How Bicycle Gears Work

If you’re new to cycling (or even if you’ve been biking for a while but tend to zone out when too many numbers become involved), bike gears can be intimidating. The gears themselves can be hard enough to figure out. Terms like “gear inches” or “cross chaining” might as well be in another language.

Once you have a little background knowledge, though, understanding how gears work can make your cycling experience much more enjoyable. Below, you’ll find everything you need to know about bike gears explained.

What are gears on a bike?

Every bike is made up of a drivetrain: the set of gears and chains used to keep your bike moving smoothly. We’ll begin first with a basic overview of the front gears.

Front gears

The chainring

Chainrings, or sprockets, are the gears at the front of the bike. Chainrings are ordered in ascending size, with the smallest chainring sitting closest to the frame of the bike.

Chainrings at the front of a bike.
Chainrings at the front of a bike. In this image, the smaller, inner chainrings are partly obscured by the large outermost chainring. (© Pedal Street)

The chainring dictates both how quickly your bike travels and how easy it is to pedal. Switching to a smaller chainring results in easier pedaling but slower speeds, while using a larger chainring makes it harder to pedal, but will let you travel more quickly.

Some bikes (called singles or 1x) might only have a single chainring. Most bikes, however, will have either two or three chainrings (known as doubles/2x or triples/3x, respectively), thus allowing for a greater variety of gears.

Chainrings are typically round, but since the 1990s some cyclists have been taking advantage of oval chainrings.

The front derailleur

If a bike has more than one chainring, it needs a front derailleur. The purpose of a derailleur is to move a bike’s chain from one chainring to the next.

Front derailleur on a bike
The front derailleur. Its job is to move the chain between rings. (© Pedal Street)

The front derailleur is located near the bike pedals and is mounted with a bracket or clamp against the frame of the bicycle. The bike chain first runs through the cage of the derailleur and is then sent through the chainrings. When changing gears, the front derailleur will move the cage outward or inward, thus pushing the chain from one chainring to the next.

Rear gears

The cassette

Rear cassette on a bike
The rear cassette. If you count the cogs, you can see this one has 10. (© Pedal Street)

Your bike’s cassette, also called a cogset, is the set of gears (cogs) mounted on the rear of the bike on the right-hand side of the rear wheel. The cassette on most modern bikes typically contains between eight and 11 cogs, each consisting of 11 to 28 teeth. The largest cog is mounted closest to the wheel, and outer cogs are placed in order of descending size. Larger cogs equate to slower speeds and easier pedaling, and vice versa.

The rear derailleur

Rear derailleur on a bike
The rear derailleur does a little more work than the front. (© Pedal Street)

Like the front derailleur, the rear derailleur is the mechanism used to shift the chain from one cog up or down to the next one. However, the rear derailleur also has two other functions: It picks up the slack when moving between large and smaller gears, and it maintains the level of tension needed to keep your chain on the chainrings.

How to use bike gears

Once you have a basic understanding of the gears and components that make up your bike’s drivetrain, you can start digging into the numerical stuff.

Bike gear ratios explained

The gear ratio refers to how many times the back wheel of a bike will rotate for each complete revolution of the pedal. In other words, if the rear wheel turns once when you turn the pedals once, the bike has a gear ratio of 1:1. If the rear wheel completes three turns for every turn of the pedals, the bike has a gear ratio of 3:1.

For a more in-depth understanding, let’s dive in.

What are gear inches?

Gear inches is the unit we use to describe how far a bike will move forward with each rotation of the pedal. Contrary to popular belief, calculating your gear inches won’t actually give you the exact number of inches your own bike moves after each stroke of the pedal—you’ll need to calculate your meters of development in order to find that measurement. Instead, gear inches are a standardized unit of measurement used to compare one type of drivetrain with another.

To calculate gear inches, first divide the number of teeth in the front chainring by the number of teeth in the rear cog. Then multiply the quotient by the drive wheel diameter in inches. This gear inch calculator will make the math easier.

As a general rule, the lower a gear inch range, the easier it is to pedal.

What is gear range?

The gear range is a number used to refer to the difference between the lowest available gear on a bike and the highest. In other words, look at the largest sprocket on your bike (for example, a 28-tooth sprocket), divide it by the smallest one (for example, an 11-tooth sprocket), and then multiply the quotient by 100 in order to find the percentage. In the example above, the gear range would be about 255 per cent (28/11 multiplied by 100), indicating that each pedal stroke in the highest gear would allow you to travel 2.55 times as far forward as pedaling in the lowest gear.

When to shift

Each time your terrain, direction, or wind conditions change, you’ll likely have to choose whether or not to shift to another gear. If you’re climbing up a hill, about to make a sharp turn, or riding directly into a strong wind, you’ll probably want to shift into a lower gear. Low gears are “easier” and allow you to pedal with less resistance. If you’re instead biking downhill or with the wind at your back, use a higher gear to create more resistance.

Always try to shift before you have to; shifting gears is much easier before you get to a hill than trying to do it after you’ve already started climbing.

Cross-chaining

If your bike has a double or triple crankset (ie. more than one chainring), you might occasionally find yourself using a combination of gear difficulties; for example, using the smallest cog (the hardest gear) in the rear while also using the smallest chainring (the easiest gear) in the front. This is called cross-chaining, and as a general rule, you’ll want to avoid it as much as possible.

Cross-chaining bike gears
This is cross-chaining. You’re on the innermost (easiest) gear at the front and the outermost (hardest) gear at the back, which requires a lot of lateral stretch from the chain. (© Pedal Street)

Using small-small or large-large cog/chainring combinations places a great deal of stress on the drivetrain. The chain stretches at a sharp angle, which inevitably causes an increased amount of wear and tear. In some situations, it can even cause the chain to slip off entirely.

Bicycle gear shifter types

There are several different types of gear shifters, some more cyclist-friendly than others. For the purposes of this guide, we’ll look at two main types of gear shifters—flat bar/mountain bike shifters (which encompass trigger, grip, and thumb shifters) and road bike shifters—and how to shift gears on each.

Trigger shifters

Trigger shifters on a mountain bike
Trigger shifters on the underside of a mountain bike’s handlebars. (© Pedal Street)

Trigger shifters are probably the most widely-used type of shifter on modern mountain bikes. The trigger shifter features two levers underneath the bike bars: one to shift up the gears, and the other to shift down. With a few exceptions, most trigger shifters will only allow you to switch one gear at a time.

Grip shifters

Grip shifters (also called twist shifters) are another shifting mechanism. The grip shift consists of a dial placed on the grip of the bars, which you’ll twist forward or backward in order to switch between gears. One downside to grip shifters is that they tend to require a rotating wrist movement that can occasionally cause repetitive stress injuries.

Thumb shifters

Thumb shifters have fallen out of common usage, though they can still be found on occasion. The thumb shifter lever is placed on the bars and can then be moved clockwise or counterclockwise depending on whether you would like to move to an easier gear or a more difficult one.

Road bike shifters

Road bike gear shifter
An example of a road bike gear shifter. A nudge of the black lever moves the chain in one direction. A nudge of the entire brake lever moves the chain in the opposite direction. (© Pedal Street)

Unlike flat bar or mountain bikes, the shifter and brakes on a road bike are normally a single unit. The shifter on the right-hand side will control rear shifting, while the one on the left-hand side controls front shifting. Depending on the type of bike, the shifter may contain one or two paddles or levers on each side, which are used to shift either the cassette or the chainring into easier or harder gears.

What if your chain comes off?

A chain coming off the gears of your bike should be treated similarly to a blown tire. If your bike drops its chain, slowly pull over to the side of the road as safely as possible. If the chain has dropped off the small chainring, you might be able to guide the chain back in place simply by using the left shifter to move the chain back onto the larger chainring while simultaneously pedaling forward slowly. Most of the time, however, you’ll need to manually shift the chain back onto the chainring.

First, push the rear derailleur forward to create slack on the chain. This will let you maneuver the chain carefully back onto the chainring. Once that’s done, lift the rear of your bike with one hand and then manually turn the pedals with your other hand in order to make sure the chain has caught. Often, this will be enough to get your bike back into working condition.

If you find that your bike is frequently dropping its chain, though, be sure to take it to a bike shop and have a professional take a look.

Frequently Asked Questions

Why do bikes have different numbers of gears?

Bikes have different numbers of gears because they are used for different things. Cruiser bikes intended for easy, mostly flat riding don’t need a lot of gears. Cyclocross bikes, which cover all sorts of terrain, need many. Bicycle manufacturers aim to give bikes an appropriate number of gears for their intended use.

Are more gears better?

It’s not necessarily better to have more gears, but it depends on why you’re cycling. Mountain bikes need many, so riders can travel across potentially steep terrain. However, casual or commuter cyclists don’t need many gears, which do add complexity and maintenance. Focus more on the gear range: As long as you have gears low enough for uphill climbs and high enough to generate downhill speed, you should have enough gears.

Do I need to know what number my gears are?

For most casual cyclists, the answer is no. You can identify the gear you’re in by multiplying the front gear number by the rear gear number (1 is the outermost gear at the front and the innermost gear at the back), but it’s much better to get a feel for which gear works best on whatever terrain you’re actually cycling, rather than by numbering gears. You’ll know it when you feel it.

What is a fixie bike?

A fixie bike is a type of single-speed bike that fixes the rear cog in place. In other words, if your bike is moving, the pedals are also moving. This means that you constantly need to pedal. On the upside, however, fixie bikes require less maintenance and are typically a lower cost option. They’re also great for fitness!

What is a hub gear?

Some bikes have an internal gear hub that takes the place of the cassettes, derailleurs, and multiple chainrings. There are several upsides to hub gears:

  • they require less maintenance than bikes without a hub gear
  • they’re much simpler to use
  • they allow you to switch easily between gears without pedaling

For these reasons, casual and commuter cyclists tend to find them more convenient to use. On the other hand, hub gears tend to be heavy and can weigh a bike down.