What is a bike cassette?

A bike cassette is an integral part of your bike’s drivetrain. Found on the drive side of your rear hub, it consists of a number of circular metal discs with teeth around the edge, ranging from small to large – these are called ‘sprockets’. If you are thinking of buying a new cassette, read on for more information.

When shopping for a new road bike cassette or one for your mountain bike, you will notice that they vary in specification, from number of sprockets to number of teeth on each sprocket.

A bike cassette will typically have 8, 9, 10, 11, 12 or even 13 sprockets depending on the amount of gears in your transmission and type of bike. For example, a drivetrain with a 9-sprocket cassette and three front chainrings offers 27 gears in total (3×9), while two chainrings up front and a 10-speed cassette will deliver 20 gear options (2×10).

Sprockets vary in size according to the number of teeth they have. The cassette on a bicycle may, for example, be sized as 11-32t. The first number refers to the number of teeth on the smallest sprocket (the highest gear, for fast pedalling at speed) and the second number to the biggest sprocket (the lowest gear, for climbing hills). The closer the two figures are together, the less pronounced the difference between gears (e.g. an 11-21t cassette is referred to as having a ‘narrow’ gear range, and an 11-34t as having a ‘wide’ gear range).

Gear Ratios

The range of gears on your cassette, combined with the size and number of your front chainrings, gives you your bike’s gear ratio or ‘gearing’. Bikes that will tackle a wide variety of terrain – on- and off-road – require a wide range of gears, while professional race/time trial bikes more often require a narrower range and smoother jumps between gears.

Your bike cassette, along with other parts of your drivetrain, will wear with time so it’s important to keep it clean and well-lubricated, and to replace when it’s worn out.

Cassette Brands

In some circumstances, you may be able to use a bike cassette from a different manufacturer than that of the rest of your drivetrain. Shimano and SRAM cassettes are generally interchangeable on both road and mountain bikes since the sprocket spacing is the same – however some modern groupsets may require a specific cassette to fit – look out for specific instructions on types of ‘driver bodies’ a cassette will fit. Campagnolo road cassettes, on the other hand, will only operate with Campagnolo drivetrains.

While the bulk of our bike cassettes are for road and mountain bikes, we do also stock options for gravel, hybrid and commuter bikes.

Road Cassettes

Road cassettes typically feature 9, 10, 11 or 12 sprockets with narrower jumps in gears offering smoother shifts to help achieve optimum cadence (number of pedal revolutions per minute).

Most road cassettes will feature a 12-tooth sprocket as the highest gear with a low gear of between 25 and 32 teeth. A 12-25t road sprocket is regarded as standard, but lower gearing (e.g. 12-32t) is increasingly being specced on bikes aimed at beginners, endurance/sportive riders or just anyone who wants an easier time in hilly terrain. If you do want a lower gear when replacing a worn, old cassette, check that your rear derailleur is compatible as larger sprockets may require a long-cage model.

Time for a New Road Bike Cassette?

When replacing your road cassette – rough shifts or frequent chain slippage will tell you that it’s time for a new one – remember that you must get one with the same number of sprockets as your old one. You cannot replace a 9-speed cassette with a 10-speed as the greater number of gears requires a different width chain.

Upgrading to a new cassette such as a lighter model may save you grams, but it will come at a price as top-end cassettes are expensive. However, for those seeking peak performance a lot can be gained from modern components compared to an old cassette. Complete road bike groupsets are also available to buy.

Mountain Bike Cassettes

MTB cassettes will typically offer a wide range of gears in order to enable riders cope with the varying terrain that they may face – from short, steep technical climbs that require very low gearing (biggest sprocket) to longer descents that can be pedalled fast (smallest sprocket). They typically differ from road bike cassettes in having greater gaps in gearing between each sprocket.

Most MTB bikes use 9- 10- 11- or 12 speed cassettes although more budget models may use 8- or less commonly, 7-speed. A typical gear spread for an MTB cassette (the amount of teeth on the smallest and largest sprockets) would be 11-34t.

Cassette Spares

On modern MTB and road bikes, a whole cassette is sold as a replacement rather than as individual sprockets. However the special lockring that secures the cassette to your freehub body may require replacement in the event of damage.

If you need to remove your cassette in order to fit a new one or replace the lockring you will need specialised tools including a chain whip tool and cassette removal tool, as a well as a good adjustable spanner.

How to Remove a Cassette From a Bike

Here are a few simple steps to follow if you want to change a bike cassette:

Changing your bike cassette first requires removal of the rear wheel from the frame – once done follow the steps below.

How to change a bike cassette:

• Once you have the wheel out of your bike, using the correct lockring removal tool (SRAM/Shimano are the same – Campagnolo is a subtly different spline type) and a chain whip, you can begin cassette removal.
• Place the lockring removal tool into the splined lockring that sits below the smallest sprocket. Make sure it’s firmly enmeshed with the splines.
• The lockring itself unscrews the same way as the freewheel so this is where you need a chainwhip to prevent the cassette from spinning when applying force to the tool.
• Wrap the chain whip around the cassette so that you can prevent the cassette/freehub from spinning freely.
• Once the chainwhip and lockring tool are secure, apply force to the lockring tool while holding the chainwhip to prevent spinning. This will release the lockring.
• Unscrew and remove the lockring. With the lockring off you can now remove the cassette.
• Attaching the new cassette will not require the chainwhip, just the lockring tool to tighten the lockring. Just be sure to correctly line up the splines on the new cassette with the splines on the wheel’s freehub body.

Cassette Tool Line-Up

At Sigma Sports, we have tools ranging from a cassette lockring tool or torque wrench, to a strong chain whip lineup, so you can top up your toolbox for any home repairs. If you do want to replace the cassette on your bike and want some expert input, our workshop team are also available to help. A bike mechanic can replace your cassette and make sure everything is properly aligned so you can cycle with confidence.

Beyond this if you want to partner your new cassette with other components such as a rear derailleur, rear wheel or chain, you will find a wide selection in stock. Remember to keep your new cassette – and the rest of your drivetrain – clean and well-lubricated to extend its life.