DIY electric bike: assembly nuances


Is it difficult to make an electric bike yourself, with your own hands? Let’s figure it out.

On Aliexpress, a huge number of both ready-made electric kits and individual components for assembling an electric bike are available for order.

When you immerse yourself in all this variety of components, your eyes light up, and you start dreaming of how to install them on your bike, you do a lot with your own hands, including electrics.

And now, the components have been ordered, and they are already at your home. You try them on a bicycle, and at that moment questions start to arise, and your eyes are no longer burning so brightly …

But let’s start in order. What are the nuances we will encounter when assembling an electric bike on our own?

Installation of the central motor in the carriage assembly

The most important thing, of course, is not to be mistaken with the carriage size. However, this is not the only thing to pay attention to.

Often, when installing the central motor, it simply does not fit into the hole for the carriage — due to the weld inside the carriage hole. In this case, you need to use a reamer of a suitable diameter, but you can also do with a file.

In addition to the welds inside, the installation of the motor can be interfered with by the frame elements from the outside — the same welds or reinforcement elements. How to deal with them is a separate question.

And now the motor is inserted. To fix it, the kit includes union nuts and a bracket. But before tightening the nuts, you should pay attention to whether the star rests on the frame feather.

The fact is that there are quite a few bicycle manufacturers, but there are many more frame options that they produce, and these frames are not designed for installing electrical kits.

If the star still rested on the nib, a spacer ring must be made to provide the required clearance. But then there may not be enough thread to screw the nut onto the engine — in this case, installation is impossible (of course, unless you decide to make a new star of a smaller diameter, thereby changing the operational characteristics).

And since we touched the sprocket, we need to make sure that the chain line (when viewed from above) is perpendicular to the centerline of the rear wheel in the middle gear of the rear derailleur.

If this is not the case, the diagonal loads on the chain arising during operation will lead to it jumping off the stars, and sometimes even breaking.

But the correct value line does not guarantee a clear operation of the system during operation, since when changing gears, especially if the engine is running at this moment, the chain can jump off the star of the motor.

To eliminate this phenomenon, a chain catcher is manufactured. Sometimes the front derailleur can be used as a catcher by setting it to the correct position.

Quite often, there is a hydraulic line from the rear brake under the carriage assembly. And if it fits into the gap between the frame and the engine, then during the operation of the latter, a torque will arise that will transmit it.

This torque is high enough to crank the engine, no matter how hard you tighten the nuts. Therefore, you will have to provide an emphasis for it, and remove the hydraulic line from under the engine and let it pass by, having made a separate mount for it.

Installing the wheel motor

The motor-wheel is much easier to install than the central motor, but there are some nuances here.

Basic — if your bike has an axle mount, then the motor-wheel cannot be installed in it. The motor-wheels are installed only on the QR mount (Quick-release), with an eccentric.

However, there is an organization that competently manufactures adapters from axial fastening to QR just for such cases — this is a company

The second thing to pay attention to is that the motor must have installation dimensions corresponding to the distance between the bike’s dropouts. Otherwise, when installing the motor-wheel, the rear stays will either have to be compressed or stretched — this will all lead to additional loads on the frame, which will affect the reliability of the structure as a whole.

During operation, the motor-wheel generates a torque that tends to turn the axle inside the mount. And since this moment is quite high, it is necessary to install torque arm — dropout amplifiers.

Torkarms should fit snugly on the engine axle and be firmly attached to the dropouts. Due to the many options for making frames, there are no universal torcs, so finding and making them is a very creative process.

Battery mount

On aliexpress, you can order both a quick-detachable battery, in a case and with a platform that is attached to the frame, or a simple «brick», and then start to figure out how to fix it.

In the first case, it is enough to fix the platform to the frame, as a rule, it has holes for attaching a water bottle to a stationary place. Although, this is not the most reliable option, and it is better to supplement such fastening with clamps in the shape of the frame, as the same ones do.

By the way, if you have a double suspension (in addition to the suspension fork, there is a rear shock absorber), or a frame with a lowered upper tube, you need to pay attention to the fact that the shock absorber may interfere with the installation of the battery inside the frame triangle.

If we are dealing with a «brick» type battery, that is, assembled and packaged in heat shrink, but without a case, then securely fixing it on a bicycle is a much more serious task than it might seem at first glance. Since even a slight damage to it can lead to serious consequences. But I will write about this in a separate article.

And right away I would like to say about the option of placing the battery on the trunk — when driving, it starts to sway and eventually breaks the trunk, or flies off it. So I don’t recommend this option.

There is also the option of separately purchasing battery components (Li-ion cells, BMS board, wires, connectors) and assembling a lithium-ion battery with your own hands, but there are even more nuances that I will describe in a separate article.

Mount the controller

In the case of a central motor, the controller is usually installed in the motor itself, and in the case of a wheel motor, it is taken out as a separate component.

In the set with Aliexpress, along with the controller, there is often a separate plastic case. This body has two holes for mounting on the seat tube instead of a bottle mount.

This option is good in that the wire connections are hidden in this case, and thereby partially protected from the external environment.

If the kit does not include a separate housing for the controller, the latter will have to be fixed independently. Many people use bicycle bags for this, but this is far from the best solution, since open connectors oxidize under the influence of moisture and the electric bike stops working.

Silicone is often used as a solution to the problem of tightness of the plastic case of the controller, but the most correct solution would be to replace the wires with connectors with sealed ones, for example, manufactured by «Julet» — this is a modern and reliable solution.

PAS sensor

To use the assistant riding mode, that is, when you pedal without touching the throttle and the motor helps you, a PAS sensor is installed on the e-bike. It consists of a ring with magnets, which fits on the pedaling axis, and a Hall sensor, which is mounted on the carriage.

Thus, to install the PAS sensor, you need a connecting rod puller and a special wrench to unscrew the carriage. It makes no sense to purchase these tools for one use, so you have to take your bike to the nearest bike workshop.

However, it should be noted that if the ring with magnets is installed the other way around, the system will not work. So it is better to immediately check the performance on the finished bike.

Brake sensors

For safe use, brake sensors are installed on the e-bike, especially if you have a powerful motor. They are necessary in order to turn off the engine in the event of a pressed brake lever.

The set with Aliexpress most often comes with cable brake levers with built-in buttons. So if your bike has hydraulic brakes, these will not work.

In this case, you can show your engineering thinking yourself and find a solution, or you can send your hydraulic brakes by a transport company to

If you know other companies that are developing reliable brake sensors for hydraulics, please write in the comments so that readers can get more information and have a choice.

Throttle stick

It would seem that there is nothing easier — remove the grip, cut if necessary, install the throttle handle, return the grip. But here, too, nuances arise — the handle most often begins to overlap the gearshift levers, and they will either have to be filed or increased.


The diameter of the handlebars for which the display is designed should match the diameter of the handlebars on your bike. This should be checked in advance.


If you analyze Aliexpress offers, with central motors, as a rule, there is a sealed wiring with sealed connectors. But with motor-wheels, open wiring most often goes, which is in no way protected from the external environment (except perhaps the plastic case of the controller).

It is logical that for the versatility of Chinese electric kits, the lengths of the wires are made with a margin, and when all the components of the system are installed on the bike and connected, the excess wires will need to be hidden somewhere.

In addition to compromising the aesthetics of the e-bike as a whole, excessive length of power cables from the battery to the controller and from the controller to the motor creates additional resistance that reduces the efficiency of the system.

Recently, among Aliexpress’s offers, kits with an integration cable have appeared — this is when a controller is connected to it from one end, and a throttle stick, display and brake sensors on the other (from the steering wheel). But this cable, of course, comes with a margin of length, and it will also need to be rolled up somewhere.


Hopefully, in this article I have described, if not all, then most of the nuances encountered when installing an electrical kit on a bicycle on your own.

I will do a detailed analysis of each component of the system in the following articles, so subscribe to my channel.

Thank you for your time.

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