I'm putting a 46x30 chainring with a pretty narrow tread on a frame. On the advice of my LBS I got a Sun XCD double FD, but I'm starting to think it's not right for this application. When I have the derailleur on the big ring and far enough out to avoid rubbing, there's razor-thin clearance between the outer plate and the crank arm. And that's just on the stand -- I'm worried that once I'm on it and things are flexing, the crank is going to hit the cage.
I think a narrow-cage derailleur, and maybe one that is designed for smaller chainrings (the Sun is listed at max 56T) will be a better fit. Does anyone have any recommendations?