Ah yes the S Ram DD. I know almost nothing of these. But i am very intrigued. When i first heard of them i assumed they worked the other way around! A 7 Speed Hub and 3 Speed (front) derallieur. I figured that would be excellent because you would have many of the benefits of both systems. Range. Only the three chainrings would wear out but those are cheap to replace. Shifting at stand still. The fact that hub gears can be very durable. A rather good chainline Etc.

I must be missing something, why did they do it the other way around? Does what i suggest exist as a integrated gearing system? I guess you could always kinda put one together but...

Really like the S-Ram company. Innovative and good to see someone kinda messing with Shimano's hegemony.