Bicycle Drivetrain and Gearing Basics

By : Mr Mamil
Updated :

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Having the correct gearing is a very important aspect of cycling and would definitely make your riding much more enjoyable.

But it’s often overlooked by many as it can quickly become very technical. After all, we all want to ride our bikes and not sweat much over the technicalities behind them.

Understanding the basics behind the gearing would help you make a better-informed decision the next time you think about replacing or upgrading your drivetrain.

There are many factors to consider when choosing the right gearing for your bike, such as terrain, riding style, and fitness level. This guide will help you understand and choose the right bike gearing.

Anatomy of a bicycle drivetrain

A bicycle’s drivetrain is the system that transfers power from the pedals to the wheels. It consists of the chainring, chain, cassette, and front and rear derailleurs.

  • Chainring. The chainring is the large sprockets at the front of the drivetrain. The crank arms are the two rods that connect the pedals to the chainrings. Road bikes have double chainrings (sometimes called 2X). Kids, cyclocross, gravel, and mountain bikes usually have a single chainring (1X). Commuter bikes are likely to have up to triple chainrings (3X).
  • Cassette. The cassette is the cluster of sprockets on the rear wheel’s right side (also called the drive side). Cassettes can have seven to thirteen cogs. More cogs mean a broader range of ears. Each cog can be made up of 9 up to 52 teeth. The more teeth, the lower the gearing is.
  • Chain. The chain connects the chainring and cassette and is the driving force that takes the energy from the pedals and turns it into forwarding motion. The chain is made of steel or aluminum and has holes that fit perfectly into the teeth of the cassette and chainring to avoid slipping.
  • Front derailleur, sometimes referred to as just FD, is attached to the seat tube. It de-rails the chain from one chainring to the other, up and down. A 1X bike will not have a front derailleur.
  • Rear derailleur, known as RD, hangs from the frame via a derailleur hanger from the chainstay. It moves the chain along the cassette, giving you access to a range of high and low gears.
  • Shifters are the mechanism that uses cable tension or electrical signal to make the derailleurs change gear. These days, the shifters are integrated with the brake levers. Shimano calls this STI (Shimano Total Integration).

History of bicycle drivetrains

The first mechanical drivetrains were developed in the 1890s and used a chain connected to a large front sprocket. These drivetrains were not very efficient, requiring the cyclist to pedal at a high cadence to generate enough power to move the chain. In addition, the chains were subject to wear and tear, which limited their lifespan.

In the early 1900s, several inventors began experimenting with ways to improve the efficiency of the bicycle drivetrain. One of the most important innovations was the development of the derailleur, which allowed the chain to be moved from one sprocket to another without having to remove the wheels. This made it possible to change gears while riding, which made pedaling much easier.

The first mass-produced bicycles with derailleurs were introduced in the 1930s, quickly becoming popular with cyclists. Derailleur-equipped bicycles allowed riders to tackle hills and headwinds easily, and they soon became the preferred choice for long-distance touring and racing.

Modern bicycle drivetrains

The modern bicycle drivetrain evolved from early designs that relied on direct human power to move the chain and wheels. Today, most bicycles come equipped with a drivetrain with multiple gears, allowing cyclists to select the optimal gear for any given terrain and situation.

Modern drivetrains are highly efficient, durable, and easy to maintain, making them ideal for everyday riding and competitive cycling.

Mavic, a French company well-known for its wheelsets, was the first to introduce an electronic shifting drivetrain in 1992. Call the Mavic Zap, it, unfortunately, didn’t hit the mainstream market, and the product was eventually abandoned.

It was almost 20 years later that the next electronic shifting drivetrain was introduced.

  • Shimano in 2009, launched its first generation of Di2 (Digital Integrated Intelligence) electronic shifting drivetrain, the Dura-Ace 7970.
  • Campagnolo in 2012, introduced the EPS. 
  • SRAM in 2015 was the last of the three big drivetrain manufacturers to introduce the SRAM eTap, the first commercially available wireless, electronic drivetrain.

Over the past few years, there are many discussions about whether one should get a mechanical or an electronic drivetrain.

So, let’s look at the pros and cons of each.

Mechanical vs electronic drivetrain

Two main types of shifting systems are used on bicycles; mechanical and electronic. Each has its advantages and disadvantages, which should be considered when choosing a bike.

The table below summarizes all you need to know about mechanical vs electronic shifting.

MechanicalElectronic
CostBelow $1,000Above $1,500
MaintenanceCables wear out and need replacementVery minimal except for charging the batteries.
Shifting accuracyDegrades as the cables wear outVery precise shifting
CustomizationNoneButtons are fully customizable to your preferences

Mechanical shifting

Mechanical shifting is the traditional option and uses cables and levers to move the chain between gears. This system is typically less expensive than electronic shifting and is simpler to maintain and repair. However, it can be less precise and may require more frequent adjustments.

  • Cheaper. Mechanical drivetrains are significantly cheaper than electronic gears while providing a smooth shifting experience.
  • Don’t use batteries. Remembering to keep your Di2 battery charged or wait while it charges before you ride is one more complication a rider doesn’t need.
  • Susceptible to cable wear and failure. Over time, the shifter cable will get worn out as it rubs against the cable housing when you shift. Also, as the derailleurs use cable tension to shift, the cable will be stretched. A good practice is to get a new set of cables yearly.
  • Needs constant indexing. As the cable stretches, you’ll need to perform micro-indexing to ensure the derailleurs shift accurately.

Electronic shifting

Electronic shifting uses sensors and motors to move the chain. This system is typically more expensive than mechanical shifting but offers greater precision and easier maintenance.

  • Very smooth and accurate shifting. Electronic shifting is smooth and quiet, and while a well-tuned mechanical groupset can do the same, you don’t want to go back once you try electronic. Once set up, you will probably never need to index the gears again (unless you get a new set of wheels).
  • Self-trimming – The front derailleur on an electronic groupset will automatically align itself to avoid chain rub. It does this by over-shifting to quickly move the chain and then self-trim to compensate for that over-shift.
  • Expensive. They’re not cheap and very often cost at least 2x the price of the equivalent mechanical drivetrain.
  • Batteries. Another battery to maintain and remember to keep charged. While most groupsets will warn you of a flat battery, you need to remember to check before longer rides.

When deciding between a mechanical or electronic shifting system for your bike, it is important to consider your needs and budget.

  • Simple, less expensive option, consider mechanical shifting.
  • Precision and easier maintenance, electronic shifting is the way to go.

How many speeds do you need?

There are a few things to consider when deciding how many gears to have on your bicycle.

  • Terrain. If you’ll be mostly riding on flat, even ground, you won’t need as many gears as someone who will be riding in hilly or mountainous terrain.
  • Speed. If you’re a leisurely rider, you won’t need as many gears as someone who likes to go fast.
  • Type of riding. If you’ll be doing a lot of long-distance riding, you’ll want more gears so you can keep a steady pace and tackle a broader range of terrains.

Ultimately, it’s up to you to decide how many gears you need. If unsure, you can always ask a knowledgeable salesperson at your local bike shop.

11 and 12-speed road bikes

These days, the minimum for road bikes is either 11 or 12-speed. Older bikes (pre-2012) could still be running 10-speed drivetrains.

The difference between 11 and 12-speed is the more the speed, the tighter the gear ratio is.

In other words, there’s a smaller jump between adjacent cogs. It might sound like a trivial matter for some, but it can be significantly felt, especially when riding at your limits. A smaller jump allows you to maintain a more consistent cadence.

The latest Shimano, SRAM, and Campagnolo drivetrains are now all 12-speeds, with electronic shifting.

  • Shimano – Dura Ace R9200, Ultegra R8100 and 105 R7100
  • SRAM – Red AXS, Force AXS, Rival AXS
  • Campagnolo – Super Record EPS

Rather than sweating over 11 or 12-speed, cassette choice is more important, especially for recreational cyclists.

How to choose the ideal cassette size

Cassettes come in many sizes. Understanding what they mean and how they ride helps you greatly with your gearing choices. The numbers on the cassette represent the number of teeth on each cog.

Here’s an example of Shimano’s 11-speed cassettes in its many variants.

  • 11-23T : 11-12-13-14-15-16-17-18-19-21-23
  • 11-25T : 11-12-13-14-15-16-17-19-21-23-25
  • 11-28T : 11-12-13-14-15-17-19-21-23-25-28
  • 11-32T : 11-12-13-14-16-18-20-22-25-28-32
  • 12-25T : 12-13-14-15-16-17-18-19-21-23-25
  • 14-28T : 14-15-16-17-18-19-20-21-23-25-28

For example, an 11-23T cassette has 11T as the highest gear and 23T as the lowest gear. A cassette with a closer gap (eg: 11-23T) will have a tighter ratio (lesser gear jumps) than 11-34T..

The key to deciding the cassette suze depends on the type of riding you do and the terrain.

Here’s a quick way to determine the type of cassette you need.

  • 11-23T or 11-25T. If you ride mostly on flat terrains, you want a cassette with a tighter ratio.
  • 11-28T. If you’re after a versatile all-rounder, this cassette size is very popular among many cyclists.
  • 11-30T. If you ride very hilly terrains, you might want to consider this, or even 11-34T for the steepest hills.

Standard, semi-compact, or compact chainring?

The typical road bike comes with two chainrings (2X) upfront.

For Shimano and Campagnolo drivetrains, they come in one of these setups.

  • Standard – 53/39T. 53 teeth on the big ring and 39 on the small. This is typical for road bikes for stronger or more experienced riders or relatively flat terrain as they are geared for speed.
  • Compact – 50/34T. 50 teeth on the big ring and 34 on the small. This would be suitable for hillier terrains. The smaller rings mean lower gearing, which is suited for long days in the saddle, new cyclists, or hills.
  • Semi-compact – 52/36T. 52 teeth on the big ring and 36 on the small. This is the middle ground, suitable for sportive riders, long days in the saddle, or undulating terrain. The 52/36T sits between the compact and the standard, hence the name.

Finally, there is the TT chainring for flat and fast terrains. It will use either a 54 or 55 and a 39 tooth ring. A larger big ring means a faster top speed and, for the average TT held on relatively flat terrain, helps maintain that speed over the distance.

These aren’t suitable for other types of riding, though, unless you have the power output of Fabian Cancellara or Tony Martin.

SRAM offers different chainring options for its 12-speed drivetrain, as the smallest cog on the cassette has 10 instead of 11 teeth.

  • 50/37T, similar to a standard chainring.
  • 46/33T, similar to a compact chainring.
  • 48/35T, similar to a semi-compact