Bike Drivetrain Parts – What You Need Know

Ever wondered what propels your bike forward and why the bike moves forward when you put pressure on the pedals? The drivetrain is responsible for making the bike move forward and it features a varying set of components that enables you to push the bike forward in different directions and have some success doing so.

When looking at your bike, you will see a chain that often connects the front of the bike to the rear wheel. When you pedal, the pedals push the chain forward, which creates momentum. The momentum is exerted on the rear tire, which enables you to push the bike forward and keep you in control of the overall speed.

Bicycle drivetrains are intricate concepts and they might not be easy for everyone to understand. However, your bike will not be able to move forward if you don’t have a drivetrain that can propel it. The main purpose of this article is to help you better understand the drivetrain and enable you to propel your bike forward.

The Evolution Of The Bicycle Drivetrain

The drivetrain started as a far more complex system than we know nowadays. It started by having derailleurs at the front and rear of the bike. Instead of having a single chainring, these cassettes feature two or even three chainrings. The result was that drivers would have numerous gear combinations to work with. With so many gears, it was dubbed to be high gears and low gears:

  • High Gears: The high gears consist of a large gear in the front and a smaller gear at the back. The design aimed to create tension in the pedals when going downhill. The chain would be slow-moving over the large gear, creating resistance and reducing speed downhill.
  • Low Gears: The lower gear option is the opposite and features a large gear at the rear and a smaller gear at the front. It would reduce the resistance, which makes pedaling easier and should be better for climbing.

While the design and multiple gears would be beneficial to riders when compared to single-speed bikes, it would also be a cumbersome setup. Maintenance on the bike would not only be more tedious but also more expensive. Riders also kept running the risk of the chain slipping off the bike and costing them in competitions.

The Modern Change

In the modern era, bicycle drivetrains have evolved to having only one chainring at the front. Bike developers have found that larger cassettes can be installed at the rear of the bike, which gives them the range of carrying all the different gears. A single 34T or 36T ring would be mounted to the front of the bike.

A 10 – 12-speed cassette can often be mounted to the rear of the bike, which makes it easier to have some versatility. For example, a cassette with 11-46T or 10-50T rings would provide the ideal gear range. You can view it in the same sense as a conical design, with the largest gears at the front and the smaller gears at the rear that work from large to small.

The modern design is much better and it does not have as much maintenance that needs to be done. You can find that maintenance is limited and when cleaning the drivetrain, it should be that much easier to get it in peak condition. It also means that the risk of the chain falling off the drivetrain only relates to the rear of the bike.

Different Components Of The Drivetrain Explained

With so many components, it can be hard for some beginners and those with an untrained eye to forget about what each of them means. This section aims to show you the different components of the drivetrain and allow you to better understand it. Here is a basic understanding of the different components that comprise the bicycle drivetrain:


Cassettes are located at the rear of the bike and they generally connect to the rear tire. These can be viewed as the interface of the drivetrain and they are set up in a conical shape. The purpose is to make it easier when shifting and to ensure that the shifting process is fluid. Cassettes typically have 8/9/10/11-speed designs.

The cassette might seem pretty straightforward, but there is plenty of planning and design that goes into the cassette. Not only do the cogs need to be perfect, but the chain used needs to fit these cogs. You cannot use the wrong chain with the wrong cogs, as the cogs will not gel with the chain and allow it to move freely.

The cassette is the main part of the bike that enables the user to shift between different speeds and make it possible to have the right resistance for their bike at the right time. It might not be easy every time to fix any damages, but you want to have a fluid cassette and chain combination to complement your ride.


When it comes to the most important components on the bicycle, the chain is probably one of the components you need to make sure works. The purpose of the chain is to transfer the power exerted onto the pedals to the rear hub. The rear hub turns the rear wheel, which propels the bike forward and gives you momentum.

Roller chins with a width a chain pitch of ½ inch are commonly used on modern bicycles. The chain pitch is the distance from roller to roller, while the width is measured between the chainplates on the chain. The chain width will vary from bike to bike and manufacturer to manufacturer to accommodate their setup.

Keep in mind that the width of the chain needs to get smaller with the more sprockets the bike has. Having more sprockets means that you will need a thin chain to provide clearance and not to interfere with the rest of the cassette. Having a professional assist you with these kinds of setups is often the best way.

Read more about Bike Chain


The crankset is another major component of the bike and it connects the chainring. The crank is connected to the bottom of the pedals and it should be secured to the axis that runs through the chainring. Once you put pressure on the pedals, the crank will turn the chainring, which transfers the energy to the rear of the tire to create forward motion.

Cranksets are also different depending on the bike. Aside from being made from different materials, the length varies depending on the bike size and the rider. However, cranksets are often made from aluminum. Cheaper cranks can be made from steel, with the high-end options being made from carbon fiber.


The pedal is the one component that even the beginner will understand and it is designed to ensure the rider has a mechanism to transfer the energy from the front of the bike to the rear and propel the bike forward. Pedals can also range in size and different types of pedals make a difference depending on the bike.

Pedals on entry-level bikes are often basic and made from steel. They should comfortably fit the feet of the rider and allow them to have comfort when pedaling. However, high-end pedals often need the right shoes and they will clip into the pedals to give the rider more consistency and reduce the risk of miss pedaling.

The pedal will connect to the crank, which connects to the chainring and the combination of these three components are what ultimately propels the bike forward and makes it possible to ride from one location to the other.


The derailleur is the smaller component that people often do not give enough credit for. However, the purpose of the derailleur is to shift the chain from one chainring to the next. However, the derailleurs vary depending on the bike. There is also a significant difference between the front and rear derailleur when it comes to performance:

  • Front Derailleur: The front derailleur will be measured in terms of speed compatibility and it should vary depending on the chainrings located at the front of the bike. The purpose is to move the chain from the larger chainring to some of the smaller chainrings. However, it should also be able to lift the chain back up to the larger rings. Your derailleur must accommodate the number of teeth on the largest chainring, which is referred to as the cage diameter.
  • Rear Derailleur: The rear derailleur is slightly more complex and while it should be able to do the same as the front derailleur, it also needs to deal with excess chain. When shifting from a large chainring to a smaller one, you have an excess chain that is not needed to make a full revolution. The rear derailleur features a component that retracts the excess chain to create a smooth motion.

Bottom Bracket

When focusing on the crank, you will also get to see the bottom bracket. The purpose of the bottom bracket is to connect to the crank. Inside the bottom bracket, you traditionally have ball bearings, around which the axle rotates and propels the bike forward. It enables the chain to push the bike forward when you are pedaling.

The bottom bracket will vary from brand to brand and some of the modern manufacturers have designed bottom brackets that do not feature any axle. The axle is often built into the crank and rotates around the bearings. Depending on the brand, the diameter of the bearings will also vary and have an impact on the performance.

We have also noticed that the bottom bracket varies from country to country, with bikes being designed in different parts of the world having different bottom brackets. As each company and bike manufacturer tries to lay their claim for being the best brand on the market today, you should notice multiple changes in the future.


The chainring is another interesting component and we have mentioned it numerous times during the article. The chainring is a ring with cogs on the ring that accommodate the chain. These cogs need to be designed with precision and they will need to be functional to ensure that the chain remains on the bike.

Aside from the diameter and cogs on the chainring, it also varies depending on 8/9/10/11-speed bikes. Most chainrings are made from aluminum, but like many of the other components, they can often vary. Some of the high-end bikes have carbon fiber chainrings, but aluminum is often the best material for those starting.

When looking at the chainring, you will find that the chain fits the bike perfectly. If the chain does not fit perfectly onto the bike, it could be a concern for the rider. No one wants to deal with a chain that slips off the bike while they are riding. Not only is it dangerous, but in competition situations, it could cost you the race.


The bicycle drivetrain is one of the most important parts of the bike. However, not all bikes are similar and drivetrains vary. While they might look similar on television, they are designed for specific riders with specific features. If you are looking to replace your drivetrain or you want to buy a new bike, you should get to grips with the drivetrain and make sure you understand the components.

Learn more about Bike Parts Diagram

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