Dead Rats wrote:
watch out for chainstay clearance with something as big as a 39 in the middle
Don't think that'll be an issue as the double set up uses the outer two positions & not the granny ring mounting position.
It has a 47.5mm chainline to being the two rings a little closer in to the BB to give a better spread of usable gears
It's a 4 bolt system, smallest ring is a 26t in the inner position, which is as FC points out a lower ratio then quite a few retro set ups
Might go up to a 40t outer, but seen as with my 1x9 set up a 32t chainring was enough to keep me going up to 30mph on the road I reckon anything bigger will be a waste on me, I hardly ever use the 'big' ring on triple set ups (44 or 42t)
I reckon a double it is, a 26t small ring & a 39t outer ring