Bike Gears Explained – Everything You Need to Know About Shifting

Here we have bike gears explained in simple words.

As an engineer, I like to understand how things work in the most basic way. I’ve been riding since I was a kid, and I learned a lot about gears when I designed my own bike. In this article, I explain how bike gears work so you can finally understand your bike gears and get the most out of them.

We will explore the different types of bike gears, how they work, and how to use them:

Keep reading if you want to know more about this essential piece of your bike.

What are bike gears?

Bike gears refer to the different combinations of chainrings (attached to the pedals) and cassette cogs (attached to the rear wheel) on a bicycle. Their combination allows you to adjust the effort required to pedal and the speed.

When you pedal, you apply force to the cranks and move them in a rotary motion. But is the wheel that makes your bike move, not the pedals themselves. With the help of a chain or belt, gears connect the moving pedals to the rear wheel, so when the pedals move the wheel moves too. This is the gears’ main function, so you can sit comfortably without stretching your legs to reach the wheels. Imagine how uncomfortable bikes would be if you had to pedal directly into the wheels!

This is how bikes would look without gears

But gears are much more than a convenient mechanism. Gears are one of the most important inventions in the world. In simple words, they let you trade force for speed and vice versa. That is a huge deal.

If you are climbing up a steep hill, you can downshift and make it way easier. You then start pedaling faster, but the required force reduces. Same way, think about what happens when you are aiming for high speeds. On a flat trail, you shift up your gears, put yourself up, and start pedaling hard. Suddenly, you are flying fast.

The overall effort keeps almost the same. What changes is the way it is delivered.

Why are gears needed?

Gears allow you to adapt your effort to every terrain and speed. There’s only so much force you can produce and a top speed for your legs. The average person runs at 7mph (11km/h), so imagine how fast you should move your legs to reach 15mph (24km/h). With gears, it is easy. They allow you to trade force for speed and then reach higher velocities.

How many gears do I need?

Having lots of gears won’t make your bike faster. Instead, it will offer a wide range of options for efficiency. For example, a bike with two gears could go either fast or hard. But a bike with six gears will have four extra options between, so there is not a big leap from one to another. That way, you will find a more suitable cycling speed and effort in every situation.

Types of bike gears

External drivetrain

Bike Gears Explained
Components of external drivetrain gears

Odds are that your bike has this type of gear. It is the most common one due to its simplicity and effectiveness.

Bike gears have five main components:

  • Chainrings: Set of sprockets connected to the cranks and pedals.
  • Cassette: Set of cogs connected to the rear wheel.
  • Chain: The metal piece that connects the chainrings with the cassette.
  • Derailleurs: Little components that move and guide the chain from one sprocket to another.
  • Shifters: Located in the handlebars. When pressed, the derailleurs move by cables or servomotors.

Hub gear

Urban bikes often use hub gears due to their low maintenance

In contrast with external drivetrains, hub gears offer a packed solution. A shell protects gears from the outside, making them low maintenance. Even so, it comes with a price. All the metal pieces are now contained in a single cage, so weight spikes up. Also, its tightness will make repairs drain your patience or your wallet if it ever breaks down.

The range between high and low gears is quite small, so they are not as versatile as external drives. Hub gears allow you to shift gears without moving, which makes them ideal for commuters. Also, its low maintenance is a plus.

Gearbox

The main difference between hub gears and gearboxes is placement. Having the weight concentrated in the rear wheel is a deal breaker because of control and suspension. Especially for mountain bikes.

While hub gears locate in the rear wheel, gearboxes sit within the frame near the chainrings. This centralizes the heavy weight of the gears.

Whereas suspension and maintenance improve, price and heaviness still are the main drawbacks.

Fixed gears

Fixed gears are the most simple ones

With a fixed gear you get to simplify your bike. One chainring and a single cog, that’s it. This of course makes it the cheapest option and the least versatile.

The adaptability to different terrains and steepness that gears provide are gone. Single-speed bikes are hard to see nowadays for a reason. And they can get as rudimentary as having the chainring fixed to the pedals, so you can not stop pedaling while the bike is moving.

Still, the main benefit of fixed gears is simplicity. The least components, the cheapest, and most fail-proof.

Electric bikes

Electric bikes get one type of gear and add a motor

Electric bikes might seem more complicated at first. But they are not. They just get one type of gear and add a motor.

This motor can be in the bike frame or in one of the wheels, changing the weight distribution. It also influences how it applies power. A motor located in the chainrings will need a different speed than one placed in the wheel.

There are two ways a motor can power an electric bike:

Throttle assist

It replaces pedaling. When you hit the throttle, the motor spins whether you are applying force or not, like a motorbike. It requires more power, so the battery drains fast.

Pedal assist

It doesn’t move by itself. Instead, it acts as a support so you don’t have to put all the effort by yourself.

A sensor measures the amount of force you apply in the cranks. Depending on that force, the motor spins at the same time as your legs.

How do bike gears work?

Bike gears work by changing the number of times the rear wheel turns by each time the pedals turn. This allows you to move at a comfortable speed for the terrain and your fitness level.

Let’s put an example.

Imagine that your chainring has 25 teeth, and your current rear cog also has 25 teeth. That is a 1:1 ratio, which means that the wheel will turn 1 time for every single turn of the cranks. This ratio also applies to strength. The same force you apply to the pedals will apply to the wheel.

This is also true for every gear, so let’s see how the number of teeth affects your riding:

Downshift

Downshifting puts the chain to a bigger rear sprocket

When you downshift, the derailleur moves the chain to a bigger rear cog. For example, imagine a cassette sprocket with 50 teeth and a chainring with 25. In this case, the ratio is 25/50 = 0.5, which means that the wheel will make half a turn for every pedal stroke. But, the force you apply in the pedals will double in the wheel.

Upshift

Upshifting puts the chain to a smaller rear cog

When you upshift, the derailleur moves the chain to a smaller cog. For example, imagine a cassette sprocket with 25 teeth and a chainring with 50. In this case, the ratio is 50/25 = 2, which means that the wheel will turn twice for every pedal stroke. But, you will need to put more strength into the pedals, as the force in the wheel halves.

How to use bike gears

Know your shifters

First of all, you need to know how to even shift a gear. Almost every bike will shift chainrings with your left hand, and the rear cogs with the right one. To do that, it will have one of the following shifters in the handlebar:

Trigger

Trigger shifters have levers or buttons

Trigger shifters are the most common ones. Each bar has two levers or buttons, one for the thumb and the other for the index finger. Pressing them will move your derailleurs and change gears. Some even allow you to shift many gears at once.

These are newer versions of thumb shifters, which worked by pressure. You moved a lever with your thumb, and the derailleurs moved too. But there were no defined positions. You moved the lever up and down until the chain changed its position.

Road bikes work a little bit differently, but they also use trigger shifters.

Road bike shifters have levers near the brakes

There are three main road bike gears manufacturers:

  • SRAM Double Tap: If you push the lever it will move the derailleur to a smaller cog or chainring. If you keep pushing past it then it will move to a bigger one.
  • Shimano Total Integration: The whole brake lever acts as a lever to shift into a larger sprocket or chainring. There is also a smaller lever next to it for shifting to lower gears.
  • Campagnolo Ergopower: They also have an index finger lever that will move to bigger cogs or chainrings. But, in this case, there is a thumb lever to lower gears.

For more information about how road shifters work, check out this video.

Grip

Grip shifters integrate into the handlebar’s grips. They have no levers

Grip shifters merge with the handlebar. Instead of pushing levers, you twist your grippers up or down to shift gears. This makes for the fastest way to change velocities.

As a counterpart, you have less sensitivity over the shifts. Trigger shifters let you better feel the gears and intuitively know what is going on.

What gear should I be in?

There is no right or wrong gear to be in, just choose what better works for you in every moment.

You have probably heard about how cars have power. It is a measure of how much force they can produce at a given speed. Think about two cars, one with 100HP and the other with 200HP. Both will be able to reach 80mph (130km/h) on a flat road, but only the 200HP one will maintain it in a steep uphill.

The higher the speed, the lower the force. And vice versa.

Your legs work the same way. They have a set power they can deliver in the form of force or speed. It’s up to you how you distribute that power. More force and less speed, less force and more speed, same force as speed…

We all have a preferred split. Some prefer to pedal faster, and some prefer to pedal harder. Gears will redistribute the power so the bike outputs more speed or force without having to change your pedaling.

But that would be in an ideal world. In reality, the gear you should be in is the one that allows you to comfortably achieve your desired speed and force. You will adapt not only gears but also yourself. On a steep hill, you will downshift and pedal faster. To reach high speeds you will upshift and pedal harder. It’s the combination of gears plus your own effort which will determine how the bike moves.

You have a desired pace for a given terrain, and a given effort you are willing to put in. Gears are the link between the two.

When should I shift my gears?

You have to shift gears when you feel too much or too little resistance. Also, you must shift making sure that the chain keeps always aligned.

Most bikes with external drivetrains have three chainrings in the front. In the rear wheel this quantity varies from bike to bike, but let’s say you have six. If that is the case, you could consider the following pairings:

Smaller chainring with the bigger two rear cogs: You will pedal fast but move slowly. This will make climbing hills easy.

Middle chainrings with the middle two rear cogs: This is the middle point. Ideal for starting pedaling, commuting, and difficult trails.

Bigger chainrings with the smaller two cogs: You will pedal hard and move fast. This will make for the fastest speeds, but impossible to climb hills.

As a rule of thumb, you should start with the middle-low gears. For example, the middle chainring and the third smaller rear cog. This will require you to do an acceptable amount of force to start moving. Not too much so you can’t even pedal, not too little so you spin like a windmill. Just enough.

Our goal will be to keep a similar amount of force at every time. So if you feel too much resistance, you should downshift. And if your legs are moving like crazy, you should upshift. Bringing the chain closer to the bike makes pedaling easier, and moving it away increases your speed.

The shifters of your right hand are for small adjustments, as they change your rear cogs. You should always use these first. Your left-hand shifters produce bigger changes, as it changes the chainrings. You must use them when aiming for speed or upclimbing.

Also, keep in mind that you can’t shift gears without moving. So always remember to return to the starting gears before completely stopping the bike.

Basic bike gears cleaning and maintenance

Make sure to do your maintenance on the chain and sprockets

The main component to look after is the chain. The wear of the chain is a clear representation of the health of the gears. It is important to keep it clean and tight, as it will affect your riding efficiency.

You can do most of the maintenance by yourself with a little help, but we highly encourage you to visit a specialist.

Tightening

Always check your derailleurs’ tightness, because they keep the chain in place

Tightening is the most important thing to check in your bike gears. Always make sure your chain or belt is tight. If it is not, check your derailleurs. They have little pulley wheels that guide and tighten your chain. There is a sweet middle point in which your chain will shift gears and not force the sprockets with too much pressure.

This is especially important for mountain bikes, as bumps will move and change the chain’s position. If it is too slack, it could get off the sprockets.

Cables are also important for gears. They move the derailleurs, so make sure they have an appropriate tightness. You will know it by feeling the shifters. If you find it too soft or too hard when changing gears, it may be worth checking the cables. Keep in mind that some high-tech bikes don’t have cables, they use servo motors.

Cleaning

Keep your gears clean to prevent wear

You should clean your drivetrain after every ride, especially if riding in nature. Dirt will accumulate and hinder meshing. It can even produce wear on the sprockets over time, which are far more difficult and expensive to change than the chain. Every once in a while, you should disassemble it, check for rust and fray in the cables and give it a deep wash.

Lubrication

Always keep your chain lubed. It helps it bend smoothly and mesh with the cogs.

A lubed chain vs a rusty one it’s like night and day. Gears shift without effort, wear and rust reduce, and your pedaling feels awesome.

While tightening is crucial for safety concerns, lubrication is essential for long-term maintenance

Common bike gears problems

Cross-chaining

Cross-chaining misaligns the chain and messes its tightening

Cross-chaining is the act of riding with your chain crossed. That means, with both your bigger rear cog and chainring at the same time, or with the smaller ones.

Cross-chaining forces your chain and gears. This harms your bike and your riding, increasing wear and reducing your performance.

Your gears will perform best when the chain aligns in a straight line from the chainrings to the cassette.

Dropped chain

Chain drops are very common, and indicate a problem in the gears

If your chain comes off while riding you should check your gears. You most likely have one of two scenarios:

  • Chain drops while shifting: Something in your gears has moved and there is probably a misalignment. Make sure that every bolt is tight. Cassette, Chainrings, and derailleurs must be in place, and your rear wheel completely aligned with the rest of the bike. Check if there are any hits, as they could have moved some pieces. Also, make sure your shifter’s cables are tight and your gears lubed.
  • Chain drops in bumps: It is probably a tightness issue. Most bikes have stabilizer systems in the rear derailleur, so make sure it is working. It must keep a constant tension and be able to reduce chain bounce.

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Picture of Daniel Espada

Daniel Espada

Daniel Espada is a passionate adventurer, certified scuba diver, and the mind behind geardventure.com. With a background in Engineering, Daniel combines his technical knowledge and love for the outdoors to create content that not only informs, but inspires action.
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