Indexed rear-shifting systems from Shimano, SRAM, Campagnolo and SunTour have different amounts of

• cable travel per click,
• derailer movement for a given amount of cable travel, and
• sprocket-to-sprocket spacing.

(Almost any cassette which fits a Shimano cassette body, though, will have the Shimano spacing).

It's often useful to mix and match components to keep an old wheel in service, if you like a particular kind of shifter, etc. etc.

Some nonstandard combinations work with components right out of the box. To achieve a working combination, you also could change the derailer, shifter -- or sprocket spacing:

• There are two common thread-on freewheel sprocket spacings. Most 7-speed freewheels are compatible with Shimano 7-speed spacing, and most 6-speed freewheels, with Shimano 6-speed spacing. For details, see the sprocket spacing cribsheet on this site.
• Almost all Shimano cassettes with 8 or more sprockets fit the same hubs: inter-sprocket spacing decreases with the number of sprockets. The shorter sprocket space of a hub made for a 7-speed cassette will accept 8 sprockets of a 9-speed cassette, or 9 sprockets of a 10-speed cassette. Instructions are here. You usually can also replace a hub's shorter 6- or 7-speed cassette body with an 8-9-10 speed body. Instructions are here.
• There is some compatibility among Campagnolo cassettes with different numbers of sprockets.
• IRD sells cassettes to fit Shimano hubs, but with Campagnolo inter-sprocket spacing.

Other options are to use cable-travel adaptor pulley -- or re-route the cable at the rear derailer to increase or decrease its motion.

These adaptations are described next, followed by links to tables listing combinations that work.

Jtek Shiftmate adapter installed on Shimano derailer

Cable-travel adapters use a double, side-by-side pulley with grooves at two different diameters. The cable enters at one diameter, and exits at the other. An adapter can be installed either to increase or to decrease cable travel.

Harris Cyclery does not sell JTek Engineering's Shiftmate cable-travel adapters, due to the several different kinds and low demand -- order these direct.

Correct ratio does not guarantee success. There also are placement issues; and an adapter may run out of cable travel. JTek does not recommend use of Shiftmate adapters with some derailers, including Shimano XTR derailers. Ask, before you buy.

Most of the JTek Shiftmate adapters are available either angled, for use at the rear derailer, or straight, for use in mid-cable or at a cable stop.

Harris Cyclery can supply the Problem Solvers Travel Agent. The Travel Agent is intended mostly to make direct-pull brakes work with ordinary brake levers, but it also works with derailers. It is not intended to solve derailer cable-travel issues.

Most pulleys used on bicycle cables, including those in shifters, are small enough that the cable will eventually develop metal fatigue (like a paper clip being bent back and forth), fray, and part. This problem is generally tolerated in shifter cables -- but carry a spare cable. A pulley-type adapter adds one more place where this can happen.

Two alternate cable routings for Shimano derailers adapt them for use with nonstandard shifters or cassettes.

Shimano has publicized an alternate cable routing which places the cable slightly closer to the pivot, making the derailer move slightly farther for each click. This adaptation makes newer Shimano derailers work with older Dura-Ace shifters, but it is also useful (though nonstandard and not as accurate) when you want to use a 9-speed cassette with 10 speed shifters, or 8-speed cassette with 9-speed shifters, or a 7-speed cluster with 8-speed shifters.

The other alternate cable routing, suggested by Brian Jenks, proprietor of Hubbub Cycles, decreases the derailer travel for each click. This makes some Shimano derailers and shifters compatible with Campagnolo cassettes. It is also useful when you want to use a 10-speed cassette with 9-speed shifters, or 9-speed cassette with 8-speed shifters, or an 8-speed cluster with 7-speed shifters. You will lose the use of one sprocket, unless you are using a shortened cassette such as a Shimano Linksys cassette, an 8 of 9 on 7, or 9 of 10 on 7. Note the two tabbed washers in the drawing below -- one to change the cable routing, and the other (with its tab facing to the right in the picture) to secure the cable.

Unlike the JTek shiftmate adapters and the Dura-Ace modification, the other altenrate cable routings are not standardized. To get the indexing to match the sprocket spacing, you will have to check and readjust the place where the cable attaches.

This article links to tables showing combinations of shifter, rear derailer, sprocket spacing and adapter (if used) which achieve correct indexing. Here's how to use the tables.

1. Look up the sprocket spacing of the cassette or freewheel you intend to use, in the sprocket-spacing cribsheet. Measure the sprocket spacing, if you are in any doubt.
2. Go to the compatibility table page and select the tab for the sprocket spacing of your cassette or freewheel (any of several values from 3.85 through 5.5 mm). Across the top in each tabbed section is a list of derailer types, and down the left side, a list of shifters. Highlighted combinations work with your cassette or freewheel. Some combinations require an adapter, as indicated by the color code in the cell. The number of available speeds is that of sprockets or shifter clicks, whichever is smaller. You won't necessarily have an orphaned sprocket with, say, an 8-speed shifter and 9-speed spacing. You may, for example, be using a Shimano Linksys 8-speed cassette, which uses 9-speed spacing, or you may have an 8 of 9 on 7 or 9 of 10 on 7 installation.
3. Follow the color code in the table cell to identify the adapter needed, if any. Note that the same adapter can be reversed to increase or decrease cable travel.
4. Note also that cable pull also differs for front derailers. With double chainwheels, most shifters and derailers will work. With triple chainwheels, and especially with indexed front shifters, there can be incompatibility due to the need for trimming. Also, cable travel differs between Shimano's "road" and "mountain" front derailers. See details here.

The settings in the tables in boldface with no adapters are as intended by the manufacturers. How close to these does indexing have to be? Try and see. In a few cases, I have allowed loose tolerances where no other available combination would even be close. You could try combinations with loose tolerances if you like. The tables list all possible combinations.

Combinations with longer cable pull at the shifter are likely to work best. Combinations with no adapter or a decrease-ratio adapter are likely to work better than ones with an increase-ratio adapter. Combinations using Shimano derailers with the "Hubbub" cable routing are likely to be less accurate than others.

Sheldon Brown, founder of this Web site, compiled the table of sprocket spacings on which much of the work here is based. He also described some nonstandard combinations. Chris Juden, of the Cyclist Touring Club (U.K.), explored nonstandard combinations systematically, and has published information about them. JTek Engineering and Quality Bicycle Products have been very helpful in providing technical data on their products.

I have built on all this work, developing a step-by-step approach, and covering many additional freewheels, cassettes, shifters and derailers. I think that the information is mostly correct, though its development has been mostly a math exercise based on manufacturers' specs, collected data and a few measurements. Results are not guaranteed, but I will take responsibility for correction of any errors. Please write in to let me know of what succeeds and what doesn't.