Subcompact gearing - 42-28 possible with T47 BB?

[NHAero]

I have an update on this, because these compatibility things are really vexing (at least to me!) and I hope that this info helps the next person. I bought the North Shore Billet 104 spider, and figured out that the best gearing for my use was 40-28 instead of 42-28, and found that Shimano made an XT crankset with the 4 arm 104 BCD and a matched 40-28 chainring set. I got both in the mail today. The Shimano rings just barely don't fit on the NSB spider - they aren't symmetrical but rather have a slight angle to where they meet the "lands". So they don't fit. It looks as though it will be very little work with a file or dremel sanding drum to remedy this - the portion of the chainring that interferes is very thin. So it's going to work, but it's just an example of how non-standard things have gotten. I'm excited to be getting close to the solution (cranks come Friday, GXP BB early next week) and again very grateful to Mark McM for all the info making this possible.

Originally Posted by Mark McM

I've been looking into this quite a bit recently, so just to add a bit more:

Snip
Another feature feature of the North Shore Billet crank is that it uses a standard diameter for the chainring "lands", so that any 104mm chainrings will fit - SRAM spiders use a larger diameter for the chainring "lands", so only SRAM (or SRAM-specific aftermarket) chainrings will fit. .