>>2017557The way cassettes for hyperglide style freehub bodies normally work is that you have sprockets and spacers that fit onto a splined freehub body, and how many you can fit is limited by the length of the cassette body. It's possible to exceed that limitation by adding sprockets with a large enough interior diameter, on a carrier assembly that also has a sufficiently large diameter, that they overhang the base of the hub and spokes. This is why it's possible to make 12 and 13 speed MTB cassettes with massive sprockets that fit on existing 10sp freehub bodies. The same trick doesn't usually work for road cassettes because the sprockets just aren't big enough, though Shimano 12sp road cassettes do use this method to fit on 11sp bodies, and that's why 30t is the minimum largest sprocket size for them.
