Bicycle Cassettes – Keeping the Derailleur Gears Ticking

The cassette on the bicycle consists of different sized cogs (or sprockets) – which is why it is also called a cogset or sprocket cluster. It sits on the freehub body on the rear wheel. The chain runs on the chainrings of the cassette and is moved between the gear cogs by the rear derailleur. Together with the front gear, this gives the bike its gear ratio. The gear ratio dictates how easily or hard you have to pedal on the bike to move forward. The principle behind it is simple: the smaller a cassette sprocket – i.e. the fewer teeth it has – the harder the gear. The more teeth a sprocket has, the easier the gear.

In order to offer plenty of gears and to make steps between gears as small as possible, developers have created gears with more and more sprockets over the years. A bike drivetrain currently has eleven to twelve gears or speeds. Depending on the brand, up to 13 gears are even possible. However, it is not just the number of sprockets that is key here, but above all their size or the number of teeth. The smallest sprockets have at least nine teeth, but usually eleven teeth. The largest sprockets in modern derailleurs for road bikes, trekking and touring bikes as well as e-bikes have 32 or 34 teeth. MTB cassettes, on the other hand, can even have sprockets with up to 52 teeth. There is a good reason for this: after all, mountain bikers often have to tackle very steep climbs on rough terrain. Particularly easy transitions are therefore a great advantage.

If you consider the number of teeth of the smallest and largest sprocket on a cassette together, that tells you the cassette’s capacity. A cassette with 11-32 teeth has a small capacity; the steps between the individual gears are rather small here. A cassette with 10-52 teeth, on the other hand, has a large capacity. But it also has very large steps between each gear.

The most important criterion when buying a cassette is the derailleur manufacturer. Common brands are Shimano, SRAM and Campagnolo. The respective manufacturer also determines the toothing between the cassette and the freehub onto which the cassette is placed. Shimano and SRAM use the same standard, which is also the most commonly used. However, SRAM uses its own standard called XD for current mountain bike groupsets with eleven and twelve gears. Campagnolo also uses its own standard.

In addition to the gear brand and the matching toothing on the freehub, you must of course choose a cassette that matches the number of gears on your bike. Modern derailleur gears have seven to 13 gears, i.e. with a corresponding number of sprockets on the cassette.

If you want to buy a new cassette to replace a worn one and you've been happy with the gear ratio on your bike up to now, simply buy the same cassette again: same manufacturer, same groupset, same capacity. That means the new cassette is guaranteed to fit and function without any problems. Incidentally, at BIKE24 you will find a large selection of different bicycle cassettes – from classic road bike cassettes to e-bike cassettes.

• The brands: SRAM and Shimano dominate the market for derailleur gears on bicycles, so the Shimano standard of toothing between the cassette and freehub is the most widespread. The traditional brand Campagnolo uses its own standard for its cassettes. There are also some smaller brands that offer their own groupsets or cassettes as replacement parts for the major brands' groupsets. Some of these companies rely on common standards, but in some cases they also have their own. As a rule of thumb, the cassette must fit the freehub on your rear wheel.
• How many gears: The number of sprockets is determined by your gear system’s gear shifter and rear derailleur. The cassette must always have exactly the number of sprockets for which the gear shifter mechanism is designed.
• The capacity: The smallest sprocket in a cassette is generally defined by the freehub. Eleven sprockets are the most common standard. However, you can vary the size of the largest sprocket and choose the largest possible sprocket for easy gears on mountain climbs or a smaller sprocket for smaller steps between gears. But be careful: the total capacity is still set by the rear derailleur. If you want to change something here, you'll need to check your rear derailleur’s operating instructions to see what the total capacity is.

As described above, the cassette has to fit the freehub. In addition, the number of sprockets must correspond to your groupset. If the gear shifter operates eleven gears, the cassette must have eleven sprockets as well. So long as these two conditions are met, you can also use cassettes from other cassette providers. Having said that, the components of modern derailleur gears are compatible with each other, so derailleur gears work best when all components are from the same brand. However, you can use cassettes from other groupsets within the brand without any problems.

You can also change the gear gradation of the new cassette for easier gears or fewer large steps between gears. But first you will need to make sure that the rear derailleur can handle this new capacity. You can find this out in the rear derailleur’s operating instructions. You may also need to fit a longer or shorter chain if you change the cassette’s capacity.

If you want to install cassettes yourself, you will need two special tools. Firstly, you need a cassette remover to open and close the end ring that secures the cassette to the freehub. You also need a counter holder, such as a chain whip, to prevent the cassette from rotating on the freehub when the end ring is opened. If you want to change cassettes yourself regularly, then investing in these two bicycle tools may be worthwhile.

To keep the cassette clean, you should always clean coarse dirt off immediately after a bike ride with a little water and a brush. Caution: Steam cleaners are generally taboo when cleaning bicycles, and this applies in particular to cassettes. The high pressure can cause water to enter the hub shell or destroy the lubrication of the bearings. When you clean your bike thoroughly, pull a cloth dipped in some oil thoroughly between all the cogs of the cassette. You don't need to oil or lubricate the cassette.