doesn’t meet the EAPC rules needs to be registered and taxed. You’ll need a driving licence to ride one and you must wear a crash helmet.

The vehicle will also need to be ‘type approved’ to make sure it’s safe to use on the road.

Of course, if you only plan on using your bike off road, e.g. on private ground, then you can be a little more adventurous with your choice of motor and power level.

E Bike Battery Options

Batteries are expensive. Aside from having the correct voltage, there are two important factors in choosing a battery for your electric bike. Capacity (Which determines the range you can ride between charges) and weight (which will affect both handling, and to some extent, the range). Technology has improved a great deal over recent years, with heavy lead acid batteries being replaced by a number of newer types of battery, bringing us to today’s e bike batteries of choice, Lithium-ion (Li-ion).

Electric Bike Conversion Kits
36V 11Ah HalloBattery

Lets take a closer look at some different battery technologies.

Lead-acid Electric Bike Batteries

Lead-acid batteries are cheap and can be recycled fairly easily. but they need to be carefully handles and they don’t last all that long. Although you will see these types of batteries used on electric bicycles, they’re not very common nowadays. There are several reasons why lead-acid batteries are cheaper than other types, mainly that they can weight 2 or 3 times more than other types of battery, and their capacity is significantly less. If you are looking at any e bike conversion kits that state they come with a lead-acid battery, or if your unsure of any included batteries and suspect that they may be lead-acid, it’s a good idea to look elsewhere.

Nickel-cadmium (NiCd) Batteries

Nickel-cadmium (NiCd) batteries are a step up from lead-acid batteries and have greater capacity. Before you start to consider this type of battery though, you should know that nickel-cadmium isn’t cheap, and cadmium is bad pollutant which is very hard to recycle. Although they will last a little longer than a lead-acid battery, their risk to the environment and recylcling cost mean they’re not really a suitable option for electric bikes.

(NiMh) Nickel-metal Hydride Batteries

You may also have heard of NiMh batteries. While these are more efficient than NiCd batteries, they can also cost more,  and in use, most people’s experience is that NiMh provide very little improvement in range over NiCd. They are easier to recycle than NiCd batteries and last longer, but regardless of this, they’re really not a good option for electric bikes.

Lithium-ion (Li-ion)

Finally, we come to the current battery type of choice. Lithium-ion batteries are now the most common electric bike battery type. Again though, not all batteries are created equal, and there are many different kinds of Li-ion batteries to choose from. Li-ion batteries are the preferred option right now, as they last longer and generate more power for their weight than other types of battery. They’re not perfect though, as they require careful charging, using proper battery management, and they do come with a fire risk if they’re not handled correctly. If you buy a Li-ion battery specifically for e bike use, all of this will be taken care of by the manufacturer, but this comes at a cost and they can be an expensive investment, often costing a good deal more than the motor.

Lithium-ion Polymer (Li-pol)

This is a new kid on the block, and although similar to Li-ion in terms of price, weight and capacity, it does have the added ability to be made into various shapes. There are no liquid electrolyte parts to these batteries, so they don’t require the heavy protective cases like other battery types. They are also more stable so could be perfect for electric bikes and other electric vehicles. Time will tell.

Some Notable Others

Lithium Cobalt : This is another type similar to Li-ion. It’s claimed to have a much higher energy density than other lithium type batteries,meaning more capacity for less size and weight.

Lithium Manganese : Some say it is the best battery type of all, but its too early to say for sure. Again, this is one to watch.

Final Word on E Bike Batteries

When it comes down to it, Lithium-ion is the current preferred option. To ensure you get the best from your battery, keep it properly charged according the manufacturer instructions. The best way to extend the life of your battery is to charge it often. Charging up a Lithium-ion battery before fully depleting it is actually a good thing to do, and the best way to increase performance and lifetime on a lithium battery is to lower the number of deep discharge cycles as much as possible.

There’s a train of thought that says you can double your battery’s life expectancy by discharging only half of the capacity instead of three quarters, and that you will get six times the battery life if you only use 30% of the battery before each full charge.

Electric Bike Conversion Kit

Choosing a Frame and Fork For Your Electric Bike Conversion Kit

So you’ve chosen your motor type and power, and decided on a battery. You may already have a bike frame, or a full bike that you intend to convert, but if not, you’ll need to choose a bike frame, and fork. The key consideration here will be the suspension type: No suspension, front suspension only, or full suspension. Each has their benefits, so lets take a look at them. These will all have significant implications, not least the positioning of the battery.

Where are you going to put the battery?

Mounting a battery on the rear rack on a bike is pretty common, but be aware that a full suspension bike can make this tricky because the rear end is floating. You will need to check the travel of the rear wheel does not allow it to come all the way up and hit your battery. To prevent this, you will need to mount the rear rack battery higher than you would on other types of frame, and this will affect the center of gravity.

It is possible to mount the rack on the rear suspension arm ,so that it moves up and down with the suspension. This is a much better mounting option if you have full suspension, but it’s not always possible so do your research.

Full Suspension:

A frame with full suspension will have only a small amount of space for the battery in the center of the frame, so with this type of frame, you may need to mount the battery on a rear rack. We’ve already discussed having too much weight at teh rear, and the implications so keep this in mind.

Front Suspension only:

When you only have front suspension there is much more room inside the frame’s central triangle for a battery (you can purchase triangular battery bags), and of course having the battery in this location means a much better balanced bike.

No Suspension :

If you only plan on commuting, mainly on good road surfaces, you may not even need suspension at all. There will be an element of suspension achieved buy choosing the correct size of tyre, and of course with no suspension you benefit from having lots of space to mnount your battery inside the frame’s triangle, and overall the whole bike will also be much lighter. This could translate to achieving greater range per charge (and make the bike easier to pedal if your battery runs out).

Still not sure? Here is a list of good and bad points around suspension:

The Good Points to Having Suspension:

  • Comfort – there’s no doubt suspension will smooth out those bumps in the road
  • Aesthetics – Some suspension just simply looks cool
  • You can get good suspension for relatively low cost so price isn’t really a factor in making your decision

Cons

  • There’s less room in frame triangle for batteries on full suspension bike frames
  • It can be harder to mount a rear rack on rear-suspension bike frame
  • suspension will increase the weight of the bike
  • its another component to maintain and potentially cause problems
  • if you are considering a front wheel drive hub many front suspension forks aren’t strong enough to cope.

Summary

There are lots of things to be considered before you start buying your conversion kit. Building an electric bike can be incredibly rewarding, and time spent researching at the beginning will be well worth it in the end. We hope you found our guide to choosing an electric bike conversion kit useful and wish you every success with your build! If you’re thinking about purchasing an e bike conversion kit and you’re wondering what is the cheapest electric bike kit, why not take a look at our great range of kits and e bike batteries for some great deals.

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