My wife's 1980s Trek touring bike. I originally set it up with 9-speed Shimano barcons and a 3 x 9 touring configuration. Because she claimed that gearing was confusing to her, I chose to use a rapid rise (XT, I think) MTB derailleur so that when she pulled back on a shifter, the gearing got higher - same for both sides.
Now three years later, she'd like STIs with little gear indicators windows. No problem finding 3 x 9 Tiagra or somesuch, but I'm concerned about the rapid rise rear derailleur.
I've searched several older threads on this, and they discuss the limitations on downshifting (one click at a time with the small paddle), but no one had suggested that it wouldn't work. So, is it worth trying out with the existing derailleur? The return spring has plenty of oomph for barcon control, so why not STI?
My wife isn't a multiple cog in one shift type of person anyhow. She maintains a fairly high cadence and makes frequent shifts, so double clicking on the small lever for downshifts won't be an annoyance to her (I think).
I'd rather not swap out the derailleur if I don't need to...