The Bike Drivetrain Explained

If you’re new to cycling, you might’ve overheard more experienced cyclists chatting about replacing or upgrading parts of their bike’s “drivetrain”.

But what is a bike drivetrain, and what different bike parts does it include?

To help you get to grips with your bicycle drivetrain, we’ll be covering:

  • What Is The Bike Drivetrain
  • Each Of The Drivetrain Bike Parts Explained

Ready for the lowdown on drivetrain bike parts?

Let’s get started!

The Bike Drivetrain Explained: Title Image

What is the bike drivetrain?

The drivetrain of a bike is all the parts involved in converting power from your legs into energy to propel the bike forwards.

In other words, the bike drivetrain is the collection of mechanical parts that make the bike move when you pedal.

The bicycle drivetrain has evolved greatly throughout its history. From the direct-drive simplicity of penny-farthings in the 19th century to the complexity of modern derailleur-based systems, the innovations and progress made in the design of drivetrains have been central to the enduring popularity of the bicycle.

An annotated diagram showing all of the drivetrain bike parts with labels.

Each of the drivetrain bike parts explained

The parts of the bike drivetrain can vary depending on the type of bike (fixies and other single-speed bikes won’t have derailleurs, for example), but the following are all typical drivetrain bike parts found on most geared bicycles:

  • Pedals
  • Crank Arms
  • Chainrings
  • Cassette
  • Front and Rear Derailleurs
  • Bike Chain

Let’s take a look at each of the drivetrain bike parts in more detail.

Photo of black flat pedals against a light grey background.


The pedals provide a contact surface for your legs to rotate the chainset (the name given to the crank arms and chainrings as a unit).

A bike pedal typically consists of a spindle that attaches to the crank arm, the main body of the pedal that the foot sits on, and a set of bearings acting as the interface between them to allow the pedal body to rotate freely.

Bike pedals come in all different shapes and sizes, but most can be broadly split into clipless pedals (especially common on road bikes) and flat pedals (found on BMXs and preferred by some mountain bikers).

Photo of a crank arm against a white background.

Crank Arms

Crank arms – sometimes simply referred to as cranks – are the levers that connect the pedals to the chainrings.

Like wheels and frames, crank arms come in a range of sizes. Longer crank arms provide greater leverage, amplifying your pedaling force, but require more torque to turn (similar to using a bigger gear) and put extra stress on the joints.

Most manufacturers consider 170-175 mm to be the “Goldilocks Zone” of crank arm length, providing a compromise between leverage, ground clearance, and joint stress – although particularly tall or short cyclists might want to experiment with crank lengths outside of that range.

Close-up shot of a metal chainring against a white background.


The chainring is the toothed metal disc that transfers power from the pedals to the rear wheel via the chain.

When a bike has multiple chainrings, they act as the front set of gears. The front derailleur moves the chain between the different chainrings to make pedaling easier or harder. The larger the chainring, the harder it is to pedal, and the further each rotation will propel you forward.

Though the standard for road bikes is to have a dual-chainring setup (and sometimes even a 3x chainring system), single chainrings are becoming increasingly common for mountain bikes. A single chainring helps shed weight and reduce mechanical complexity, while still allowing for a broad range of gear ratios when paired with a wide-range cassette.

Photo of an upright bike cassette against a white background.


The cassette is the component that contains the rear set of gears. It’s connected to the hub of the rear wheel – when the chain turns the cassette, the cassette turns the wheel.

The cassette began to appear in the 1970s as an evolution of the old freewheel (also known as a block) mechanism. Since then they’ve become more popular and cheaper to produce, and are now the standard for bikes with derailleur-based drivetrains.

Cassettes typically contain between 5 and 12 sprockets (the name for each gear ring).

Close-up of a silver front derailleur on a black bike.

Front Derailleur

Derailleurs are devices that “de-rail” the chain from one sprocket or chainring to another, allowing the rider to change gear.

Rudimentary derailleur systems have existed since the 19th century, but only came to prominence in the 1930s.

Frustrated by the existing process of changing gears (which involved removing the rear wheel and flipping it over to a differently-sized sprocket on the other side), bike racer Tullio Campagnolo designed an innovative new road-actuated derailleur system that would allow the rider to change gears without getting off the bike: the Cambio Corsa.

The derailleur’s design soon evolved to be cable-actuated so that cyclists no longer had to reach back to the seat stays to change gear. This helped the derailleur system become much more popular, and by the 1950s they were commonplace.

Friction shifters remained the norm until the introduction of indexed gears by Shimano in 1985. Indexed gears meant that the derailleur would move to a pre-determined position for each gear, improving precision and ease of use. Indexed gears are now standard on almost all geared bikes – so they’re probably what you’re already used to using!

The front derailleur is responsible for moving the chain between the different chainrings. A bike drivetrain will only feature a front derailleur if it has multiple chainrings.

Photo of a rear bike derailleur against a grey background.

Rear Derailleur

The rear derailleur serves the same purpose as the front derailleur, but moves the chain between the sprockets of the cassette on the back wheel instead.

Additionally, the rear derailleur is also responsible for maintaining tension in the chain (pulling it tight to remove slack).

It achieves this with a pair of pulleys. The upper pulley – called the “guide pulley” – is responsible for guiding the chain onto its intended sprocket. The lower pulley – called the “tension pulley” – is spring-loaded. This allows it to pull backward on the chain, keeping it taught regardless of the gear ration being used.

Close-up shot of a silver bike chain.

Bike Chain

The bike’s chain is the final piece in the bike drivetrain that allows all the other components to work together.

The chain is responsible for transferring energy from the chainset to the sprocket, providing power to the rear wheel.

The chain is made up of individual links that hook onto the teeth of the chainrings and cassette sprockets. Chains of different widths are compatible with different cassette ranges: cassettes with more sprockets (e.g. a 12-speed cassette) require narrower chains, and vice versa.

Found this article on Drivetrain Bike Parts helpful? Check out more from the BikeTips experts below!

Photo of author
A road cyclist at heart, Rory clocked early on that he had much more of a knack for writing about bikes than he ever did racing them. In recent years, the focus of Rory's love affair with cycling has shifted to bikepacking - a discipline he found well-suited to his "enthusiasm-over-talent" approach. Originally hailing from the United Kingdom, Rory is currently based in Buenos Aires, where he is loving taking advantage of all the backcountry bikepacking South America has to offer. Rory is a UESCA-certified cycling coach.

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