I am changing my Ultegra 9-speed cassette combination to find out what suits me best. The inner five cogs are held together by 3 rivets. According to Barnett, these rivets are put in by the mfgr to make installation simpler and can be removed if desired. So, that's what I did.

Looking at each cog, they all have the designation xxt, as in 13t, 14t, etc. But they ALSO have other letters such as C1, C2, etc. Barnett says that even cassettes from the same mfgr may NOT be compatible (so putting an 18t between a 17t and 19t may not fit according to Barnett). He recommends using the table from the mfgr which lists compatibility.

I went to Shimano's website and dowloaded the cassette service and exploded view files. However, I cannot find any table that lists what cogs are compatible with each other.

Does anybody know where I can get that info on-line, or do I need to call Shimano and get pushed from person to person to person to person...?

http://www.sheldonbrown.com/k7.html

He has everything you every would want to know about cassettes.

Thanks. I had gone there and read that article. However, he doesn't discuss the letters stamped on the cogs. It SEEMS that all ultegra 13-16t cogs (which are colored black on the chart) are interchangeable, and all 17t+ cogs are interchangeable (and colored green on the chart).

Would that be a fair statement (so long as the jump isn't more than 3 teeth)?

I am changing my Ultegra 9-speed cassette combination to find out what suits me best. The inner five cogs are held together by 3 rivets. According to Barnett, these rivets are put in by the mfgr to make installation simpler and can be removed if desired. So, that's what I did.

Looking at each cog, they all have the designation xxt, as in 13t, 14t, etc. But they ALSO have other letters such as C1, C2, etc. Barnett says that even cassettes from the same mfgr may NOT be compatible (so putting an 18t between a 17t and 19t may not fit according to Barnett). He recommends using the table from the mfgr which lists compatibility.

I went to Shimano's website and dowloaded the cassette service and exploded view files. However, I cannot find any table that lists what cogs are compatible with each other.

Does anybody know where I can get that info on-line, or do I need to call Shimano and get pushed from person to person to person to person...?

I believe that the cog compatability has to do with the ramps being the the correct position relative to the next cog. For instance, if you put together a 17,18,19 by using the slipping a 18 between the the 17 and 19 of a 12-23; the ramps will not line up. - TF

If you look at the tips of the cog teeth from front to back, you'll notice that they are not lined up one behind the next. Instead, the tips form a spiral pattern. The cogs are "timed" radially with respect to the ones on each side.

If you create a gearing progression that the manufacturer does not make as a standard, the cogs will NOT be properly timed. The shifting may still be OK, but not as good as intended.

If you want a different combination and want it properly timed, it has to come from the manufacturer.

It's rare that a manufacturer does not offer all of the most sensible combinations. Shimano offers all the sensible combinations up to a 12-27. Campy does not offer a 12-27 and until recently did not offer a 12-23 10 speed (which has an 18T cog). Apparently campy feels that the 21-24 and 24-27 jumps are too large, but the larger jumps are often not objectionable on steeper roads.