Please bear with me as I figure out how I'm going to format these. Figuring out what constitutes "enough, but not too much" information can be difficult - especially something like this that is related to so many other topics.
Below are the individual tooth counts for 10-speed cassettes. The first column in each box is individual cog sizes, second: the inverse of the cog number in the second column (obviously expressed as a percentage - this represents the minimum difference between the cog and another larger cog), and the difference between the cog and the next smaller, also expressed as a percentage.
Sram and Shimano cassettes are interchangeable - they use the same cog-cog spacing (meaning a Shimano shifter-derailleur combo will shift a Sram cassette, provided they are all 10-speed, and vice-verse), Campagnolo have a different spline, and thus require a specific hub (and to my knowledge, there are no disc, 135mm or thru-axle, Campagnolo-freehub hubs on the market) and slightly different cassette spacing. There are ways of re-spacing Shimano cassettes to Campy spacing, as well as Shimano-splined, Campy spaced cassettes out there, but I'm not going into that yet (mostly because I feel those options are fairly pointless now, as good quality setups are available with either spline and spacing).
I think it's worth pointing out that on some "sizes" i.e., 11-36 (smallest and largest cog) between Shimano and Sram, there are a number of different intermediate cogs. Generally, the goal of the cassette designer in selecting cog sizes is to have an even percentage jump on every cog (the last column), but since cogs have to have an integer number of teeth, this isn't possible (the gap can only be a multiple of the second column).
Another interesting note is how the line between what is "road" and "mountain gearing has sort of disappeared. With 9-speed the smallest mountain cassette had a 32t large cog, where the largest road had 26 or 27 depending on the brand with nothing in between available. Now Shimano offers 36, 34, 32, 30, 28, 27, 26...
I believe all Sram and Campy cassettes available are included in the list. Shimano offers a number of "Junior" gearing options (the UCI has maximum gearing rules for junior racers; so standard gearing isn't allowed in Junior races): 13-25, 14-25, 15-25, 16-27 that they don't publish individual cog lists for (while I'm pretty sure I could guess correctly, I'm trying to avoid writing anything I don't know to be correct).
Sram recently rolled out an 11-Speed mountain setup - interestingly enough they are the only company that doesn't yet have an 11-speed road offering, and the only one that has 11 mountain. Currently they only offer one cassette option, 10-42, the system is single chainring-specific, this article explains why. The 10-tooth cog required a special freehub, as the standard shimano-splined freehub is larger diameter than a 10-tooth cog would be.
The above linked article also talks briefly about the limit of how small cogs can get: the polygon effect. A chain wrapped around a cog is not actually round, it forms a polygon - the chain pins being the corners, the links being the sides. Obviously the bigger the cog, the more sides it has, the closer it approximates a circle.
Above is a list of the same information as the first chart, but for 11-speeds. Shimano just introduced Dura-Ace 11-speed, and I wasn't able to find individual tooth-counts for their cassettes - the overall size are listed. Sram XX1 uses it's own freehub design, Shimano requires an 11-speed specific hub, Campy 9, 10, and 11-speed freehubs and cassettes are all compatible. All these systems require dedicated chains, derailleurs and shifters.
The XX1 drivetrain uses specific chainrings (See the heading "No chain guide required?")
...alternating tooth thicknesses that are synchronized with the gaps in the
chain – slightly narrower to fit in between inner chain plates and
wider to take advantage of the extra space between outer chain plates.
In order to keep the chain in phase with the alternating rings, only rings and cogs with even numbers of teeth are allowed, furthering the size-increment issue.
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