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Electric Bike Gearing System Guide

Electric Bike Gearing System Guide

Electric Bike Gearing

Confused about the pros and cons of derailleurs, hub gears, and CVTs? We demystify it all below. A lot of e-bike hype focuses on the performance of the motor or the size of the battery. One area that is often overlooked is electric bike gearing.

Surely you will get the same options as a normal bike? Just to a point; the e-bike revolution has brought many meanings to e-bike design, one of which is the expansion of available gearing options.

With the extra motor power, larger, better-performing gears can be used that are too heavy or difficult to pedal for most non-e-bike riders. These are described in the Advanced Systems section below.

But for now, let’s stick with gear system 101: derailleurs and hub gears

The Basics: Transmissions and Hub Gears

Most e-bikes are equipped with derailleur gears, with hub gears being the main alternative. Both options go back decades, so both are very technologically advanced and should work well for their intended purpose. But what are they and what are the pros and cons of each system?

Transmission Gears: An Overview

Derailleur gear units are so named because they always consist of a black derailleur (or rear mechanism) and a rear cassette (or rear gear), which is a row of silver chainrings. Some bikes also use front derailleurs (see photo below), but front derailleurs are very rare on e-bikes.

The derailleur gears are external, and the rear derailleur is usually connected to a cable. Tightening the cable through the shifter on the handlebar means the derailleur guides the chain up over the chainrings to a larger, easier to pedal gear (low gear), perfect for hill climbing. Releasing the tension in the cable means the spring in the derailleur pulls the chain down and out onto the smaller, harder-to-pedal sprockets (higher gears) for high speeds.

Terminology for Common Components on a Derailleur System

Common derailleur gear manufacturers on e-bikes are Shimano and SRAM.

Advantages of transmission gears:

They are lightweight systems that are cheap to replace if damaged in a market with a limited budget.
Said to be more efficient than internal hub gears.
The derailleur offers a wide selection of gears (i.e. very low gears for easy hill climbs and high gears for speed on flats and downhills).
To add more color to the last point: In recent decades, a relatively simple form of wide-range gearing has been developed, using only a single sprocket on the front of the chain and a very wide range of gears on the rear cassette.

Electric Bike Gearing 
1 x 12 wide range derailleur gears from Shimano – in this case on the high performance, sporty Cube eMTB

The number of teeth is usually given in the transmission gear specification. For example, in a high-quality mountain bike setup, you might see something like “Front Chainring 36T Rear Cassette 11-50T” – where the T is the number of teeth.

This setup means “low gear ratios” – i.e. easy pedaling on more drag-resistant off-road surfaces, and you need to tackle very steep terrain.

Note that the fewer teeth on the front sprocket, the easier the bike is to pedal, and a large cog sprocket in the rear derailleur means easier pedaling.

By contrast, a typical city bike might have a gear setup with a 40T front sprocket and 11-34T rear cassette, providing a narrower, higher gear range for typical town riding conditions.

Disadvantages of Transmission Gears

Shifting gears at a standstill or shifting multiple gears at once is not recommended.
Open to elements that get dirty easily, thus becoming noisy and difficult to move.
Due to their open design, they require regular cleaning and maintenance.

Sticking out near the ground like they do, the derailleur is also prone to damage, although it usually takes a fairly severe shock to cause damage, so it certainly shouldn’t happen that often.

Having said all that, compared to hub gears, they are relatively easy to maintain for the user.

Hub Gears: An Overview

The hub gear is fully housed in the rear hub. The Shimano Nexus series pictured above is available in 3, 4, 5, 7, 8 and 11 speed options. 8-speed is probably the most common choice on electric bikes. You may also see hub gears abbreviated as IGH (Internally Geared Hub).

In terms of number of gears, the Rohloff system is the granddaddy of all hub gear systems with 14 gears, but be aware that it is very heavy and very expensive. It does feature in many e-bikes everywhere, including many in the Riese & Muller line, proving that there’s no real reason why the proper hub gear couldn’t be fitted to just about any type of e-bike.

Rohloff hub gear with belt drive

Like derailleurs, hub gears have distinct pros and cons.

Advantages of hub gears:

Low maintenance. Since the gears aren’t exposed to the elements, they can often travel thousands of miles without much attention. Your chain should also last longer because it doesn’t constantly move between the different gears.
Can shift multiple gears at once while stationary – ideal feature for start-stop riding around town
If you’re looking for a belt-driven e-bike instead of a chain-driven e-bike, you’re going to need a hub-gear bike, as the derailleur doesn’t work with belt drive.
Great for riding in all conditions as they are sealed to the elements.
Disadvantages of hub gears:

Usually heavier and more expensive than derailleur gears, especially for systems with more gears.
If something does go wrong inside the hub, that’s usually the job of an expert (although this is very rare, and reliability, on the other hand, is often a reason to choose hub gears).
You can opt for “rear pedal” coasters or fully enclosed drum brakes with some hub gears, although these options are more common in continental Europe than in the UK and US.
Usually less range than a wide range derailleur system, but be aware that Shimano’s 11-speed setting and Rohloff’s 14-speed hub gear will approach or exceed many derailleur gear settings in the range they offer.
The rear wheel can be more difficult to remove (for tread repair, maintenance, etc.) than a derailleur system.

Which is better: a derailleur or a hub gear system?
The internet is full of debates about which is better – derailleur or hub gear.

The answer is simple: it depends. It depends on how you ride and what derailleur or hub gear the e-bike runs on.

As a very general rule, hub gears and cheaper narrow-range derailleurs are used for city bikes, while derailleur gears are used for more sport-oriented e-bikes, i.e. electric road bikes or off-road bikes.

Here is a helpful review video on derailleurs and hub gears.
Electric Bike Gearing

Advanced Electric Bike Drivetrain

Electronic shifting was first introduced to allow road riders to get perfect, precise shifts on the derailleur gear system to make their road bikes run as smoothly as possible while shifting, and therefore as fast as possible.

Essentially, there is no cable between your handlebar and gear as you would on a traditional system, and a small motor change makes a difference. On a manual system, this is done when you push a button on the handlebar, sending the electronics over a wire (or wirelessly) to a control on the gear.

Since these systems have sensors built into them, they claim to provide more precise shifting and be able to calibrate themselves; traditional gear systems can suffer from cable stretches, bumps, and bumps, and just wear out, meaning the gears sometimes You don’t want them bouncing between them, or simply not being able to change the handlebars while you make the gears.

Usually a little maintenance fixes these issues, but electronic replacement claims this shouldn’t happen.

Since this is a relatively new technology, it will take a while for motor manufacturers such as Bosch and gear manufacturers such as Shimano to integrate the latest motor systems with the latest electronic gears.

Here’s a pictorial demonstration of how Shimano’s electronic Di2 system works with a Bosch mid-mount motor. If you’re interested in this system, we recommend an extended test drive to see if it suits your riding style.

Bosch mid-drives also work with Rohloff and Enviolo (see below) electronically shifted hub gears.

Continuously Variable Transmissions (CVTs): An Overview

The large rear hub recognizes the CVT gear system. This one has a large automatic shifter.

CVT is a long sentence for a very simple concept – there is no fixed number of gears on a CVT system, instead when you turn the handle or push a button, the gears just move up and down the range – it’s impossible to stall And let the pedals spin like crazy, which can happen on traditional systems (especially hub gears) because the system is always in gear.

Of course, as with any cycling technology, there are pros and cons:

Advantages of CVT:

EASY TO USE – Just turn the torque handle or press a button on the handlebar control to choose how hard or easy you want your e-bike to pedal. That’s it!
low maintenance
There’s an automatic option, which means you don’t even have to move the handle or press a button, and the system will shift gears for you.

Disadvantages of CVT:

Relatively heavy, and certainly has more pedal resistance than other gear systems.
more expensive than other options

Remember that e-bikes are suitable for this type of gearing, as the motor power means you won’t notice the extra drag. However, this means your battery range will be reduced a bit, as the electric assist system has to work harder to overcome the extra drag.

Again, a mid drive from Bosch will be connected to this system:

Bottom axle drive: overview

It is also possible to place the transmission around the pedal shaft. Obviously, this doesn’t apply to the mid-drive as that’s where the motor is, but bottom bracket gear specialist Pinion has come up with this very sophisticated looking system that works with the rear hub motor.

The main advantage of this system is that the motor power does not pass through the gears, thus reducing gear wear and stress. Like other closed gear systems, it adds weight and may not be as efficient as a derailleur system.

German company Tout Terrain specializes in this gear and motor setup, and it looks pretty solid and reliable for a “workhorse” type e-bike task.

So how many gears does your e-bike gear system need?
After we’ve said all this, don’t get too hung up on what gears are needed – increasing the motor power actually makes having lots of tightly spaced gears (such as those found on traditional road racers) less important. EBR boils it down to these four points.

The easier your terrain is – whether it’s rolling off hills or ground – the less gear you’ll need. For flat city riding, you might even want to consider the ultimate in simplicity and low maintenance: a single-speed electric bike.
For steep trail rides on challenging terrain, choose a lot of gears and make sure they have a wide range. Gear range – the difference between the lowest and highest gear – usually expressed as a percentage. Over 500% can be considered a very wide gear range and an average of around 300%, and should enable you to tackle quite a bit of terrain.
Hub gears are best for low-maintenance “utility” style riding where the weight of the e-bike is less of a concern. As athletic performance and light weight become more important, you may be inclined to use a derailleur setup (although be aware of the Rohloff on some off-road e-bikes). Hub gearing may also be easier and more intuitive for e-bike newbies.
Of all the so-called “advanced systems” covered above, the Enviolo CVT is probably the best one for absolute e-bike newbies, as it is very easy to use, while the electronic shifting option can be considered a low maintenance and sporty option, depending on specific settings. Automatic transmissions are still an emerging technology, so EBR strongly recommends test-riding one of these systems before buying to check if it really works for you.

If you are looking for a new way of commuting or want a healthier lifestyle, we are here to help you. Visit our website to learn more about electric bikes and electric scooter or please leave information to us.