Originally Posted by
HillRider
Shimano still offers the 12x27 10-speed in 105, just not in Ultegra or Dura Ace anymore. I agree that a 12x28 or, better yet, a 13x27 or 13x28 should be available. DIY Shimano custom cassettes are very limited by the availability of suitable single cogs and the grouping of multiple cogs on spiders.
I have built a custom 13x27 9-speed by obtaining a 13T first position cog and a single 16T cog but locating the 16 was very difficult and I don't think they are available in either 8 or 9-speed form from anywhere these days.
Campy sells 13x29 10-speed cassettes which include the 16T and 13x26 10-speed which have both the 16T and 18T. The also have 11-speed 12x27 cassettes which have both the 16T and the 18T cogs.
If the OP wants 12-27 he might as well get 105, it's only 16g heavier (when you compare the equivalent 11-23 cassettes 219g vs 203g) and will be nice and durable. Having said that, they didn't mention anything other than wanting an 11-28.