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Your Guide to Rear Cassette

Learn how your rear cassette works. Because it’s important to know the basics

If you’re a beginner to road cycling you may be wondering about how some of the components on your bike work. Like the rear cassette.

The rear cassette is that bunch of gears that sits on the hub of your rear wheel and is driven by the chain.

Of course it’s obvious that as you turn the pedals the chain turns those gears, and the bike moves forward, but beyond that some beginners are a little confused about exactly how the rear cassette works, and what to buy if they’re buying one.

Basic bike gearing principles

The basic principle of bicycle gearing is that it allows you to pedal comfortably in different circumstances. In the past bikes were made with one gear only, and that was very awkward to use in any but the most ideal circumstances.

If you have only one gear on your bike then you may find it perfectly comfortable pedalling on the flat and a comfortable speed. But when you reach a hill you’ll find it gets harder and harder to pedal, you have to push more and the pedals turn slower, and if it gets steeper you may be unable to continue.

Go down the other side and you’ll probably be pedalling so fast that you’re not making much difference to your speed. You may as well roll. Bike gearing is designed to give you a range of gearing options so that you can pedal comfortably on any slope, up or down, at any speed.

Your gearing system consists of 2 sets of gears, (as well as various other components for shifting). The first of these two sets of gears is on your pedals. This consists of two (or sometimes three) rings, and your derailleur will shift your chain from one of these rings to the other, achieving a change of gear.

There are various technicalities to these front rings, which we shall consider another day. However the second set of gears on your bike is the rear cassette, or cluster, which we will talk about today.

The basics of rear cassettes for road bikes

There is a number of gears, or sprockets, on your rear cassette. These range from small through to large. With the development of gearing technology on bikes the number of sprockets has increased gradually over the years. When I started cycling eight was more common, then there was nine and now ten is relatively common though some new groupsets have eleven sprockets on the rear cassette.

The general rule is that where your chain is on the smallest sprocket your pedals will turn slower and you’ll need to push harder. Where your chain is on the largest sprocket your feet will spin faster and you won’t need to push as hard.

So the smallest sprocket is good for going downhills, where you’re moving faster, and the largest sprocket is good for going up hills, where you’re moving slowly and need to work hard.

Each sprocket is labelled with a number. The number refers to the number of teeth on the sprocket. So the number eleven, for example, has eleven teeth. The number twenty five has twenty five teeth. You get the idea.

But there’s many variations within that rule, specifically about which sprockets to choose for your cassette if you’re buying a bike, or a new cassette.

What to do if you’re buying a cassette or a new bike

So if you’re buying a bike, or replacing a cassette, you need to give some thought to exactly what gearing will suit you best. Sadly, to some degree this is too simple. For instance there are different cassette’s available for different brands. Shimano cassette’s are different to Campagnolo cassette’s which are different to Sram cassette’s. Some brands will allow sprocket sizes that others will not.

And there are also many options in the ranges of sprockets available. All of this is way too complex to canvass here, as this is intended as an introduction to the basics. However before choosing any cassette you will need to think about a few things. For instance:

  • If you’re replacing the current cassette are you having any gearing issues?
  • Do you run out of gears climbing steeper hills, and find that you’d like one or two more?
  • Do you commonly ride descents where you’d like to pedal harder but also run out of gears?
  • Do you prefer to push harder on the pedals but pedal slower or do you prefer to spin your feet faster?
  • Have you noticed any gaps between your gears (i.e. because you’re shifting too many teeth) that bother you?
  • What is the general terrain that you ride on? Are you generally riding on flatter terrain or do you more commonly ride more hilly country?
  • How fit are you? How old are you? How hard do you like to ride?

Answers to these questions will give you a better idea of what your requirements will be when looking for a cassette.

One good way to approach this is as I did. When replacing your existing cassette think about these questions before choosing a new one. Maybe talk to some friends about what cassette they use and what gear ranges they have, and how they find them?

And if you’re buying a bike for the first time talk to the shop about what cassette will go on the rear wheel, don’t just take whatever you’re given. Give them some information, such as answers to the questions above, to help them make a choice for you if you’re not comfortable with making a choice yourself.

Or preferably, as is always my preferred option, ride a selection of bikes and, if possible, different cassettes, on your normal terrain before choosing.

As you get more experienced you’ll learn more and more about choosing a rear cassette. Not only that but you’ll learn more about how to use it, how and when to replace it and more. You might even end up having several different cassettes so that you can put the ideal cassette on your bike for the type of terrain you’re riding that day.

But it always pays to think about your cassette carefully before making a choice. Because the choice you make will determine the comfort of your ride, every day you ride.

Last modified: January 5, 2021
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