Auto Parts

Motor in  the front, rear wheel or a mid motor. Which system to choose to make your bicycle electric?

Advantages and disadvantages of the three most used systems in kits to convert your bicycle into an electric one.

How to choose the location of the motor to install on your bike? Here we give you a quick guide so you can choose the ideal kit to convert your bicycle into electric.

Spoiler: We will not tell you which system is the best, because the best does not exist: the convenience of one or the other system depends on the bike itself and the tastes and needs of the cyclist, but we will give you some clues so that you can choose yours.

Advantages of the mid drive motor

1.- The motor is centered on the bike and in the lowest possible position, so it lowers the center of gravity and helps balance the whole.

2.- The mid motor has a torque sensor. What is the difference between the torque sensor and the pedaling sensor? While going downhill with a small cassette in gear, you pedal “empty”: the pedals do not resist because the pinion does not transmit force to the bicycle. If the bike had a pedaling sensor, the motor would be activated because the sensor starts the motor simply when the pedals turn. However, a torque sensor would not activate the motor, because it only does so when pedaling transmits force to the wheels. Let’s say the torque sensor adjusts the motor aid to what is really needed.

The torque sensor saves battery power – obviously, since it doesn’t activate the motor if it’s not necessary – the sensations are more similar to those of a conventional bicycle and the power delivery of the motor is smoother and more progressive.

The torque sensor is not in itself an advantage. The choice of one or the other system is to the cyclist’s preference. We would not recommend the torque sensor to the lazy cyclists but to those who want to do more sport, maintain the sensations of non-motorized bikes, and save battery life.

3.- They deliver more torque than wheel motors. At equal horsepower, a center engine can deliver up to twice the torque of a wheel drive, and we will see that on difficult climbs: mid motors are generally better climbers than wheel drives.

4.- The mid motors react more quickly. The torque sensor responds immediately to the force exerted on the pedals, unlike pedaling sensors – which, with a few exceptions, usually mount the motors on wheels – which can take a short time to react. This delay is due to its design: magnets mounted on a disc attached to the pedal axis pass in front of a detector. Therefore, it may take a fraction of a turn for the engine to come into action from a standstill. We are talking about a delay of a tenth of a second, which in non-sporting uses is not the least important, but in off-road applications, it can be somewhat annoying.

5.- The motor controller and the torque sensor are integrated in the casing of the central motors, so they are elements that do not have to be installed separately, and therefore cleaner assemblies are achieved with less wiring. Some wheel motor kits solve the installation of the controller by integrating it into the battery.

6.- They are compatible with Shimano Nexus internal changes or similar.

7.- They are probably the easiest to install, but at the same time, they are the ones that need the most special conditions: they cannot be installed on all bikes.

the mid motor drive disadvantages

1.- The mid motor leaves the bike with a single chainring, which is usually also the one that comes standard with the motor itself. Do not think of it as a big inconvenience: the help of the engine will compensate for the reduction in the number of gears available.

2.- It is more exposed. The motor is located under the frame, so it occupies a position somewhat vulnerable to impacts. Although the engines have a well-protected exterior, this location can be inconvenient in certain rural uses, or if we are unlucky with one hit.

3.- The central motors are more expensive. At equal horsepower and battery, mid-engine kits can be up to twice as expensive as wheel-based motor kits.

4.- They cannot be installed on all bikes. In general, the vast majority of mid-engine kits cannot be installed in pressfit type bottom bracket systems, and those that support this type of axle are currently prohibitively priced.

In addition, there can be many other reasons why it is impossible to install a control unit: a simple cable guide, an excessive opening of the wheel hubs, the insertion or oscillation of the swingarm … can prevent this. You have to study the bike well before getting down to business.

A typical reason why a mid engine might not be installed is that the disc on which the chainring is fixed, it collides with the insertion of the swingarm of double suspension bicycles.

5.- They are incompatible with coaster brakes. If your bike has this braking system and you want to maintain it, forget about installing a mid motor.

6.- The box has integrated all the elements that the motor needs to function (controller, torque sensor …). This, which is an advantage from an aesthetic point of view because it results in cleaner installations, has the counterpart that repairs can be complicated and expensive. Sometimes impossible.

7.- It subjects the transmission of the bicycle to more effort. The force of the motor and that of the cyclist are transmitted together to the chainrings, chain and sprockets of the bike, therefore, the mid motor increases the probability of breaking the chain and greatly increases the cost of maintaining the bicycle as it forces to replace drive elements more frequently.

Rear wheel motor benefits

1.- Equal power and battery, they are much cheaper than those with a mid motor.

2.- They are suitable for all uses: they perform well on asphalt, on the loose terrain, country roads and in demanding off-road tracks.

3.- They are simpler and cheaper to repair than the mid ones – and this advantage is common with those on the front wheel. By carrying the controller and the independent pedaling sensor, it is easier to repair, and if necessary replace, these elements.

4.- There are rear wheel kits that allow both torque sensor and pedal sensor installation. Although we are not convinced by its operation, there are rear wheel kits that mount a torque sensor.

5.- They work without a chain. The effort of the engine is transmitted directly to the wheel, without going through the chain or the elements of the transmission. In case of chain break, the motor continues to run. This somewhat anecdotal circumstance can get us out of a hurry.

6.- They do not increase the maintenance cost of the bike’s transmission. Since the help of the rear wheel motors does not go through the chainrings, the chain or the sprockets of the bike, they do not put more stress on the transmission and therefore, do not increase the costs of maintenance of it.

Rear wheel motor drawbacks

1.- They are not compatible with internal changes. If you want to install a motor on the rear wheel of the bike and you have a Shimano Nexus or similar, you will have to forgo the internal gear and replace it with a conventional gear.

2.- They cannot be installed on rear wheels with thru axles.

3.- They are not compatible with coaster brakes

Front wheel motor benefits

1.- They are cheaper than those with a mid motor, and since the wheel does not have the core to couple the pinions, they are also somewhat cheaper than those with a rear wheel.

2.- Of the wheel type, they are the easiest to install, because they do not require the disassembly and subsequent assembly of the transmission, necessary when installing a kit on the rear wheel.

3.- They are compatible with internal changes. If your bike has an internal Shimano Nexus or similar that you want to keep, you can choose a front wheel motor.

4.- They are compatible with coaster brakes.

5.- They work without a chain. Like the rear wheel motors, in the front motors the effort of the motor is transmitted directly to the wheel without going through the chain. In the event of a chain break, the motor continues to run, a circumstance that can get us out of trouble.

6.- They do not increase the maintenance cost of the bike transmission. Since the help of the front wheel motors does not go through the transmission of the bicycle, they do not subject it to greater effort and therefore, do not increase its maintenance costs.

Front wheel motor disadvantages

1.- Although it behaves perfectly on asphalt, the front wheel with motor may have a certain tendency to slip on loose terrain. It is simply a matter of handling and we will quickly learn to compensate for this trend, but it is the installation we least recommend for use on mountain bikes.

2.- They are incompatible with a hub dynamo; Obviously not a big drawback: there are many solutions to power the lights, among others, systems that connect directly from the battery of your ebike.

3.- They usually only allow installation with a pedaling sensor, because there are very few front wheel motor kits with a torque sensor.

4.- They cannot be installed on bikes with thru axles on the front wheel.

By the editorial team of

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