This article is your guide to work on Shimano and Shimano-compatible 7-speed cassettes (sprocket clusters) -- how to find replacements for worn sprockets, make substitutions, and build custom combinations. Tables, below, list available combinations.

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.

7-speed cassettes are still found on many older bicycles. Replacing a worn 7-speed cassette with a new one avoids the need to replace anything else, except the chain. As of 2010, many bicycles are still being sold with 7-speed freewheels.When you need to replace a wheel, you may upgrade to one with a 7-speed cassette Freehub and avoid having to change the shifters. You may have to look for a used or ne old stock 7-speed cassette hub, though.

Seven sprockets enough? More sprockets must be better, right? Not necessarily! The trend toward more sprockets is driven largely by spec hype. Two chainwheels and 7 sprockets can provide everything most cyclists need. Still not enough? A third chainwheel adds much more than an 8th, 9th or 10th sprocket.

7 and 8-speed systems use a relatively wide, and almost identical, spacing between sprockets, and the same tried-and-true chain. 8 or more speeds require a longer rear axle. Rear-wheels get weaker as dishing becomes more extreme. Cornering clearance is reduced and tread width ("Q factor") increases. With 9-speed systems -- even more, 10-speed -- index shifting becomes finicky as sprockets crowd closer together. Each new generation of chain is narrower, weaker and harder to service.

Certainly, most bicycles with 7-speed cassettes can be upgraded to 8, 9 or 10 speeds. There's information on this site on how to do that. But, you also can stay with 7 and you don't have to regret it. Some kinds of 7-indexing speed shifters are getting hard to find, but 8-speed shifters will work with a 7-speed cassette and a bit of alternate cable routing.

Cassettes listed in the table below will fit most Shimano and Shimano-compatible freehub bodies, with the following exceptions:

• Aluminum 10-speed bodies with taller splines work only with 10-speed sprockets
• The wider 8/9/10-speed freehub body requires a 4.5 mm spacer behind a 7-speed cassette. You might as well stay with the larger number of sprockets if the hub already has this freehub body.
• 11-tooth sprockets require a "Hyperdrive C" freehub and lockring (made in both 7-speed and 8-speed versions).
• The Capreo 9-speed body has four special sprockets, with 9, 10, 11 and 13 teeth, in 9-speed spacing, so there's no way to use it with 7-speed or 8-speed sprocket spacing.

The ramps and shaped teeth of Shimano Hyperglide cassettes and similar cassettes from other manufacturers, listed in the tables below, improve shifting in the intended sprocket progressions. It is possible to mix and match sprockets with some small penalty in smoothness of shifting. You may also use older Uniglide sprockets, though these are becoming rare.

Model numbers covered in current (2010) Shimano product literature are in boldface in the tables, like this: CS‑HG30‑I. 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.

Shimano identifies many sprocket combinations by one-letter or two-letter codes such as "M" or "ac". Cassettes with the same code always have the same tooth counts, though they may use different bolted combinations of sprockets.

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

SRAM, IRD and SunRace offer 7- and 8-speed Shimano-compatible cassettes -- listed below the Shimano section.

Of all the cassettes listed below, the one I [John Allen] like best is the Shimano M cassette. It has an even progression of ratios, without a big jump in the middle like many other Shimano cassettes (including 8- and 9-speeds!). With triple chainrings, the M cassette provides a very nice selection of drive ratios.

Miche sprockets are available individually in all sizes, useful in building up a custom progression. Taking all of these options into account, there is plenty of variety available to keep a 7-speed system going.

Click here for 7-speed cassettes available from Harris Cyclery

Also see Shimano technical documents:

CS-HG30-I 7-speed, ac group
CS-HG50 at group
CS-HG50 installation instructions

The CS-HG30-I is an Interactive Glide cassette with wider sprockets and narrower spacers, and must be used with Interactive Glide chain.

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.

For example, Shimano doesn't make any true "corncob" (one-tooth-jump) cassettes for time-trialists or flatland riders. In 7 speed, the closest is the J (13/14/15/16/17/19/21).

If you remove the 21-tooth sprocket from a J, you can make it into a 13-19 corncob by buying an 18 to put between the 17 and the 19. Alternately, you could make it into a 12-18 by removing the 19 and the 21, and buying a 12 and an 18.

Similar modifications can be done with other ratios. 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.

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 8-speed sprockets into 7- speed cassette. 9- or 10- speed sprockets, especially in the smaller sizes (11, 12, 13) that feature built-in spacers, may not allow enough clearance between sprockets, and the chain may rub on the next sprocket.

There are tricks that make it possible to install 8, 9 and maybe even 10 sprockets on a 7-speed cassette body. There's information on this site on how to do that.

Harris Cyclery sells some custom cassettes, with sprocket combinations you may find useful (though no 7-speeds):

Sprockets are available individually, too:

Shimano listed 11 old-style "Uniglide" cassettes in its 1997 catalog. These are mostly oddball combinations, (too rare to be worth tooling up for a Hyperglide version). They are listed here for reference. -- you will not find them for sale at your Local Bike Shop, but you might find one at a flea market. The 22-tooth sprocket can be especially useful, because 22-tooth Hyperglide sprockets are rare. (Miche does make a sprocket in this size, though).