The vast majority of modern bicycles, whether mountain, road, or go-kart, come with derailleurs. The rear derailleur moves your chain up or down to a set of sprockets mounted on the hub of the rear wheel. These sprockets (or gears, or sprockets, whatever you want to call them) are your cassette.
Cassettes come in a variety of sizes to suit different uses. The size of a cassette is usually indicated by citing its minimum and maximum cog tooth count. For example, a typical modern road bike cassette might be an 11-32t (tooth) cassette. For a mountain bike cassette, the range might be 10-52t.
In this article, we'll teach you what a cassette is and how to tell the "speed" of a cassette, explain the typical gear ranges of cassettes for all disciplines of riding, compare the main differences between cheap and high-priced cassettes, and more.
What is a cassette?
▲ The cassette is an important part of most bicycle drivetrains
While it may seem simple, a bicycle cassette requires a lot of engineering.
The multiple sprockets in a cassette are not just a set of gears, but are designed to work together as a whole, with the individual sprockets precisely positioned relative to each other to ensure that the chain shifts smoothly between gears.
The individual teeth on the sprockets are shaped differently, and there are often ramps on the sides of the sprockets. This helps ensure a smooth transition of the chain between gears.
The design of these gear change avoidance ramps has been honed over the years.
For example, Shimano uses a system called Hyperglide, which is designed to provide a smooth shifting experience. The latest cassettes have updated this system, called Hyperglide+, which Shimano says can reduce shift times by one-third compared to Hyperglide and improve the performance of up and down gear shifting under high loads.
Other cassette suppliers, such as SRAM and Campagnolo, also have cassette designs that are equally effective.
▲Flywheels usually need to be replaced as a whole
Since they are designed as an integral system, the sprockets in the flywheel are sold as a set, not individually, and usually need to be replaced as a whole.
And in most cases, you can't just replace one sprocket in a set of flywheels with a sprocket with a different number of teeth, otherwise it will affect the shifting performance.
What is the "speed" of my flywheel?
▲Campagnolo Ekar gravel road groupset comes with a 13-speed cassette and a 9-tooth sprocket
Flywheels can have anywhere from 7 to 13 sprockets.
Nowadays, it is increasingly common to see high-spec road bikes equipped with 12-speed transmissions. After SRAM and Campagnolo have both entered the 12-speed era, Shimano has finally joined the road bike 12-speed club in 2021 with the launch of the Dura-Ace Di2 R9200 groupset.
For mountain bikes, 12-speed cassettes are largely the default configuration for mid-to-high kits, paired with a single crankset.
The number of sprockets on a cassette must match the speeds that the other components are designed for.
This is because almost all shifting systems are actively guided, and the derailleurs are designed to move a fixed distance with each click of their mechanism. This means that they will not work with cassettes that do not have the same number of sprockets, because the chain spacing of cassettes with more sprockets is narrower. The width of the chain must also match the number of sprockets.
▲SRAM's XO1 DH groupset is a typical counterexample to the current mainstream "more is better" thinking mode
Generally speaking, low-level groupsets offer fewer gear ratios, so the cassettes also have fewer sprockets.
However, there are exceptions. SRAM's X01 DH and GX DH mountain downhill groupsets use a seven-speed cassette that can be used with an 11-speed chain. Fewer speeds are to provide closer transmission ratios for each gear and allow for the use of shorter rear derailleur guides for greater ground clearance, suitable for bikes that do not need climbing ability.
Gear Ratios
▲SRAM Eagle offers an oversized 52-tooth sprocket on some cassette models
In addition to the number of sprockets, the different tooth ranges offered are also a key determinant of the compatibility of a cassette with your drivetrain.
Generally speaking, cassettes start at 10, 11 or 12 teeth. There are exceptions, such as some offering options for the smallest sprocket at 9, 13 or 14 teeth.
You may sometimes see brands present their cassettes in the form of a percentage of gear range.
For example, SRAM's 10-52t cassette has a gear range of 520%. How did SRAM come up with this number? How do you calculate your gear range percentage?
In simple terms, the smallest sprocket is 10 teeth, and the largest sprocket is 52 teeth, which is 520% of a 10-tooth gear, so the gear range is 520%.
It is important to note that this number only represents the range of gears on the cassette, and does not mean that you can increase your riding distance by the same proportion through such a gear ratio range.
Likewise, it doesn't tell you if it's the right cassette for your type of riding. For that, you need to calculate the actual gear ratio, which is another topic in itself.
▲ 11-28 cassette was once considered a large-ratio training cassette, but now it's at the smaller end of the standard range for road bikes
In recent years, the size of road cassettes has increased rapidly.
A few years ago, 11-28 was considered a "lightweight" training cassette, but now the smallest cassette available for Shimano Dura-Ace R9200 is 11-28. This may not sound like much, but considering that professional riders in the past usually used 11-23 or 11-25 cassettes, this is a considerable difference.
The reason for this development is first and foremost due to the increase in cassette speeds.
Now with 12-speed road groupsets, cassettes can have a wider range, and the differences between each gear can be relatively small.
For example, on the small part of the cassette, you may only have a difference of 1 tooth per gear, while the larger part will have a much larger difference. For example, if you switch to a 7-speed or 8-speed cassette, but keep the same gear range, the gears will be closer together.
Also, attitudes towards shifting have changed - "twisting" the chainring at a lower cadence is no longer seen as a sign of thigh pain, and our knees are much happier for it.
▲R9200 offers 12 speeds and a larger cassette than ever
Both Shimano and Campagnolo stuck with the existing gear ratios when moving to 12 speeds, using an extra sprocket as a means of compensating for the larger cassette, so the gears are closer together in use. SRAM went a different route (more on that later).
Shimano offers 11-28, 11-30 and 11-34 options in its latest R9200 groupset. These gear ratios also exist in Shimano's 11-speed configuration, but Dura-Ace R9100 does not have an 11-34 option.
Campagnolo offers an 11-29 option for all of its 12-speed kits, the largest cassette it can offer in its 11-speed ecosystem.
But now, the Italian brand is offering an 11-32 cassette option across the board. There is also an 11-34 cassette, but it is only available at the Chorus level and only supports Chorus rear derailleurs.
▲SRAM's road bike cassettes have gone in a different direction
Unlike the above two, SRAM has subverted the traditional gear ratio range as we understand it with its latest 12-speed AXS kit.
It adds a 12th sprocket to increase the gear ratio range of the cassette. At the same time, SRAM road cassettes start with a smaller 10t (this requires the use of an XDR freehub, which we will get to later).
SRAM has also improved its chainring sizes, which are smaller than the regular sizes, 50/37 (Red kit only), 48/35 and 46/33. In contrast, the more traditional chainring gear ratios are 53/39, 52/36 and 50/34.
SRAM cassettes are available in 10-28 (Force and Red only), 10-30, 10-33 and 10-36.
Mountain Bike Cassettes
▲Shimano offers two cassette options for its mountain bike kit
The size of mountain bike cassettes has also increased. This is mainly due to the emergence of 1x drivetrains. In 1x settings, there are no small chainrings for climbing, so the cassette needs to provide a larger gear change so that riders can match the gear ratio suitable for climbing.
Unlike road bikes, mountain bike cassette options are generally more limited.
Shimano only offers two cassette sizes in its 12-speed product line - 10-45 (not available at the Deore level) and 10-51. The 10-51 option can only be used on 1x settings, but the 10-45 can be used on 1x or 2x systems.
▲A few years ago, cassettes as large as the 10-50 in SRAM's Eagle groupset were uncommon
SRAM's Eagle series also only offers two cassette sizes - 10-50 and 10-52. The 10-52 is the cassette with the largest gear range produced by the two groupset manufacturers. Although there are currently two options, the 10-50 will most likely be phased out over time as it is replaced by the 10-52.
If you go with the 10-52 option, you will need to make sure you use a compatible rear derailleur, as the previous generation of Eagle mechanical rear derailleurs had a slightly shorter guide plate.
For users of SRAM's two entry-level Eagle groups, SX Eagle and NX Eagle, SRAM offers an 11-50 cassette. This allows the cassette to be mounted to a standard Shimano HG freehub (again, more on this later), as the 10t option requires the use of an XD freehub.
▲The new SRAM T-Type shifting kit only supports 10-52t cassettes
SRAM has since released its new shifting, completely eliminating the rear derailleur tail hook. The rear derailleur no longer has a limiter and set screw, so it only works with 10-52t cassettes.
Gravel cassettes
▲ All major shifting manufacturers have launched gravel-specific products
Gravel road bikes are best seen as a cross between road bikes and mountain bikes. Therefore, it is normal to see them equipped with road or mountain bike cassettes.
However, as kit manufacturers join the gravel riding craze, there are now gravel-specific cassette gear ratio options to choose from.
SRAM's XPLR AXS kit is designed specifically for gravel riding. The SRAM XPLR cassette has a range of 10-44 and requires a specially compatible rear derailleur. If you want a particularly wide-range 1x system, you can also mix and match the drop handlebar shifter with the mountain bike Eagle eTap AXS shifting kit. SRAM calls this a "mullet" setup.
You can also mix and match XPLR AXS shifters and cranksets with the new Transmission drivetrain.
▲SRAM's new Red XPLR AXS groupset differs from the rest in that it uses a derailleur mounted directly to the rear axle
SRAM's latest Red XPLR AXS groupset differs in that it relies on a derailleur mounted directly to the rear axle, similar to the Transmission mountain groupset. This differs from all other SRAM cassettes in that it is a 13-speed groupset and uses a 10-46t gear ratio.
▲Campagnolo's gravel groupset is 13-speed
Campagnolo is another manufacturer that makes a 13-speed groupset for gravel. The Campagnolo Ekar 13-speed gravel groupset offers a cassette with the smallest sprocket having only 9 teeth. The cassette is available in 9-36, 9-42 or 10-44 options. The Ekar is a 1x-specific groupset.
The next-level Campagnolo Ekar GT groupset is also 1x-only, but with the option of a 10-48t cassette.
Shimano GRX groupset owners can choose between 10-45 and 10-51t on the 12-speed 1x drivetrain, or 11-34 or 11-36t on its 2x combination.
For the initial 11-speed version, you can choose one of Shimano's own 11-speed road or mountain bike cassettes. Road cassettes can be up to 11-34, while mountain bike cassettes are available in 11-40, 11-42 or 11-46. Shimano's cassette range may sound more limited than its competitors, but it's also important to remember that GRX is a gravel groupset that is compatible with both 1x or 2x systems.
▲DT Swiss wheels using HG freehubs that support Shimano/SRAM cassettes
Freehub compatibility
The freehub has splines that engage with grooves on the cassette. These splines ensure that the cassette's sprockets are relatively unchanged in position and in the correct orientation for the entire shifting system to work properly.
Each shifting manufacturer has its own freehub design, which means that not all cassettes will work with every wheelset (or kit).
Shimano freehub
▲Shimano's HG freehub design has been the most common choice for many years
The most common system is the Shimano 11-speed HG freehub, which has 9 splines. Most Shimano kits used this style of freehub until the 11-speed era. SRAM kits before the current 12-speed SRAM kits also used the same freehub design, although there are a few exceptions, such as SRAM's 1x11 mountain kits.
When Ultegra and Dura-Ace moved to 12-speed, Shimano also released a new freehub design for its road kit, although 12-speed Shimano cassettes are also fully compatible with 11-speed freehubs.
On the mountain bike side, Shimano has matched its 12-speed Deore, SLX, XT and XTR kits with a new freehub standard called Microspline.
If you use a Shimano HG freehub, you need to consider how wide the cassette you buy is. Road freehubs are slightly wider than mountain freehubs (1.85mm wide), and 11-speed Shimano HG road cassettes are also slightly wider than 8-speed or 9-speed cassettes, also 1.85mm wide.
You can add 1.85mm spacers to the inside of an 11-speed road hub to fit a mountain or road cassette with fewer speeds, but you can't fit a road cassette on a mountain freehub. Since a 10-speed road cassette is narrower than an 8-speed or 9-speed cassette, you'll need to use a 1.85mm spacer plus a 1mm spacer to fit it.
Campagnolo freehubs
▲ The N3W freehub is a shortened version of Campagnolo's existing road freehub design
Campagnolo also has its own freehub spec that's different from Shimano and SRAM and not compatible with any of the competing products.
The brand has also introduced a new freehub standard called N3W to support its 13-speed Ekar cassettes. The adapter on this freehub also allows it to work with Campagnolo's older standard cassettes.
SRAM freehub
▲ SRAM's XD freehub body
SRAM introduced its XD freehub standard when it started to offer cassettes with a 10-tooth minimum cog. Recently, SRAM has transplanted this design to the road with the XDR, making it possible to have a 10t cassette on a road bike, but a little wider than the general road bike standard.
The SRAM XDR road freehub is 1.85mm wider than the SRAM XD MTB freehub. By using spacers, you can install an XD cassette on a road wheelset with an XDR freehub, but you can't use an XDR cassette on an XD freehub.
Mountain bike cassette vs road cassette
Some people may want to use a road cassette on a mountain bike, or vice versa. Here, we'll discuss why you might (or might not) choose to do so, and look at the compatibility issues that may arise from both options.
Most people won't want to use a road cassette on a mountain bike. Because traditional road cassettes have a much smaller gear range than mountain bikes, off-road riding requires a wider range of gears to get you up technical climbs while still having a small enough cassette to handle the descents.
▲ Unless you’re using a triple crankset, it’s unlikely you’ll want to use a road cassette on your mountain bike
If you’re still using a triple crankset, then a road cassette may have enough total gear range, but it’s a pretty “know-it-all” choice these days.
If you need an easier climbing setup, or you’re bikepacking, you might want to consider using a mountain bike cassette on your road bike. However, you’ll need to make sure your freehub and derailleur are compatible with a wider-ratio cassette.
The guide plate design of the rear derailleur is usually suitable for a certain range of gears. For example, Shimano’s Dura-Ace R9100-SS rear derailleur is designed to support up to 11-30 cassettes.
This means it is not compatible with 11-34 cassettes, because the guide plate of the rear derailleur is not long enough to give the derailleur enough tension when riding in the smallest tooth of the cassette. After all, the length of the chain needs to be long enough to be compatible with the larger 34t sprocket.
▲If you want to use an 11-34t cassette on a road bike, you need a long-legged rear derailleur
If you want to use an 11-34 cassette, in addition to buying the relevant model of cassette, you also need to buy a compatible rear derailleur. For example, Shimano's Ultegra R8050-GS or 105 R7000-GS rear derailleur. GS means these are "medium-leg" rear derailleurs. The same naming convention also applies to Shimano Di2 shifting.
SRAM AXS rear derailleurs are compatible with up to 33t road cassettes, and there is usually a "Max 33t" prompt written on the inside of the rear derailleur. There's also a 'Max 36t' option that pairs with a 10-36 cassette, and the XPLR derailleur can accommodate up to a 44t (or a 10-46t cassette with the Red XPLR AXS).
Campagnolo 12-speed derailleurs are compatible with up to 11-32. The only exception is the Campagnolo Chorus, which is compatible with up to 11-34.
If you're switching to a larger cassette, you'll also need to make sure your chain is long enough.
▲Shimano Dura-Ace R9200 has a carbon fiber "claw" to save weight
The cheapest cassettes are usually made of die-cast steel, which is hard-wearing but heavy. As the price increases, you tend to get higher-end materials and more refined finishes.
For example, five of the 12 sprockets on the top-level Shimano Dura-Ace R9200 cassette are made of titanium alloy. The smaller sprockets on the cassette still use steel because there are fewer bite points with the chain. Softer materials will wear faster.
▲Rotor and Miche also make cassettes compatible with mainstream kits, although the 13-speed Rotor 1x13 cassette in the picture is only suitable for Rotor's own kit
SRAM uses a one-piece CNC molding process for its highest-level SRAM Red AXS 12-speed road cassette, which can remove a lot of unnecessary material, thereby reducing weight. Rotor and Miche both save weight by using aluminum alloy to make cassettes compatible with mainstream road bike kits.
Larger sprockets are usually grouped together, supported by a single bracket (or "cage spider"), which snaps into the freehub.
This saves weight, and because it's not subject to wear from the chain, the bracket can often be made of lighter materials - Dura-Ace cassettes use carbon fiber for the cassette bracket
Some cassettes have individual sprockets, and the mid-range sprockets are usually separated by spacers, which may be made of alloy or sometimes plastic. Smaller sprockets come with their own spacers.
Most cassettes (but not SRAM XD and XDR) are fixed to the freehub body using a locking nut (cassette cover), which is part of the complete cassette. The default material is steel, but aluminum alloy is a lighter alternative available.
Cassette price: what do you get for your money?
▲SRAM's Red cassette is machined from a single piece of metal
You can spend a lot of money on a high-end cassette; the most expensive cassettes now cost more than £300. So what do you get for your money?
Higher-spec cassettes are often made from more unique materials, such as titanium or carbon fiber for some of the sprockets and their cages. Other cassettes, like the SRAM Red road cassette, are CNC-turned from a single piece. In general, higher-end cassettes are more refined and weigh less than cheaper cassettes.
Weight aside, there isn’t a huge performance difference between a Dura-Ace 11-28 cassette and the cassettes in a Shimano Ultegra or Shimano 105 groupset, so you can save a lot of money by stepping down.
SRAM has similar options, and with the advent of the Rival eTap AXS, SRAM has also introduced a more entry-level 12-speed cassette, providing a cheaper alternative to the Red and Force-level cassettes. The same can be said for SRAM mountain bike groupsets.
Keep in mind that the cassette is a wear part that needs to be replaced regularly.
If you usually replace your chain when the chain is stretched by 0.5 (11/12/13 speed) or 0.75 (10 speed and below) as measured by a chain ruler, then you can use a rule of thumb to estimate the life of your cassette, which is about three chains per cassette. Some people's cassettes may wear out better, while others may wear out faster. It all depends on how clean you keep your chain and your local riding conditions.
If you continue to use it in an excessively worn state, the cassette will also experience additional wear as the rollers on the chain stretch. Since the cost of replacing a high-end cassette is quite high, it is recommended that you pay more attention to maintenance to avoid unnecessary expenses.
