Buyers guide to road cassettes

Is your cassette worn out? Or maybe you feel the need for easier gears on hilly terrain? Here’s a comprehensive guide how to choose a replacement cassette.

A cassette is the collection of sprockets on the hub of the rear wheel.

The amount of sprockets determines the amount of gears available which you will often hear referred to as ‘speeds’ ie 8, 9, 10 or 11 speed. Cassettes must correspond with your current system and speeds. You cannot add or subtract from your current set up so you have to stick with your current number.

Each sprocket has a different amount of teeth. A higher amount of teeth makes it easier to pedal than a low number and vice versa. Most road bikes come supplied with a 12–25T cassette, where the smallest sprocket has 12 teeth and the largest sprocked has 25 teeth.

Go big to make life easier

If you’re struggling on the hills and want to make it easier then go for a cassette with lower gearing, ie greater number of teeth on the largest sprocket.

As most bikes come supplied with a cassette with a 25 tooth sprocket as the largest sprocket, if you switch to a cassette with a larger biggest sprocket (somewhere around 28 teeth) it will make a big difference. Bigger than you think. Three little teeth doesn’t sound like much difference but it really is.

The downsides of larger cassettes are a small weight penalty and a larger ‘jump’ between adjacent gears ie. sprockets next to each other are a bit more different in ratio compared to adjacent sprockets on a small cassette. Bigger cassettes can mess up your cadence and pedalling rhythm a bit basically. Some folk won’t mind (or even notice) but some riders might.


If you’re climbing really big hills and lots of them, then a 30+ tooth sprocket will help even more.

If you are going to a 30+ tooth sprocket you need to make sure your current rear derailleur can handle the bigger range. Generally speaking short cage rear derailleurs won’t work but medium and long cage derailleurs will.

In some cases you may have to put on a new longer chain as well if running a large sprocket cassette.

Bye-bye triple chainsets

A large cassette in conjunction with a double chainring compact chainset offers the same gear spread as a triple chainset system.

You don’t need a triple chainset. Well, unless you’re doing lots of miles, over mountains, whilst carrying loaded panniers. Moving to a triple chainset though means you have to potentially buy new gear shifters, front mech and a bottom bracket (depending on manufacturer).


Go small for speed

For racing and time trialling, a smaller rear sprocket such as an 11 tooth will really provide speed and should stop you spinning out if your current smallest sprocket has more teeth.

And, as mentioned above, smaller cassettes have less of a jump between adjacent sprockets. This makes it easier to maintain your cadence and rhythm, which is of real interest when racing.


When purchasing a cassette the first thing to take is to consideration is your current gearing system brand (Shimano, SRAM or Campagnolo) and the number of sprockets. The latter cannot change. You cannot mix and match different speed cassettes.

Campagnolo cassettes are only compatible with Campagnolo type hubs as the spacing and fitting mechanism is unique to them.

Shimano and SRAM are interchangeable as they have the same size hub fitting and attachment method; just make sure the number of sprockets is the same.

Who should buy what?

The best way to start your search is find out what you have at the moment and why you need to change it.

Regular riders – For most people a 12-25 will get you over most hills, especially when combined with a compact chainset.

Hill dwellers – If you live in a hilly area or simply want to make climbing easier, you should go for a 28+ tooth cassette.

Mountain riders – If you’re going to ride somewhere really mountainous such as the Alps, Pyrenees or Dolomites or doing something stupid in the UK like the Fred Whitton, go for a 30+ tooth cassette.

Speedy racers – If you find you are spinning out all the time, you need a bigger gear. An 11 tooth sprocket cassette will give you more top end speed – providing you have the legs to keep turning it!

Road bike cassettes at Merlin Cycles


Fitting a cassette

You need a couple of specific tools. A cassette lockring tool and a chain whip (pic above). You may need a big adjustable spanner too. Here’s a good video that shows you what to do.

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