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What is a Sprocket on a Bike? – A Bike Sprocket Guide

Written by Gary Johnson / Fact checked by Henry Speciale

what is a sprocket on a bike

Some might think that wheels are the most essential components of a bicycle. But a bicycle wheel will not function without a pedaling system, including the sprocket and the chain. These two work hand in hand to enable the mechanical movement of your bike.

However, between a chain and a sprocket, we are more familiar with the bike chain than a sprocket. So, what is a sprocket on a bike?

A sprocket is a mechanical wheel that comes with teeth or tiny notches and normally rotates along the chain. To know more about a sprocket, read this detailed guide below:

What to Know About a Sprocket? Sprocket Meaning

A bike sprocket is typically a metal object that transmits motion from the bike pedal to the chain and wheels. It is a common component among motorcycles, tracked vehicles, and bicycles which require a chain to function completely.

Pedal shafts in a bicycle come with a big sprocket wheel. This wheel comes with teeth that can accommodate the length of your bike chain. The sprocket helps rotate the chain and enforce motion to a small sprocket for the rear wheel to move.

Since sprockets are a common component among automobiles, it also comes in various sprocket size, sprocket design, and the number of teeth.

In a regular bicycle, the standard diameter of a sprocket that you will notice is around 12mm. This diameter also comes with 11 to 12 teeth. On the other hand, for larger bikes, the sprocket can have teeth from 21 up to 32.

Measuring Sprocket


  • Teeth

The number one noticeable sprocket parts are the teeth.

Bike sprockets come with a number of sprocket teeth which engages the chain while moving. This is one of the easiest ways to measure sprocket.

For a regular road bike, the teeth can range from 11 to 12. The number of teeth also varies as the BMX sprocket has 25 – 28 teeth, while most MTB has 32 – 34 teeth.

  • Pitch Diameter


This measurement refers to the circumference of your bike sprocket. The measurement starts from the middle of one roller chain pin to the midpoint of the next roller chain pin about 180 degrees.

  • Pitch


This involves the measurement of each tooth of the sprocket. It is normally measured in inches and should always be in equal fitting to the pins on your bike chain.

  • Outside diameter


Another measurement you should know is the sprocket’s outside diameter. The circumference around the sprocket involves the tips of the sprocket’s teeth.

You will notice that there are two standard size chart for sprockets today, and they are used for sprocket identification. They are the ANSI and the British Standard.

ANSI standard caters to North American and Asian sprocket manufacturers, while the ISO is for European and African nations.

British Standard (BS) 04B 05B 06B 08B 10B 12B 16B 20B 24B 28B        
American Standard (ANSI) 25 35 41 40 50 60 80 100 120 140 160 180 200 240

Types of Sprocket


Using a sprocket nomenclature, you will find that sprockets are classified as Type A, Type B, Type C, and Type D. The different types of sprockets are designated with letters and classified based on the chain size, bore size, and tooth count.

  • Type A

This type of sprocket is flat and lacks a hub on it. It is the most basic roller chain type with a very minimal plain bore. The sprockets are also termed the “plate sprockets”. It is plain and has no added thickness that is normally attached to the flanges or hubs of your bicycle.

  • Type B

Unlike a Type A sprocket, a Type B sprocket comes with an extended hub on one of its sides. It also goes with a plain bore or finished bore wherein you will find a keyway and two set screws.

For this type, the first setscrew is found above the keyway, while the second one is around 90 degrees away from the keyway. Since it has a hub, you can easily fit it onto the bicycle, and it lessens the bulkiness of the bearings of your equipment.

  • Type C

A Type C sprocket is a more elevated type of sprocket since it has two hubs on both sides of the plate. It is typically attached to a driven sprocket and requires a bigger pitch diameter. The hubs come in various sizes depending on the load or weight needed to support them.

  • Type D

A type D sprocket is the most complex type of bicycle sprocket. It comes with two hubs, but every hub has a different thickness, so it looks asymmetrical on the outside.

How Do Sprockets Work?

Sprockets on a wheel always work with a chain or a belt. A typical bike has two sprockets and is connected by a chain. The first sprocket is the driver sprocket, while the other is the driven sprocket.

The chain-sprocket system creates movement based on the rider’s foot motion or pedaling. For the sprocket to work, you need motion or force from the rider.

The energy from the biker will be transmitted through the chain or the power transmission chain. It will start from the first sprocket to the bike chain until it reaches the second sprocket.

The sprockets’ efficiency in a bicycle depends on the ratio between the front and rear sprockets. You will notice that the teeth numbers in the front and rear sprocket are different. This affects your speed and acceleration when riding.

If you have a bigger rear sprocket bicycle with more teeth than the front sprocket, you will increase your acceleration but eventually lessen your top speed. This is the opposite of having a smaller rear sprocket but a bigger front sprocket that can significantly decrease your acceleration but heighten your top speed.



What’s the difference between a gear and a sprocket?

Sprocket vs gear may look very identical, but they function differently.

  • As mentioned earlier, a sprocket comes with teeth interlocked with a chain or belt. It is specifically designed to work with a belt or chain and not another sprocket.
  • On the other hand, a gear also comes with teeth engineered to interlock with another gear. The teeth in a gear work and connect directly to another gear, facilitating rotational movement. Sprocket look like gear but considerably vary in their functionality.

What sprocket is best for top speed?

Getting a top speed with your bicycle greatly depends on the ratio between the front sprocket and the rear sprocket.

To get a top end and faster top speed, you need to use a bigger front sprocket combined with a smaller rear sprocket.

For an MTB, getting a sprocket with 32 teeth will get a top speed.


Speed and acceleration in a bicycle are not only affected by how fast a rider pedals, the terrain, or the amount of energy exerted. It also depends on the gearing system and other components, specifically sprockets and chain.

So, it is important to know what is a sprocket on a bike.

Sprockets in a bicycle play a critical role in your speed and acceleration. You can increase your acceleration or obtain your top speed depending on the rear and front sprocket ratio.

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