What Is a 21-Speed Bike and How Does It Work?

A 21-speed bike has three front gears and seven in the rear.
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Most bicycles come equipped with gears to help riders tackle various terrains. Common gearing on bikes include 1, 3, 7, 18 and 21 speeds, and each speed refers to a different combination of gears. By changing the combination of these gears, you can make it more or less difficult to pedal.

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Once you learn the gearing of a 21-speed bike, you'll be able to enjoy longer rides that leave you less tired. So, let's get started — we've got everything you need to know about 21-speed bike gears explained!

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What Is a 21-Speed Bike?

A 21-speed bike can be any type of bike with 21 gears, whether that's a road bike, mountain bike, commuter bike or hybrid bike.

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A 21-speed bike generally offers a faster, smoother ride than bikes with fewer speeds, according to bike manufacturer Sixthreezero. But with that being said, its wide range of gears does allow you to ride at a slow pace, go all out or anything in between.

To get a bit more technical, a 21-speed bike has three front gears and seven in the rear. The front gears sit in line with the pedals and are called chainrings. The rear gears are in line with the axle of the rear wheel and are called the cassette collectively and cogs (gears) individually.

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The large and small chainrings are intended for extreme circumstances: large hills or fast road riding. Shift your bike into a super low gear to make your uphills easier and shift it into a high gear to make your downhills faster, according to bike manufacturer Liv Cycling. (We'll get into this a bit more below.)

Don't use the small chainring with the smallest cogs in the cassette or the large chainring with the largest cogs. (Colloquially, this is called "cross-chaining.") This places the chain at too much of an angle, increasing wear on your bike and raising the risk of your chain jumping off the gears while riding.

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The 5 Main Components of a 21-Speed Bike

Before going any further, it's helpful to understand all the parts of a 21-speed bike. Here are the five main components, according to outdoor retailer REI:

  1. Cassette:‌ A group of gears (cogs) located at the rear wheel of your bike.
  2. Chain:‌ A metal link that connects the front chainrings to the cassette so that when you turn your pedals, your wheels also turn.
  3. Crankset:‌ The part of your bike the pedals are attached to. It transfers power from the rider to the rear wheel. A 21-speed bike usually has three chainrings on the crankset.
  4. Derailleur:‌ A mechanism controlled by your shifters (below) that moves your bike chain from one gear to another. Most bikes have derailleur in the rear, but not all have one in the front.
  5. Shifters:‌ Controls located at your bike's handlebars — which operate the derailleur via cables — that allow you to shift gears.

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How to Use a 21-Speed Bike

It's difficult to enjoy biking when your feet can barely move the pedals or when the pedals spin so fast your feet cannot keep up. Adjusting the gearing of your bike allows you to keep your preferred pedaling cadence when traveling at any speed.

A derailleur is used to switch between gears. The derailleur is controlled by shifters mounted on the handlebars. Typically, your left shifter controls your front brake and front derailleur (front chainrings) and your right shifter controls your rear brake and rear derailleur (rear chainrings). The shifter changes the position of the derailleur, causing the chain to derail from the current gear and jump to the next larger or smaller gear. You need to continue pedaling when you shift gears.

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Low gears (gears one through seven) are best for climbing hills. Your lowest gear on your bike is the smallest chain ring in the front and the largest cog on your cassette, according to Liv Cycling. Downshift into this position when you want your pedaling to be easiest with the least amount of resistance.

High gears (gears 14 through 21) are best for going down hills. Your highest gear on your bike is the largest chain ring in the front and the smallest cog on your cassette. Upshift into this position when you want your pedaling to be the hardest with the most amount of resistance — ideal for accelerating down hills.

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How to Choose the Right Gear on Your 21-Speed Bike

Because a 21-speed bike has such a wide variety of gears, you'll have to experiment with which specific gears are best for you on different types of terrain — after all, everyone is different and no one has the same preferences.

Choose a gear you find comfortable. Begin with the middle chainring and a medium cog in the cassette, number four on a 21-speed bike. Make small adjustments with your left shifter to adjust the cassette while you continue pedaling.

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To speed up your cadence, choose a smaller cog such as numbers five, six or seven on a 21-speed bike. To slow down your cadence, choose a larger gear such as numbers one, two or three. If the number one or number seven cog is not fast or slow enough for you, move your cassette back to number four and adjust the chainring. Again, continue to pedal as you shift gears.

A 21-Speed Bike vs. an 18-Speed Bike

An 18-speed bike has, you guessed it, 18 gears (as opposed to 21). They have a wide range of gears to shift through, which helps you ride through a number of different types of terrain with ease — albeit not as wide of a range as a 21-speed bike.

Both an 18- and 21-speed bike have three chainrings in the front, but the 18-speed has six cogs in the rear while the 21-speed has seven, according to Popular Cyclist. However, an 18-speed bike can also have two chainrings in the front and nine cogs in the rear. The latter option tends to offer a bit more speed and power than the former.

Parts on a 21-speed versus an 18-speed bike may be interchangeable, but not always, so check with your bike's owner's manual or your local bike shop before making any changes.

Tips for Easier Gear Shifting

To make your gears work for you, shift into an easier gear as you approach a climb or begin to fatigue. If your cadence starts to drop for any reason, take this a signal to switch to an easier gear. On the other hand, capitalize on flats, descents and tailwinds by shifting into harder gears. This will allow you to increase your speed while maintaining the same cadence and exertion level.

Here are a few more tips for making the most out of your gear shifting.

1. Anticipate Shifting Gears Ahead of Time

Start thinking about shifting gears before you reach an obstacle, such as a hill. If you wait until you're halfway up a hill and can barely pedal, shifting gears is difficult. Pedal softly for a few rotations as you shift gears. Too much pressure can prevent gears from shifting, or it can make your derailleur skip gears, resulting in grinding between the chain and derailleur.

2. Don't Forget to Shift Into an Easier Gear When Approaching a Stop

If you're cruising on a flat or have a tailwind pushing you along, you may be riding in one of your hardest gears. That's great, until you come to a stop and attempt to get going again in that same gear. Make regaining momentum much easier by shifting down a few gears as you approach stops.

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