Electric bike drivetrains_ internal vs external gears
An electric bike or bicycle is one with an inbuilt electric motor to aid the easy movement of the bike. These motors can either help to increase the rider’s pedal power or to provide extra throttle to the bike.
There are other mechanisms called drivetrains that help the motors perform these functions. What sets the electric bike aside from motorcycles is that manual pedaling is still required irrespective of the type of motor or drivetrain it uses.
An electric bike drivetrain simply refers to the system that transmits power from the bike rider to the drive wheels of the bike. This system usually consists of a mechanism for power transmissions such as a chain, crankset, wire rope, pulley drive, or a gear system. When it comes to electric bikes, there are very few drivetrain options to choose from, some of which are discussed below:
Bottom bracket gearing
Bottom bracket gearing is an enclosed gearing system positioned around the axle and pedal of the bike. This type of gearing system reduces the wearing and tearing of the gears because the motor power doesn’t go through them. However, it can increase the bike's weight and reduce its efficiency.
Continuous Variable Transmission
Continuous variable transmission is another type of gearing system. This system does not have a specified number of gears; the speed just keeps increasing or decreasing as the rider twists the handgrip or presses a button. This system carries out automatic gear changes, which make it easier to use; however, users experience more pedal resistance.
Electronic and wireless shifting
Electronic and wireless shifting, as the name implies, is a gear system without wires between the handlebars or gear of the bike. This system was developed to make bikes run smoothly and faster. This system is designed with systems that allow them to calibrate themselves and shift appropriately.
The traditional gearing system is another type of electric bike drivetrain. In this article, we would get to know more about the conventional gearing system divided into the internal gear hub and external derailleur, their pros and cons for bike users, and which is more effective for bikes.
Internal Gear hub
Internal gear hub, abbreviated as IGH, is also referred to as hub gear. This system is used to change the gear ratio of an electric bike. The internal gear hub is enclosed in the rear hub of the bike.
The internal gear hub operates by a planetary epicyclic system. The hub axle of the gear is properly held in place to prevent rotation as it carries torque in every gear except direct drive. The gears are operated using a thumb-pusher, twister, or trigger.
Pros of the internal gear hub
Here are some pros of the internal gear hub:
Low maintenance required
One of the reasons why the internal gear hub is popular is because it requires less maintenance than its counterpart, the derailleur. The gear hub only requires oil changes after every 5000km so that the proper chain tension can be maintained.
Long lasting chains
Another pro of the internal gear hub is that the chains last longer. This is because the chains only run in a straight line and do not run between the gears. This reduces the strain on the chains and makes them last longer.
Riders can shift multiple gears at once
With a gear hub, riders can shift down several gears if they hit a sandy patch or a ditch without much struggle or their chains falling off. This is another good advantage of the internal gear hub.
The internal gear hub is suitable for different road conditions
Electric bikes with an internal gear hub can be ridden in different conditions like muddy or snowy roads without worrying about damage to the gear hub. The gear is completely enclosed to protect it from water or dirt particles.
They are easy to use
Internal gear hubs are easy to use. People with little or no knowledge about bike motors can use electric bikes with gear hubs because they do not require much maintenance and are easy to operate.
Cons of the internal gear hub
Here are some cons of the internal gear hub:
They are costlier
Internal gear hubs are costlier than their external derailleur counterparts. However, the price depends on the model and speed level of the gear.
There are lesser gears
Most modern derailleurs have about 27 gears, but the internal gear hub has only 14 speeds. Many internal gear hubs have between 3 to 11 speeds, but they have larger jumps between gears. Fewer gears may make reaching adequate speed for different terrains difficult.
It is difficult to find replacement parts, especially in developing countries.
Internal gear hubs are intricately designed with modern technology, making finding replacement parts in certain parts of the world difficult. This could be a problem for tourists who intend to use their bikes in remote areas, as they would have to carry spare parts on the journey.
They are slower and less efficient
Internal gear hubs add extra weight to the bike, which makes them slower and less efficient than the derailleurs. Increasing one’s speed would require expending a lot of energy, which can quickly tire riders. This is why professional bike racers use external derailleurs instead of the internal gear hub.
They can only be repaired by the manufacturers
If the internal gear hub of a bike gets damaged, it can not be repaired by the owner or a bike repair shop. It must be taken back to the manufacturer to be repaired. This is because of the complexity of its design and makeup. Tourists with IGH bikes risk not being able to use their bikes if the gear hubs get damaged.
Riders can switch their wheels
Many riders prefer to have different wheels for different terrain, but with an internal gear hub, they can’t switch out the wheels. This is because switching out the wheels is time and energy-consuming and expensive. It would be better to buy a second bike than change the wheels on a bike with an internal gear hub.
Braking and traction might be difficult.
The added weight of the internal gear hub on the bike's rear tire can cause problems with the traction and braking of the bike.
The gears can not shift under load
Shifting the gear under load can damage them; hence, it is advisable to reduce power before attempting to shift the gear.
Rear flat tires can be a nightmare
If the rear tire of an IGH bike goes flat, it could be a nightmare to fix because it may require you to detach the gear hub from the tires and readjust the tension of the chain while repairing it. This is very time-consuming and stressful, which is why tubeless tires or those which puncture protection are advised for bikes with an internal gear hub.
External Derailleurs
An external derailleur is another variable-ratio gearing system for electric bikes. This gearing system comprises several sprockets of varying sizes, a chain, and a mechanism that moves the chain from one sprocket to another.
Modern designs of derailleurs are built with a mobile chain guide that is manually operated using a Bowden cable that is connected to a shifter, positioned on the handlebar, down tube, or handlebar stem. During pedaling, a change in chain tension causes the chain to move or derail from one sprocket to another, hence the name derailleur.
Pros of the external derailleur
Here are some pros of the external derailleur:
They are easy to repair when damaged
Derailleurs are easy to fix and manage with simple bike tools. Any damage to the derailleur can be repaired by a bike repairer anywhere in the world and can easily be self-serviced. Tourists can travel with essential bike tools to fix or overhaul any problems with the bike.
They are easy to service.
The derailleur is not as complex as the internal gear hub and doesn’t require many services and maintenance. Anybody can learn how to service and maintain a derailleur bike, even the bike owners, which can save you constant trips to the bike shop or the money spent for scheduled servicing and overhauling.
They are cheaper
Derailleurs are cheaper to buy and set up. Even low-end internal gear hubs cost more than new mid-range group sets. This is perfect for people on a tight budget.
It is easy to switch out the wheels
With derailleurs, you can easily switch out your wheels. The process is straightforward as opposed to the internal gear hub. This means you can change your bike wheels if you like to use different wheels for different terrains.
Derailleurs have a higher gear range
Many modern derailleurs have a gear range of about 450% to 600%, which gives riders higher top gears and lower low gears. This makes it easier for riders to travel faster across flat roads and even climb steep hills easily.
Derailleurs are lighter and faster
Derailleurs weigh less than internal gear hubs, which makes bikes with derailleurs more efficient and allows them to move faster without the added weight. Riders can opt for lighter derailleur setups if they’re conscious of the weight on their bikes.
Spare parts are readily available
Spare parts for a derailleur setup are readily available and accessible to riders. They can be gotten in almost every part of the world, which makes fixing and repairing them very easy. Damaged derailleurs do not have to be returned to the manufacturers for repairs.
Cons of the derailleur
Here are some cons of the derailleur:
Requires a lot of maintenance
Derailleurs require a lot of maintenance, oiling, cleaning, chain lubing, and the likes of it. Derailleurs need to be maintained every few 100 miles. This can be tiring for long rides as opposed to internal gear hubs that only need to be cleaned after about 5000km.
The chains are not durable
The chains aren’t as durable as they are with internal gear hubs with derailleurs. This is because the chains are always in constant motion, and with every gear shift, the chains move to the side, which keeps them in a sideways motion a lot of the time. This constant motion strains the chains and causes them to wear out faster.
You can’t shift multiple gears at once
Unlike internal gear hubs, the derailleur can't shift multiple gears simultaneously. Attempting to shift several gears simultaneously with a derailleur may cause the chain to drop.
Derailleurs aren’t good for muddy or wet roads
Unlike the internal gear hub that is enclosed and protected from dirt and water, the derailleur is exposed to the elements and can easily get damaged by water and debris, which is why it is unsuitable for snowy, muddy, or sandy roads.
An internal gear hub or a derailleur, which is better?
The question of which is better between the two depends on the bike's purpose or the rider's preference. A racer will be better off with a derailleur because of its speed, lightness, and gear range, while a tourist will be better off with an internal gear hub.
The environment and type of road also play a role in the type of gear system to get for your bike.
Conclusion
In conclusion, when getting a gear system or buying an electric bike, it is best to consider all necessary factors to enable you to make the right choice.
On the other hand, you can opt for a third choice, which is called the hybrid option. The hybrid option combines features of both the internal gear hub and the external derailleur to give riders the best of both worlds.
This gearing system provides the benefits of both types of gearing systems, such as high gear range and better gear spacing ratio. The hybrid gearing system is very common in folding bikes and recumbent bikes.
If you’re having a hard time choosing one of the two, you can consider going for a hybrid gear option.
