How To Build An Electric Bike From Scratch

How To Build An Electric Bike From Scratch

Are you good with your hands (or know a little bike maintenance)?

Have you thought to build an e-bike for yourself?

If you have a smaller budget than could buy a midrange electric bike you could build one at least as good – if not better – than any on the market today for a similar budget.

Here we discuss how to build an electric bike in a wide variety of ways, from a lethally quick speed demon to a fun project that will get you about town. It really is down to your imagination!

Beginning with a guide as to how to design your e-bike, we look at how to build an electric bike while only gently stretching your existing skills. Starting at the easy hobbyist’s end and going to the engineer’s fun quest at the other, let’s cover all the bases of building an e-bike from a kit or from scratch.

Design your electric bike

Do it yourself electric bike

Before you go out and buy anything you need to know what e-bike you’re about to put together. Here are a few questions you need to answer before buying the components or kit for the eventual machine.

  • How skilled are you on bike maintenance? If changing a tire is about the most involved you have been then perhaps a front hub motor would be the best way forward. If you have better bike mechanic skills, or just want to stretch yourself then in order of difficulty, the rear, crank and DIY options may be your choice. Be aware the DIY option can be extremely difficult to do!
  • Is this a bit of fun or do you want to set up a decent alternative to buying a pre-built e-bike? This will determine the bike you use as a platform. Don’t go wild buying a top-end new bike but do consider a good quality secondhand one for a good quality result, though that old machine sitting unloved in your garage could be a fun project for a lower overall cost.
  • The same question applies to the kit you buy too. The crank motor kit will cost close to $1000 and more while a quick and easy fit will be a front hub motor for as little as $300 at the other end of the scale.
  • How fast do you want to go? If you want to go 30mph-plus you want a rear hub motor as it can take motors of 750W and more without bending the forks or spinning out when you accelerate.
  • Are there any big hills in your area that you need to climb? This has two answers. The cheaper option would be a rear hub motor as you can put a more powerful system in. The better option, though a lot more expensive and harder to fit, would be a crank motor kit.
  • What sort of distances do you want to go? This will dictate how big a battery you need (often the most expensive component). You can also cycle more economically on the battery by fitting a pedal assist system (PAS) that comes as an option with front, rear and crank motor kits. You will need more tools and time to fit this.

With these answers in mind let’s now look at the questions above in more detail, including what’s required in how to build an electric bike with these kits and components.

Bike

Cruiser Bike for DIY Electric Bike

One of the disadvantages of buying a cheap, fully fitted e-bike is that you may have good quality e-bike components, but you will generally have a not-so-good bike as a platform.

Even in the $700 – $800 price band you may have disc brakes, forks with shocks and a Shimano gear system but these will be baseline options at best. It may look good but you’ll break a sweat picking it up thanks to its weight!

This is why with a little care you could fit similar components to those fitted by the cheaper OEMs to a better machine. Even a five year old mountain bike that once retailed for $1000 plus could be bought for relatively little money. This will have lighter, decent quality components.

We do recommend you buy a solid machine like a beach cruiser or a mountain bike as though not designed for the added stresses of an electric bike system, either will be over-engineered to tackle the stresses of the trail, and in the case of the beach cruiser will have chunky components as part of its look.

Where it comes to fitting a crank or ‘mid-drive’ unit, look for a machine with a 68mm-73mm threaded bottom bracket. Many newer bikes have a press-fit bottom bracket so would be unsuitable. Others have non-standard sizes.

Take a measuring tool before you buy.

A final note is to either be ready to retrofit a mechanical disc brake system or to choose a bike with one over another with a hydraulic disc brake system. Disc brakes are far better for stopping safely from high speeds. Cable operated mechanical disc brake systems are easier to modify for the final fit of the kit.

Consider fitting torque arms to any machine with a hub motor as they will spread the load forces from acceleration. Torque arms could allow you to build an electric bike with a hybrid or road machine too.

As to the unloved old bike in the garage? Better to use it than to throw it away! It could have a decent heritage and be just the platform you want anyway. Do think of the criteria we discuss above.

Battery

Electric Bike Battery

The final design consideration before we go into how to build an electric bike is the battery:

  • How fast do you want to go?
  • How far?
  • Where do you want it fitted?

The faster the bike the higher the voltage. A 24V system will get you to around 15mph on the flat on a front hub e-bike. Faster, more powerful e-bikes will need a 36V-48V system as that will take you to a comfortable 30mph, though your limit for a front hub system will be 36V as, as discussed above you will get a fair bit of torque out of it. Batteries go up to 72V for extremely quick and powerful systems.

The Amp-hour (Ah) rating is the next thing to consider. These go from around 5Ah up to 20Ah for a decent long range battery. You will get what you pay for in terms of range – the cheapest will be at the lower capacity and the most expensive at the higher end.

If at all possible, stretch to the higher end of the spectrum as a higher capacity battery will run cooler and last more charges than a cheaper, lower capacity one.

Batteries come in three broad types – the first is a pannier-mounted battery that sits over the rear wheel puts the weight in a less comfortable position but can be easier to fit.

The frame-mounted battery sits in the triangle of the frame and puts the weight in the center of the machine.

A final type sits in your handlebar basket and is good for an easy fit on a front-hub system. This puts the weight where you are controlling the bike and is not recommended for a heavier, larger capacity system as it can alter your maneuverability negatively.

How to build an e-bike

How to build an e-bikes

Now you have the design in your head we will look at how to build an e-bike.

With the kits there will usually be a YouTube video and/or paper instructions as to how to put the system together. You will still need some intelligence and thought of your own to put the machine together in a way that doesn’t look a complete mess!

A note on timings – don’t believe what the instructions on your kit say regarding how long it will take. Unless you are a skilled mechanic or electrical engineer (let’s face it: most aren’t), take the time suggested in the manual or YouTube video and double it.

Generally, that will mean 2-3 hours for a front or rear hub system, five or more for a crank motor, and longer for a scratch DIY build.

Front hub

eBike Front hub

Where it comes to how to build an electric bike, a front hub kit is going to be the easiest.

You will need basic bike mechanic skills, the tools that you have for that maintenance, tools for simple wiring, and some judgment as to how it looks and feels.

The kit will come with a wheel that has been pre-threaded with spokes and the rim. If you have gone out and bought a secondhand bike to convert, or are using an old but quality bike as a platform, think about the tire they supply – this might not be brilliant so you may need a new tire that suits your needs or to swap the tire on the old front wheel onto the new wheel.

If it has disc brakes, you will need to fit the old disc (or a compatible new one) to the new wheel too.

The wheel itself should go on quickly. Spin it to see if it rubs anywhere. Hydraulic disc brakes are a little bulkier, which is why we suggested a mechanical system above – replacing will take more time but should prevent the unwanted friction.

You then fit the torque arms to the fork and wire up the loom, controller and battery. After any brake replacement/servicing this will take the most time as you need to fit it right and neatly. Ultimately the look is going to be important to your handiwork – you don’t want it to look like an old bag of spanners at the end of the day!

Where will the battery go? The simplest and easiest will involve putting it in a front shopping basket. More careful wiring can use a frame battery. It is least advised to fit a pannier mounted battery in this case as it is a harder job to place the battery in a worse position than on the frame in terms of weight distribution. 

In most cases, you will not want a Pedal Assist System (PAS) but if you do this requires opening the bottom bracket to fit the sensors. You’ll need a bottom bracket removal tool and a crank pull. Many kits with a PAS sensor will supply these, but it may help to buy your own. This requires a lot more care and skill than the throttle-only system.

Rear Hub

You can have a more powerful e-bike motor with a rear hub system but it will take more time and effort to fit. You may need the equipment to fit a new cassette to the wheel, or put the old cassette on the new wheel should it be of higher quality and you don’t want to fit a new chain.

Wiring is more difficult than on a front wheel hub kit too – bear this in mind when it comes to making space in your day to build the electric bike system.

You also need to think about disc brakes as above as well as fitting torque arms (even if not supplied) so you can optimize the ride of the machine at the end.

You should follow the directions and any available YouTube videos as to how to build the electric bike, making any modifications as you feel necessary to make it look and feel right.

The battery can go on a special pannier rack that has a battery holder as part of the frame. It doesn’t take too much extra effort to use a frame battery here – you will still need cabling to the handlebars for the controller and throttle so extra cabling to the frame won’t take a lot of extra effort for a better overall build.

The PAS option will also take a bit more time (an hour or so for the uninitiated) but will deliver a better battery economy.

Crank Motor

Crank Motors

Though a front or rear wheel hub kit will cost as little as $300 including a battery, be prepared to spend $1000 on a crank motor kit before the battery.

The work involved is not easy either, and for someone with just a little knowledge of bike maintenance, this probably isn’t the job for you. That said, you will have a rocking e-bike for your efforts!

Before you balk at the price, remember that unlike Bosch or Shimano mid-drive motors fitted to European machines, the Tongsheng and Bafang kits are serviceable.

That means for a similar outlay to a midrange mid-drive e-bike you will be able to have a machine that can be fixed when it breaks. You could keep the bike on the road for a great many more miles than you might a pre-built mid-drive e-bike.

Building a mid-drive e-bike requires most of the work on the bottom bracket.

You will have selected the correct bike from our discussion above. You’ll use a bottom bracket removal tool and crank puller to remove the guts of it and then rebuild it with the components in the mid-drive kit. You then re-install the cog, chain and pedals before wiring up the controller, sensors, throttle and battery.

DIY

We will briefly look at how to build an e-bike from scratch here. To do this you will be the sort of person who might have rebuilt a car, boat or motorbike, and enjoy inventing things.

The basic components are:

  • A 250 Watt + motor
  • A controller to translate the input to an output
  • A throttle device (or PAS if you’re super clever!)
  • A battery.

From there it is down to you.

Can you thread the spokes on a wheel?

Build a hub motor e-bike.

How else could you improve on existing designs?

One idea that a very inventive guy had to build a basic e-bike was using the parts from a battery-powered drill. Have a look at his video here:

Meanwhile this UK student 3D printed much of the new components for his machine:

Good luck in your build

So there you have it – a range of design and build options discussing how to build an electric bike. 

You can see dozens of different outcomes of different e-bikes that could come from the suggestions we make, and it is down to your imagination as to what you could end up with.

If you do get around to building one for yourself, do let us know and we’ll get it out on our network for the world to see.

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