What is an Electric Bike?

Essentially, an electric bike is just like a normal bike but with the benefit of an on-board electric motor. There are various types available but, with the aim of keeping things simple, the most common e-bike today is a ‘pedal-assist’ or ‘pedelec’ bicycle.

As the name implies, a pedal-assist bike has an onboard electric motor that is designed to supplement the amount of physical input from the rider and does not activate until the pedals are already in motion. The idea being that you can ride a bike as normal but with the benefit of added propulsion when the going gets tough.

The motor is powered by a rechargeable battery and how much pedaling you do will dictate how long the battery lasts. If you do the bare minimum, then the battery will last for 20 miles or so. Do a bit more work and the further you can go…

All electric bikes have a blend of key components, aside from the obvious things such as a frame, handlebars and wheels.

  • A battery, (typically lithium-ion) frame or rear-rack mounted. Some bikes also have the battery integrated into the frame itself. And. a motor, crank (central drive) or hub mounted.
  • Motor Control Unit (MCU) located near to the battery or built into the motor unit. This is the clever piece of technology which controls the output of the motor depending on how hard you are peddling and if you are using the brakes.
  • Sensors mounted in the crank or on the wheels which send speed, direction and torque data to the MCU.
  • Brake sensors which signal the motor to stop generating power under braking for both safety reasons and to protect the motor itself.
  • Display unit, usually fitted to the handlebars for easy viewing. A good unit will display speed information, distance travelled, range remaining based on current use.

A pedal-assisted electric bike or pedelec is classed as a Type 1 bike and will typically have a governed top speed of 15.5 mph (25 kph). This means the bike is considered safe to used wherever a normal bike would be without the need for a license or insurance.

The top speed only applies to the motor output, and you can, of course, travel faster than this depending on how hard you pedal.

Types of Motors and Propulsion Systems

The motor is, obviously, the main component of an e-bike and there are basically two types. Hub motors, which can be fixed to the front or rear wheel, and mid or central drive motors which are fixed at the base of the bike’s frame and connected directly to the pedals.

bosch central drive
Bosch Central Drive Unit

The type of motor and where it is fixed will have a major effect on how the bike handles.

Front-hub motors are the simplest option but have the most limited capability. Typically, front-hub units are fitted to low-budget bikes or as conversion kits for regular bikes. As with a front wheel drive, there is a compromise in terms of handling and cornering at speed can be tricky since a lot of weight is placed at the front of the bike.

Rear-hub motors can also be retro-fitted to a standard bike although the process is a little more complex. They do have the advantage of better handling though since the weight is distributed to the rear of the bike and this makes for better handling overall.

Hub motors are sealed units and are basically maintenance-free. They do offer a good solution for anyone who does not want to spend a large amount of money on a bike are fine for regular medium/short distance journeys and occasional recreational use.

Central Drive Motors are mounted at the base of the frame, which is ideal in terms of balance and handling. Central drive units produce higher torque than hub motors and tend to be the unit of choice for the best pedal-assisted bikes.

Because the motor is connected to the crank directly you get a much more effective and smoother transfer of power to the rear wheel.

Sensors within the motor will gauge the amount of rider input via the pedals and adjust their output accordingly.

Manufacturers of the best central drive motors include Shimano, Bosh, Brose and Yamaha.

Motor Technology

The electric motors fall into two main categories:

  • Brushless DC Motors (BLDC)
  • Mid or Central Drive

A Brushless DC motor is similar in design to a standard DC motor you may find on a number of domestic appliances except that the windings are stationery, and the magnets rotate around the hub. The benefit of this design is that there are no carbon brushes to wear out. Brushless motors can be fitted with or without sensors, the latter being preferable since this allows the motor to react with more finesse to the amount of input from the rider.

These kinds of motors employ planetary gearing that will eventually wear and need replacing.

Mid or central drive motors are less conspicuous and have the advantage of being directly connected to the pedals, chain and gear set. The result being the ability to use lower gearing which results in easier take-off, improved torque and, where it really matters, more assistance when riding uphill. And, because of improved efficiency, more range per kWh from the battery.

Hub, or mid drive motors therefore are the ideal option although they are more expensive, require more input from the rider in terms of gear changes and, because of greater load on the chain and gearing, will require these items to be changed more often. The motors themselves are very durable though and practically maintenance-free.


Battery technology has advanced leaps and bounds over the past few years, and it is this advance in technology that has made electric vehicles a reality.

The commonest type of battery used for all types of electric vehicles today is Lithium-ion (li-ion). There are several types of li-ion battery, but they all share the same basic characteristics.

They are rechargeable and have a long life, typically between 500 to 1000 full charges. Whilst you can expect a li-ion battery to last much longer than this you will notice a gradual degradation of performance over time.

With a battery there is always a balance of four main features:

  • Lifespan
  • Power storage per kg of weight
  • Cost
  • Safety

The range you can expect from a battery depends on a balance of the above properties together with the weight of the bike, weather, terrain and rider input.

As a guide, ranges vary from 25 miles to 100 miles depending on the above factors. Of course, even when the battery is fully depleted, your bike can still be peddled as normal, so you are never going to be left stranded.

Modern li-ion batteries are very reliable and usually last well beyond their indicated lifespan. Battery failure due to defects is also very rare.

What is certain though is that battery technology is advancing at an impressive rate, and this means that over time they will continue to become cheaper, lighter and perform better for the foreseeable future.

E-bike designs & technology continue to improve and there is no doubting their increasing popularity. Whilst no one can predict the future it is fairly safe to say that motor and battery performance will keep getting better and, as with all technology, will become cheaper as economies of scale are factored in.

See Also
Sainsbury's cargo bike delivery
e-Cargo Bikes – the Future of Home Delivery
Electric Trikes for Those with Mobility Issues