21-Speed Bike Gears Explained (in a Way You’ll Understand)

21-speed bike explained

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Understanding the mechanics of a bicycle can sometimes seem a little daunting and finding clear cut information that is both easy to follow and understand can also be difficult at times.

But it really shouldn’t have to be. That’s why we have made this easy to understand run down of 21-speed bike gears and everything you need to know about them, from what makes a bike 21-speed, how to tell the difference and how to use one.

What is a 21-Speed Bike?

First and foremost, understanding what a 21-speed bike is will be the first step in this journey. Thankfully, this definition is straight forward and easy to comprehend.

A bike which has 21-speeds is one that has three chain rings (the round component that the chain runs along) at the front, with 7 gears at the back on the casette (spikey round component at the back which the chain runs along that consists of 7 different size cogs).

Therefore, because 3 x 7 + 21, you have 21 gears. Or alternatively, 21 speeds.

Bikes with 21-speeds are most commonly hybrids or off-road style bikes as they need the range of gearing for their intended usage to navigate up steep inclines and ensure comfort.

21 speed bike has 3 front chain rings and 7 rear cassette gears

21-Speed Bike Gears Explained

Now we’ve defined what makes a bicycle have 21-speeds and how to calculate if one does, it’s time to focus on their usage.

Although having 21-speeds may seem overwhelming, it really doesn’t have to be. See it this way: you have more options. This allows you to find the perfect gear to ensure your comfort while riding, regardless of where your bike takes you.

But how do you use this vast amount of gears? With ease: that’s how.

what gears to use explained

What Gears to Use on a 21-Speed Bike?

Knowing which gear to use when riding on a 21-speed bike doesn’t have to be a scary prospect, although we appreciate it may feel that way at first. But once you get the hang of it, it’ll become second nature.

When selecting the front chain ring at the front it’s important to consider the terrain you are riding along. If it’s flat, the biggest (outside) chainring will likely be best, whereas the middle chain ring will be most suited to gradual inclines and the smallest chainring for steep inclines.

The cogs at the back will determine how ‘easy’ it’ll feel to pedal. If you want to be able to ride faster then going down the cassette to a smaller cog is best whereas to spin more for hills etc, then going up the cassette to a larger cog will be favourable.

How to Ride a 21-Speed Bike

Now the gear selection is more clear, it’s time to explain how to ride a 21-speed bike.

Given most 21-speed bikes will either be, a mountain bike, touring bike or off-road hybrid, you’ll likely find yourself scaling some challenging terrain with your 21-speed bike.

Therefore it’s important to remember to change into the gear you want before you get to an obstacle to keep you momentum and to ensure you stay on top of the gear (can push the pedals with ease).

For example: if you are coming up to a steep climb on your mountain bike, drop into a smaller ring at the front and a higher cog at the back. This way you’ll be prepared and will be able to climb the hill without killing your speed.

Another example of when changing gear is vital is when coming up to junctions. If you are in the big ring and the smallest cog at the back, it’ll be much harder to get going from standstill. Therefore, drop into the middle chainring and the mid way point of the cassette. This will make starting again much easier.

18 vs 21 vs 27 bike gears
18-gear vs 21-gear vs 27-gear bikes

18-Gear vs 21-Gear vs 27-Gear Bikes

Now we’ve explained what a 21-speed bike is, what gears to use and how to ride one, comparing it to other options to understand how many gears you need is the last step.

With regards to 18-gear bikes, they can come in two forms. Either having a double chainring at the front, paired with a cassette consisting of 9 cogs. Or instead, three chainrings at the front with 6 cogs on the cassette at the back.

However, a 27-gear bike is one that has a triple chainring at the front, much like the 21-gear, but instead of only having 7 cogs on the cassette at the back, the 27-gear has 9.

But, an 18 gear bike with a double chainring at the front and 9 cogs at the back is lighter than the other three options and is better suited to road bikes or urban hybrids. But the 21-gear and 27-gear are great for ensuring range for bikes needing to get over varied terrain such as off-road.

Therefore, only you will know which is best suited to your needs. But be aware that some bikes won’t be available as standard with different gearing options. Although changes can be made to suit individual needs with regards to gearing.

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