The Drivetrain is the main mechanism of the bike.
The Drivetrain is composed of the shifters, crankset, cassette/cogs, chain, front derailleur, rear derailleur and brakes. The big names of drivetrain manufacturers are Shimano, Sram and Campagnolo. These companies have different series for their components. Having all components from the same series is called having a "Groupset" or a "Gruppo". Although one can mix and match different components from different groupsets or different brands, there may be occasions where these would not be compatible.
The Shifters are the main controls for the bicycle's mechanism. This allows the rider to shift to a heavier or a lighter gear as is needed. When climbing up, a lighter gear is necessary. When riding a flat stretch or going downhill, a heavier gear is needed. Almost all mountain bikes have the shifters and brake levers that are separate. For most road bikes, the shifters and brake levers are combined together - "brifters" (brake + shifter).
The shifters and brake levers on a road bike.
The Crankset is the next component. This is the start of the mechanical process for propelling the bike. It is comprised of the Crank (the "lever" we pedal) and the Chainring (the actual teethed wheels that engage the chain). The chainrings' sizes are counted by the number of teeth. Larger chainrings are harder to pedal and are for flat areas. Smaller chainrings are easier and more suited for climbing. Chainring sizes are typically written by listing all the chainring sizes separated by a slash. Examples are 50/34, 53/39, 42/32/24, etc. Cranksets can range from having only one chainring up to three - single, double and triple. Mountain bikes usually have triples but double and single chainring setups are becoming more commonplace. Road bikes usually have doubles. A handful have triples and an even fewer crowd have single chainrings.
An example of a double crankset on a road bike.
A triple crankset on a cyclocross bike.
The Cassette is the counterpart of the chainrings on the back. Likewise, the sizes are determined by the number of teeth. Sizes are usually written as the size of the smallest and biggest cogs. Examples are 11-25, 12-27, 11-32, etc. Unlike the chainrings where bigger is heavier, the opposite is true for the cassette. Bigger cogs/sprockets are easier to pedal compared to smaller ones. Also, it is common to hear terms like 9-speed, 10-speed, 11-speed, etc. This simply refers to the number of cogs or sprockets at the back.
An example of a cassette.
The Derailleurs are the mechanisms responsible in changing gears. These traditionally connect to the shifters via cables but modern technology allowed for electronic and even wireless shifting. These mechanisms derail the chain from the chainring or cog to the next. This allows the rider to alter the load they are pedaling when riding. The front derailleur handles the changes in chainrings. The rear derailleur hands the changes in sprockets/cogs.
The front derailleur changes the chainrings at the front.
The rear derailleur changes the rear cogs engaged by the chain.
The most important part of a drivetrain are the Brakes. For stopping, for safety, for your life and limb. Brakes can be divided into Rim and Disc. The difference is where the brakes apply stopping force. Rim brakes apply force on the rims to make the wheels stop. On the other hand, disc brakes apply force on a disc or "rotor" attached to the hub of the wheel to make it stop.
A Rim brake on a road bike.
An example of a Disc brake.
This concludes the article on the bike's drivetrain. Can you check your bike? What kind of crankset do you have - single, double or triple? What kind of brakes do you have? What is the range of your bike's cassette? How many speeds or cogs are there? We hope we helped you identify what your bike has and maybe gave you an idea on what you need.
Please stay tuned for Part 5 - The Cockpit.
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Links to previous Parts of this series.
Part 1 - What is a Bicycle?
Part 2 - The Frame
Part 3 - The Wheels
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