How to Choose the Right Bike Cassette

Choosing the right cassette for your bike doesn't need to be complicated.

Whether you're replacing a worn cassette or changing your gearing for easier climbing, this guide explains the key things to check before buying.

Your cassette affects the range of gears available on your bike, but not every cassette will fit every drivetrain. The number of speeds, sprocket sizes, freehub body and derailleur compatibility all matter.

1. Check how many speeds your bike has

The first thing to establish is how many sprockets are on your existing rear cassette.

Count the individual sprockets on the rear wheel. You might have 8, 9, 10, 11, 12 or even 13, depending on your drivetrain.

When replacing a cassette, the safest starting point is to match the number of speeds fitted to your current drivetrain.

PBP Tip: A 12-speed cassette isn't automatically compatible with every 12-speed groupset. Chain, shifting system and freehub requirements can differ between manufacturers.

2. Understand cassette ratios

Cassette sizes are usually written as two numbers, such as 11–28T, 11–32T or 11–34T.

These numbers refer to the smallest and largest sprockets:

• 11T means the smallest sprocket has 11 teeth.
• 34T means the largest sprocket has 34 teeth.
• The letter T simply stands for teeth.

The smaller sprocket is used for higher gearing, while the larger sprocket gives you an easier gear for climbing.

For the same front chainring, a cassette with a larger biggest sprocket will provide an easier lowest gear.

PBP Tip: A wider-range cassette doesn't automatically make your bike faster. Its main benefit is giving you a broader selection of gearing, often including an easier climbing gear.

3. Choose the right gearing for your riding

The ideal cassette depends on where and how you ride.

Road cycling

A relatively close-ratio cassette can provide smaller steps between gears, helping you maintain a comfortable pedalling cadence.

If you regularly tackle steep climbs, you may prefer a cassette with a larger biggest sprocket, provided your drivetrain supports it.

Mountain biking

MTB riders often benefit from wide-range cassettes, particularly when using a single front chainring.

The easier climbing gears can be useful on steep off-road terrain, while smaller sprockets provide higher gears for faster sections.

Gravel riding

Gravel bikes can require a balance between efficient road gearing and easier climbing gears for rough surfaces, loose terrain and longer adventures.

The right cassette depends on whether you're using a single or double front chainring and on your drivetrain's compatibility.

PBP Tip: Don't choose a cassette based on Road, MTB or Gravel labels alone. Some components can be used across disciplines, but the complete drivetrain still needs to be compatible.

4. Check your freehub compatibility

Your cassette fits onto the freehub body at the centre of your rear wheel.

Different cassette systems use different mounting standards, so identifying your freehub is essential.

Common examples include:

• Shimano HG-type splined freehubs: Used by many cassette systems, but compatibility varies by cassette model and freehub dimensions.
• Shimano Micro Spline: Used by many Shimano 12-speed MTB cassettes.
• SRAM XD: Used by various SRAM MTB cassettes and some other compatible systems.
• SRAM XDR: Used by various SRAM road and gravel cassette systems.
• Campagnolo and other proprietary systems: May require a different freehub interface.

Some combinations require specific spacers.

PBP Tip: Matching the number of speeds is not enough to guarantee a cassette will fit your wheel. Always check the exact cassette model against your freehub specification.

5. Check your rear derailleur capacity

Before changing to a cassette with a larger biggest sprocket, confirm that your rear derailleur supports it.

Two important specifications are:

• Maximum sprocket size: The largest rear sprocket your derailleur is designed to accommodate.
• Total drivetrain capacity: How much chain slack the derailleur can manage across your chainring and cassette combinations.

For example, changing from an 11–28T cassette to an 11–34T cassette could provide easier climbing gears, but only if the derailleur and the rest of the drivetrain support the change.

You may also need to check chain length and the manufacturer's installation requirements.

PBP Tip: Don't assume that a longer derailleur cage automatically makes any wide-range cassette compatible. Always check the manufacturer's specifications.

6. Do Shimano, SRAM and Campagnolo cassettes interchange?

Sometimes, but not always.

Compatibility depends on the particular models and drivetrain systems, rather than the brand names alone.

Things to check include:

• Number of speeds.
• Required chain type.
• Sprocket spacing and shifting compatibility.
• Freehub mounting standard.
• Rear derailleur requirements.

Some combinations are compatible across brands, but others require specific components.

PBP Tip: When in doubt, checking the manufacturer's compatibility information is safer than relying on speed and brand alone.

7. Should you replace your chain at the same time?

It's worth checking your chain whenever you replace a cassette.

A worn chain can accelerate drivetrain wear, and fitting a worn chain to a new cassette may affect performance.

Use a suitable chain wear checker and follow the chain manufacturer's recommended wear limits.

A new cassette doesn't always require a new chain, but both components should be in suitable condition and compatible with each other.

For more information, read our guide to checking your bike cassette for wear.

8. Your cassette buying checklist

Before ordering, make sure you know:

• The number of speeds on your drivetrain.
• Your current cassette model, if identifiable.
• Your preferred sprocket range.
• Your wheel's freehub standard.
• Your rear derailleur's supported sprocket size and capacity.
• Any chain or manufacturer-specific compatibility requirements.

If you're replacing your existing cassette and you're happy with your current gearing, choosing the same compatible model and ratio is often the simplest option.

Find the Right Cassette at Pro Bike Parts

At Pro Bike Parts, we stock a range of cassettes for road, mountain and gravel bikes, alongside chains, maintenance tools and lubricants.

Use our cassette collection filters to narrow down your options by speed, ratio, brand and freehub compatibility.

Still unsure which cassette you need? Check the model numbers on your existing components and contact us with your drivetrain and wheel details before ordering.