What is a bicycle cassette?
A bicycle cassette is the cluster of sprockets on your bike. The cassette is normally situated on the rear hub of your bike; slotting onto a freehub body, and held firmly in place with a threaded cassette lockring. Depending on the 'speed' of your bike, your cassette could have anything between a 5 and 12 sprockets; most modern bicycle drivetrains utilise either 9, 10 or 11 speed cassettes.
Why are cassettes important?
Cassettes provide you with a range of gearing options that your chain can run on. The range of gear ratios allows you to vary your pedalling cadence (revolutions per minute), to achieve optimum efficiency.
Running your chain on one of the larger sprockets (more teeth) on the cassette, will provide an "easier" gear; letting you turn your legs faster. Running your chain on a sprocket with a lower number of teeth, will allow you to keep pushing power through your drivetrain, without "spinning out" (pedalling at an uncomfortably high number of revolutions) on a downhill section or sprint. A good range of gears on your cassette, therefore allows you to select the optimal gear to use; to keep your pedalling as smooth and as fluid as possible.
How do you choose the right cassette for your bike?
The choice of a cassettes can appear overwhelming at first glance. There are different combinations of sprockets, to suit different tastes and terrains; with a significant difference between the cassette you would use for a triathlon bike, compared to a mountain bike cassette.
The main thing to consider is the spread of gears on the cassette. The closer the highest and lowest number of teeth is, the smaller the jump between gears; facilitating a smoother gear change. However, having closer geared sprockets will normally decrease the size of the largest sprocket on the cassette; leaving you with a gear ratio that may be less suited to climbing and tough terrain.
Mountain bike cassettes
Mountain bike cassettes have a larger range of sprocket sizes, due to the fluctuating gradients that characterize off-road trails. Riding a flat forest track and then hitting a steep technical climb, requires a major jump in gears. To accommodate this style of riding, the sprocket size jumps are larger; this is more important for mountain biking than providing the smooth shifting of small jumps between sprocket sizes that you get on road cassettes.
The creation of 10, 11, and now even 12 speed cassettes, was a significant develop for mountain biking. The larger number of sprockets on these cassettes, means that you can have an even larger biggest sprocket, without getting too great a jump between the teeth. This evolution allowed mountain bikers to do away with their triple chainsets, which provided a small get-out-of-jail chainring, and instead run double or even single chainsets; reducing weight, clutter and potential mechanical problems, as a result.
10 speed mountain bike cassettes now come in sprocket ranges such as 11-32, 11-34 and 11-36. Wiggle's best selling 10 speed mountain bike cassette is the Shimano Dyna-Sys Deore XT 10 Speed Cassette
11 speed mountain bike cassettes come in even larger sprocket ranges, providing even greater gear ratio choice, such as 11-40 and even 10-42! Wiggle's best-selling 11 speed mountain bike cassette is the Shimano Deore XT M8000 Cassette (11-42)
Road bikes cassettes
Road bike cassettes have a smaller largest sprocket than most mountain bike cassettes, with a resultant smaller jump between the teeth sizes. Most road bike cassettes will have an 11, 12 or 13 tooth smallest sprocket; then between 21 and 32 teeth on the largest sprocket.
The vast majority of road bikes come fitted with a 12-25 cassette, and when paired with a compact or standard chainset, this is suitable for most cycling terrain - except for very mountainous riding.
If you ride lots of hills, or you struggle with hill climbing, a cassette with a lower ratio largest sprocket (a greater number of teeth i.e. 27+) may be beneficial; it will allow you to keep spinning for longer, rather than grinding.
When selecting your cassette for your road bike, ensure that your derailleur will accommodate the largest sprocket size on the cassette. A longer cage rear derailleur is required to accommodate larger sprockets; as it accommodates the greater length of chain required to go around the larger number of teeth. Use a small cage derailleur with a large sprocket cassette, and you'll risk over stretching the derailleur, and you'll encounter a lot of slack chain when riding in the smaller sprockets on the cassette.
Compatibility between different cassettes
Sometimes, you can run a different brand cassette to the brand of the rest of your drivetrain; such as a SRAM cassette with a Shimano derailleur.
However, this is not always the case. You should note the following cross-compatibility of cassette options:
- SRAM and Shimano cassettes, on either road or mountain bike, are interchangeable with each other; as the spacing is the same between the sprockets.
- Campagnolo road cassettes will only work with Campagnolo drivetrains.
A freewheel threads directly onto the hub shell, rather than onto a freehub body. The ratchet system is built into the freewheel mechanism. Freewheels are becoming less and less common on bikes, and now they are usually only found on entry level products/bikes with 6/7/8 speed groupsets. The choice is not vast and only a few brands product freewheels, such as the Shimano MF TZ21 7 Speed Freewheel.