In an effort to eliminate triple chain rings from mountain bikes while still delivering the wide-range gearing needed for mountain bikes, Shimano followed SRAM’s lead and introduced a new generation of wide-range 10 speed XT cassettes, aka, the Shimano CS-M771 10 speed XT Cassettes.
The one that most tandem teams have been oohing and aahing over is the 11-13-15-17-19-21-24-28-32-36 model that could allow them to use a compact double instead of the ubiquitous triple found on most tandems. Now, there have been similar cassettes offered by SRAM: the PG-1070, XG and XX as well as some IRD / Giang models. The latter have been problematic and while the PG-1070 is reasonably priced at $97, the XG ($300) and XX ($349) models have been cost prohibitive. The always reliable XT grade M771 carry’s an MSRP of $114 and I’ve seen them as low as $74 in the 34t and 36t models.
Me, I’m still anxiously awaiting the 11-12-14-16-18-20-22-25-28-32 model, as my original plan to switch over to Campy 10-speed 29t cassettes came to a screeching halt when I remembered that you need to do a bit more to your wheel than simply changing out the cassette freehub (anyone need a White Ind. Campy 10 speed freehub or Centaur 13x29t cassette?)