This article is your guide to work on Shimano and Shimano-compatible 8-speed cassettes (sprocket clusters) -- how to find replacements for worn sprockets, make substitutions, and build custom combinations. The tables below list current models from major brands, and some discontinued models.

If you're not sure whether your bike has a cassette Freehub or a thread-on freewheel, we have a separate illustrated article explaining how to tell them apart.

Another article on this site gives more general information about cassettes.

More sprockets must be better, right? Not necessarily! The trend toward more sprockets is driven largely by spec hype. A second or third chainwheel adds much more than one more sprocket.

7- and 8-speed systems use a relatively wide, and almost identical, spacing between sprockets. With 9-speed systems -- and even more so, 10-speed systems -- index shifting becomes more finicky as sprockets crowd closer together. The newer, narrower chains are weaker and harder to service.

Though shifters are different for 8, 9 and 10-speed cassettes, the same rear derailers index properly with 7- through 10-speed Shimano cassettes. Most Shimano-compatible freewheel bodies accept 8-speed cassettes.. Note the following exceptions:

• Aluminum 10-speed freehub bodies with taller splines work only with 10-speed sprockets
• The wider 8-speed cassette does not fit on the narrower 7-speed body. To get more than 7 sprockets on thsi body, you would need to modify the largest sprocket of an 8-speed cassette or install only 8 sprockets from a 9-speed cassette or 9 sprockets from a 10-speed cassette. A simpler alternative is to replace the 7-speed cassette body with an 8/9/10-speed body.
• An 11-tooth sprocket requires a "Hyperdrive C" freehub and lockring
• Shimano "Nexave" cassettes and a couple of IRD cassettes have 8 sprockets, in the narrower 9-speed spacing. A spoke-protector disk takes the place of the innermost sprocket. These cassettes are listed with the 9-speed cassettes.
• The Capreo 9-speed body has four special sprockets, with 9, 10, 11 and 13 teeth, so there's no way to use it with 8-speed sprocket spacing.
• Pre-1997 Dura-Ace derailers work only with Dura-Ace shifters of that era; "Shadow" series MTB derailers work only with 10-speed "Shadow" shifters.

Many Shimano sprocket combinations are identified by one-letter or two-letter codes such as "W" or "ab".

In the Shimano table, model numbers covered in 2010 Shimano product literature are in boldface, like this: CS‑HG30‑8I. Older model numbers are included to help you choose replacements.

Some Shimano flat steel sprockets and spacers are in bolted or riveted assemblies, indicated by tooth counts in italics in the table below. The bolts or rivets only serve to keep sprockets and spacers in order when the cassette is not installed on the freehub. They can be removed to replace sprockets or build up custom combinations..

The Shimano parts lists linked below will help you identify models and order replacement parts.

Shimano-compatible 8-speed cassettes are available from SRAM, IRD and SunRace -- see additional sections below the Shimano section. Miche sprockets are available individually in all sizes, also useful in building up a custom progression. Taking all of these options into account, there is plenty of variety available to keep an 8-speed system going. However, shifting will not be as smooth with custom combinations as with stock cassettes.

Click here for current stock at Harris Cyclery

CS-HG60-8I, CS-8G50-8I 8-speed, an group CS-HG50-8I 8-speed, aw group CS-8G50-8, S/T/U/V/W group

CS-HG40 8-speed, an/aw group CS-HG40-8i 8-speed, ao group (Megarange) CS-HG30-8i 8-speed, an/aw group

Model numbers ending in "I" have Interactive Glide thicker sprockets and thinner spacers, and should only be used with Interactive Glide chain.

When these cassettes skip the same sprocket sizes, it is fair to assume that the sprockets are interchangeable while maintaining smooth shifting.

SunRace also makes 8-speed cassettes with 9-speed spacing and a spoke protector in place of the innermost sprocket, like Shimano Nexave.

SunRace 2010-2011 catalog

Shimano wants you to use one of its standard combinations, and offers a wide-enough choice to suit the needs of most cyclists, but you don't have to if you don't want to! It is not difficult to customize Shimano cassettes. If you substitute an un-approved cog, Uniglide or Hyperglide, SRAM, IRD, Miche, or some other brand, it will still work, but the shift to/from that cog will probably not be as smooth as a Hyperglide shift normally is. Since people managed without Hyperglide for several decades, this shouldn't scare you off. In particular, if you substitute the top or bottom sprocket, you will only have one shift that isn't HG; shifts to or from the extreme sprockets tend to be less troublesome than intermediate shifts anyway.

Generally, the smallest sprocket needs to be one with a built-in spacer, designed for the top-gear position. While you can't insert or remove a sprocket within a spider module, you can add sprockets on either side of these modules.

For example, if you want a 13-34 8-speed, you can start with an 11-28 -- the stock HG-50 11-13-15-17-19-21-24-28 has a sweet sequence of gears just as it is -- but to use a larger chainwheel or get a lower bottom gear, you might make this modification:

• Replace the 11 and 13 with a top-position 13.
• Add a spacer and a 34 after the 28. (You don't need to buy the spacer, because you can use the spacer that came between the original flat 13 and the 15.)

Shimano cassettes that don't use spiders have most of the sprockets held together by 3 small bolts or rivets. These are not essential. Their function is convenience, in allowing the cassette to be installed slightly more easily. To make a custom cassette, you will often need to remove the screws or rivets. Just discard them, they are unnecessary in practice.

• Some cassettes use screws with a 4 mm hex head. These can be removed with an adjustable wrench.
• Some cassettes use screws with a 2 mm Allen head. These are frequently mistaken for rivets.
• The easiest way to remove rivets is to grind off the heads where they protrude from the largest sprocket. I generally do this on a bench grinder.

There is no problem mixing, say, thinner 9-speed speed sprockets into an 8-speed cassette. You might use a thicker, 7-speed spacer to compensate for a thinner, 9-speed sprocket (see spacing cribsheet). The smaller sprocket sizes (11, 12, 13) that have built-in spacers should ideally be matched, but even this isn't generally a problem in practice.

Taking apart stock cassettes is a convenient way to find sprockets to build up your own combination. Miche sells individual sprockets, though they may not be easy to order. The catalog linked below is in Italian...